Macquarie University ResearchOnline...Fluorescence microscopy has become an essential tool to study biological molecules, pathways and events in living cells, tissues and animals

Macquarie University ResearchOnline

This is the published version of: Yujia Liu ; Hao Xie ; Eric Alonas ; Philip J. Santangelo ; Dayong Jin ; Peng Xi,

2012 ‘CW STED nanoscopy with a Ti:Sapphire oscillator’ in Optics in Health

Care and Biomedical Optics V : 5-7 November 2012, Beijing, China, edited

by Qingming Luo, Ying Gu, Xingde D. Li, Proceedings of SPIE, Vol. 8553

(SPIE, Bellingham, WA, 2012), article CID no. 85531B

Access to the published version: http://dx.doi.org/10.1117/12.2000807 Copyright: Copyright 2012 Society of Photo Optical Instrumentation Engineers. One print

or electronic copy may be made for personal use only. Systematic

reproduction and distribution, duplication of any material in this paper for a fee

or for commercial purposes, or modification of the content of the paper are

prohibited.

http://dx.doi.org/10.1117/12.2000807

CW STED Nanoscopy with a Ti:Sapphire Oscillator

Yujia Liua,b, Hao Xieb, Eric Alonasc, Philip J. Santangeloc, Dayong Jind, Peng Xib*

aSchool of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China; bDepartment of Biomedical Engineering, College of Engineering, Peking University, Beijing, China; cWallace H

Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, United States of America; dAdvanced Cytometry Labs, MQphotonics

Research Centre, Macquarie University, Sydney, New South Wales, Australia

ABSTRACT

Fluorescence microscopy has become an essential tool to study biological molecules, pathways and events in living cells, tissues and animals. Meanwhile, the conventional optical microscopy is limited by the wavelength of the light. Even the most advanced confocal microscopy or multiphoton microscopy can only yield optical resolution approaching the diffraction limit of ~200 nm. This is still larger than many subcellular structures, which are too small to be resolved in detail. These limitations have driven the development of super-resolution optical imaging methodologies over the past decade.

The stimulated emission depletion (STED) microscopy was the first and most direct approach to overcoming the diffraction limit for far-field nanoscopy. Typically, the excitation focus is overlapped by an intense doughnut-shaped spot to instantly de-excite markers from their fluorescent state to the ground state by stimulated emission. This effectively eliminates the periphery of the Point Spread Function (PSF), resulting in a narrower focal region, or super-resolution. Scanning a sharpened spot through the specimen renders images with sub-diffraction resolution. Multi-color STED imaging can present important structural and functional information for protein-protein interaction.

In this work, we presented a dual color, synchronization-free STED stimulated emission depletion (STED) microscopy with a Ti:Sapphire oscillator. The excitation wavelengths were 532nm and 635nm, respectively. With pump power of 4.6 W and sample irradiance of 310 mW, we achieved super-resolution as high as 71 nm. We also imaged 200 nm nanospheres as well as all three cytoskeletal elements (microtubules, intermediate filaments, and actin filaments), clearly demonstrating the super-resolution resolving power over conventional diffraction limited imaging. It also allowed us to discover that, Dylight 650, exhibits improved performance over ATTO647N, a fluorophore frequently used in STED. Furthermore, we applied synchronization-free STED to image fluorescently-labeled intracellular viral RNA granules, which otherwise cannot be differentiated by confocal microscopy. Thanks to the widely available Ti:Sapphire oscillators in multiphoton imaging system, this work suggests easier access to setup super-resolution microscope via the synchronization-free STED A series of biological specimens were imaged with our dual-color STED.

Keywords: Stimulated emission, super-resolution, point spread function, diffraction limit

1. INTRODUCTION Fluorescent microscopy has become an essential tool to study biological molecules, pathways and events in living cells, tissues and animals. Meanwhile even the most advanced confocal microscopy can only yield optical resolution approaching Abbe diffraction limit of ~200 nm. This is still larger than many subcellular structures, which are too small to be resolved in detail. These limitations have driven the development of super-resolution optical imaging methodologies over the past decade [1].

Multiphoton microscopy had been placed hope on reaching super-resolution with its nonlinear excitation. It has been widely applied in both biological microscopy as well as in clinical imaging-based diagnosis, due to its pinhole-less detection, deeper penetration depth, and dramatically reduced photobleaching. The resolution of MPM is still in the regime of micron level, as the wavelength is generally doubled comparing with that of single-photon microscopy

*[email protected]; phone +86 10 6276 7155; fax +86 10 6276 7155; http://bme.pku.edu.cn/~xipeng/

Optics in Health Care and Biomedical Optics V, edited by Qingming Luo, Ying Gu, Xingde D. Li, Proc. of SPIE Vol. 8553, 85531B · © 2012 SPIE · CCC code: 1605-742/12/$18

doi: 10.1117/12.2000807

Proc. of SPIE Vol. 8553 85531B-1

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/18/2013 Terms of Use: http://spiedl.org/terms

counterparts. On the other hand, several novel techniques on breaking the resolution barrier of diffraction limit have been reported in last decade, such as STED [2], SSIM [3], and PALM[4] /STORM [5]. Stimulated Emission Depletion (STED) is the first and optically straightforward method to effectively unlock the diffraction limit for far-field nanoscopy. Although STED is very promising and has attracted many interests in biological super-resolution imaging, the budget of affording such a system, especially the laser, is still a great barrier to its wide instrumentation and application just like MPM [6].

In stimulated emission depletion (STED) microscopy, the excitation focus is overlapped by an intense doughnut-shaped spot to instantly de-excite markers from their fluorescent state to the ground state by stimulated emission. This effectively eliminates the periphery of the Point Spread Function (PSF), resulting in a narrower focal region, or super-resolution. Scanning a sharpened spot through the specimen renders images with sub-diffraction resolution. In this paper we describe the realization of STED nanoscopy with Ti:Sapphire oscillator, a laser system typically used in MPM.

2. THEORETICAL ANALYSIS 2.1 Point spread function

The resolution of conventional microscopy is constrained by the Abbe diffraction limit:

2d

NAλ=

(1)

In confocal laser scanning microscopy, the PSF of the system is decided by the multiply of the excitation PSF and the detection PSF:

detconfocal exPSF PSF PSF= ⋅ . (2)

As both the excitation PSF and the detection PSF are diffraction limited, the PSF of a confocal system is 1.4 times narrower than conventional microscopy, yet still, diffraction limited. Under ideal condition (the pinhole is infinity small), the full-width half maximum (FWHM) of such a system can be described as:

2 2ConfocaldNA

λ= (3)

where NA is the numerical aperture of the imaging lens. It equals to the numerical aperture of the objective in the microscope only when the back aperture is overfilled. λ is the square root of the product of the excitation and detection wavelengths. It reduces to the Abbe diffraction limit when the pinhole is widely open.

In multiphoton microscopy, the nonlinear process is restricted to a spatially and temporally confined zone. For a second-order nonlinear effect, the PSF is also the product of the excitation:

2TPM exPSF PSF= . (4)

where TPMPSF resembles the PSFs of all the second-order effect such as two-photon excited fluorescence (TPEF) or second-order harmonic generation (SHG) signals. Consequently, the resolution can also be expressed with

2 2

exTPMd

NAλ= (5)

As the signal is already self-modulated to a tight second-order focal area, the confocal pinhole in a single-photon microscope is usually not necessary. The FWHM can be described similar to that of Eq.(3), because the PSF is also a product of two excitation PSFs, with the nonlinear ratio of the fluorescent medium. Note that since here λ is the excitation wavelength, which is now almost two-fold that of single-photon excitation, MPM does not give better resolution than that of its single-photon counterparts.



2.2 Stimulated emission process and resolution scaling

To effectively switch-off the peripheral of the fluorescence PSF for super-resolution, a doughnut shaped PSF with wavelength locating on the tail of the fluorescent emission spectrum is overlapped on the excitation PSF. Such kind of far-field intensity distribution can be generated with a 0-2π vortex phase plate. Since the phase distribution has a constant π phase difference at symmetric position along the axis, it produces a first-order Bessel distribution.

For CW excitation and depletion, the fluorescent depletion ratio can be described by [7]

11 /mod satI I

η =+ (6)

The FWHM of the STED microscope can therefore be described as [8]

2 1 /mod sat

dNA I I

λ=+

. (7)

Therefore, the resolution of STED can be increased with the increasing of modI , and the measurement of satI can be used to estimate the resolution that is achievable with the certain STED power. It should be noted that, due to the fact that the intensity profile is inhomogenous inside the focal spot (it takes a Gaussian distribution along lateral as well as axial planes), the theoretical achievable resolution versus the power applied takes the following relationship [9]:

2 1 /mod sat

dNA P P

λα

≈+

. (8)

where α is a modulation factor, and satP is the power required (for a specific objective) to deplete the fluorescence to its half.

0 20 40 60 80 100 120 140 160 180 200 2200.0

0.2

0.4

0.6

0.8

1.0

Inte

nsity

[A. U

.]

Power Intensity(MW/cm2)

ATTO-647 Fitting Crimson Bead Fitting

Figure 1 Saturation intensity measurement for both ATTO 647N and crimson beads, measured with Gaussian distribution.

3. METHODS AND MATERIALS 3.1 STED Instrumentation

The STED system was built based on a home-made confocal imaging system with 635 nm excitation. A Ti:Sapphire laser (Griffin-F, KMLabs, USA) pumped by a 6-Watt DPSS 532nm laser (Finesse-6W, Laser Quantum, UK) was employed as the CW STED source. The output from the laser source is ~800mW. To generate the doughnut PSF for



effective depletion, a vortex 0-2π phase plate (VPP-A, RPC Photonics) was used. We focused the beams into samples using an oil-immersion objective of NA=1.4 (100x, PlanAPO, Zeiss). To obtain a 2-D image, a piezo scanning stage (Nanomax, Thorlabs) was employed to move the specimen. A photo-counting avalanche photodiode (SPCM-AQRH-13-FC, Perkin Elmer) was used to collect the fluorescence signal. The scanning and data collection were performed with a DAQ board (USB-6259, National Instruments), and image collection was accomplished with Imspector (Max-Plank Innovation).

3.2 Microtubule Immunofluorescence

Pt2K were plated the day before fixation at 25% confluency and were fixed with 100% methanol for 10 min at -20 °C and additionally permeabilized with 100% acetone for 2 min at -20 °C. Nonspecific antibody binding was blocked with 5% bovine serum albumin (EMD) in PBS for 30 min at 37 °C. Pt2Ks were then incubated with a primary antibody against alpha tubulin (rabbit polyclonal IgG, Abcam ab18251) for 30 min at 37 °C, washed twice in PBS, and incubated with a secondary antibody (goat anti-rabbit ATTO647N IgG, ATTO-tec) for 30 min at 37 °C, washed twice in PBS, and mounted in Mowiol 4-88 (Sigma).

4. RESULTS

As the measurement of satI can reflect the resulted resolution achievable by an STED system, we have measured the saturation intensity with solutions of ATTO67N and crimson beads. They are measured to be ~17 MW/cm2 for crimson beads at 763 nm, and ~23.8 MW/cm2 for ATTO 647N at 763 nm. The intensities are measured before the 100x objective. Since the maximum STED power of our system is 200 MW/cm2, the estimated resolution achievable by crimson bead is ~70 nm, which is four fold that of the wide-field counterparts. For 760nm STED light, the doughnut area can be estimated to be 2.7x10-9cm2, and the Gaussian shape is only 0.8x10-9cm2, one third that of the doughnut shape [10].

With 20 nm crimson fluorescent beads (Invitrogen), we measured the resolution of our STED system. 10 beads are averaged, and the resolution is 71nm ± 9nm. The result is shown in Figure 2. The comparison showed clearly that the performance of deconvolution is much better with the STED results than the confocal results.

We have also imaged the microtubules of PtK2 cell, as shown in Figure 3. The fine structures can be distinguished from the STED imaging but not in the confocal image.

5. CONCLUSION Ti:Sapphire laser has been widely used in multiphoton microscopy. Here, we demonstrate the application of a Ti:Sapphire oscillator with a modest intensity of 300mW, to realize the CW STED super-resolution nanoscopy. With the imaging of 20 nm nanospheres, we achieved resolution of ~70 nm optical nanoscopy. The cellular STED images revealed the fine structures of the cellular skeletons such as microtubules, which cannot be differentiated by confocal microscopy. This work suggests a general access for the synchronization-free STED super-resolution nanoscopy.

ACKNOWLEDGMENT The authors would like to acknowledge Dr. Katrin Willig, Dr. Benjamine Harke and Dr. Haisen Ta for technical instructions; and Dr. Andreas Schönle for helping with Imspector. PX thanks Prof. Stefan W. Hell for mentoring and training on STED nanoscopy instrumentation. This research is supported by the “973” Major State Basic Research Development Program of China (2011CB809101, 2010CB933901, 2011CB707502), the National Natural Science Foundation of China (61178076), PKU-GT/Emory University BME Seed Grant funded by Wallace H. Coulter Foundation, and seed fund support from Olympus Australia.



HaConu

33QConu

0 100 200 300 400 500 600 70030

60

90

120

150

Distance (nm)

60

90

120

Counts / 0.1m

s

63 nmCou

nts /

0.1

ms

CW STED

Confocal

Figure 2 Resolution measured with 20nm nanospheres.



COMM

0 500 1000 1500 2000

300

350

400

450

250

300

350

Distance (nm)

CW STED

Confocal

Cou

nts /

0.1

ms C

ounts / 0.1ms

Figure 3 The cellular microtubules imaged with (a) confocal and (b) STED. The intensity profile in the inlet of (a) and (b)

are plotted in (c). and the branches can be resolved in the STED results.

REFERENCES

[1] Ding, Y., P. Xi, and Q. Ren, Hacking the optical diffraction limit: Review on recent developments of fluorescence nanoscopy. Chinese Science Bulletin, 2011. 56(18): p. 1857-1876.

[2] Hell, S.W. and J. Wichmann, Breaking the diffraction resolution limit by stimulated emission: stimulated-emission-depletion fluorescence microscopy. Opt. Lett., 1994. 19(11): p. 780-782.

[3] Gustafsson, M.G.L., Nonlinear structured-illumination microscopy: wide-field fluorescence imaging with theoretically unlimited resolution. Proceedings of the National Academy of Sciences of the United States of America, 2005. 102(37): p. 13081.

[4] Betzig, E., et al., Imaging intracellular fluorescent proteins at nanometer resolution. Science, 2006. 313(5793): p. 1642.

[5] Rust, M.J., M. Bates, and X. Zhuang, Sub-diffraction-limit imaging by stochastic optical reconstruction microscopy (STORM). Nature methods, 2006. 3(10): p. 793-796.

[6] Liu, Y., et al., Achieving λ/10 Resolution CW STED Nanoscopy with a Ti: Sapphire Oscillator. PLoS One, 2012. 7(6): p. e40003.

[7] Leutenegger, M., C. Eggeling, and S.W. Hell, Analytical description of STED microscopy performance. Opt. Express, 2010. 18(25): p. 26417-26429.

[8] Westphal, V. and S.W. Hell, Nanoscale resolution in the focal plane of an optical microscope. Physical review letters, 2005. 94(14): p. 143903.

[9] Xie, H., et al., Analytical description of high-aperture STED resolution with 0-2pi vortex phase modulation. 2012: p. (submitted.).

[10] Willig, K.I., et al., STED microscopy with continuous wave beams. Nature Methods, 2007. 4(11): p. 915-918.



PROGRESS IN BIOMEDICAL OPTICS AND IMAGING Vol. 13, No. 42

Volume 8553

Proceedings of SPIE, 1605-7422, v. 8553

SPIE is an international society advancing an interdisciplinary approach to the science and application of light.

Optics in Health Care and Biomedical Optics V Qingming Luo Ying Gu Xingde D. Li Editors 5–7 November 2012 Beijing, China Sponsored by SPIE COS—Chinese Optical Society Cooperating Organizations Tsinghua University (China) • Peking University (China) • Zhejiang University (China) • Beijing Institute of Technology (China) • Beijing University of Posts and Telecommunications (China) University of Science and Technology of China • Tianjin University (China) • Nankai University (China) • Changchun University of Science and Technology (China) • University of Shanghai for Science and Technology (China) • Capital Normal University (China) • Huazhong University of Science and Technology (China) • Beijing Jiaotong University (China) • Shanghai Institute of Optics and Fine Mechanics (China) • Changchun Institute of Optics and Fine Mechanics (China) • Institute of Semiconductors (China) • Institute of Optics and Electronics (China) • Institute of Physics (China) • Shanghai Institute of Technical Physics (China) • China Instrument and Control Society • Optoelectronics Technology Committee, COS (China) • SPIE National Committee in China • Japan Optical Society • Korea Optical Society (Korea, Republic of) • Australia Optical Society • Singapore Optical Society Supporting Organizations CAST—China Association for Science and Technology (China) NSFC—National Nature Science Foundation (China) Published by SPIE

Optics in Health Care and Biomedical Optics V, edited by Qingming Luo, Ying Gu, Xingde D. Li, Proc. of SPIE Vol. 8553, 855301 · © 2012 SPIE · CCC code: 1605-742/12/$18

doi: 10.1117/12.2014549

Proc. of SPIE Vol. 8553 855301-1


The papers included in this volume were part of the technical conference cited on the cover and title page. Papers were selected and subject to review by the editors and conference program committee. Some conference presentations may not be available for publication. The papers published in these proceedings reflect the work and thoughts of the authors and are published herein as submitted. The publisher is not responsible for the validity of the information or for any outcomes resulting from reliance thereon. Please use the following format to cite material from this book: Author(s), "Title of Paper," in Optics in Health Care and Biomedical Optics V, edited by Qingming Luo, Ying Gu, Xingde D. Li, Proceedings of SPIE Vol. 8553 (SPIE, Bellingham, WA, 2012) Article CID Number. ISSN: 1605-7422 ISBN: 9780819493088 Published by SPIE P.O. Box 10, Bellingham, Washington 98227-0010 USA Telephone +1 360 676 3290 (Pacific Time)· Fax +1 360 647 1445 SPIE.org Copyright © 2012, Society of Photo-Optical Instrumentation Engineers. Copying of material in this book for internal or personal use, or for the internal or personal use of specific clients, beyond the fair use provisions granted by the U.S. Copyright Law is authorized by SPIE subject to payment of copying fees. The Transactional Reporting Service base fee for this volume is $18.00 per article (or portion thereof), which should be paid directly to the Copyright Clearance Center (CCC), 222 Rosewood Drive, Danvers, MA 01923. Payment may also be made electronically through CCC Online at copyright.com. Other copying for republication, resale, advertising or promotion, or any form of systematic or multiple reproduction of any material in this book is prohibited except with permission in writing from the publisher. The CCC fee code is 1605-7422/12/$18.00. Printed in the United States of America. Publication of record for individual papers is online in the SPIE Digital Library.

SPIEDigitalLibrary.org

Paper Numbering: Proceedings of SPIE follow an e-First publication model, with papers published first online and then in print and on CD-ROM. Papers are published as they are submitted and meet publication criteria. A unique, consistent, permanent citation identifier (CID) number is assigned to each article at the time of the first publication. Utilization of CIDs allows articles to be fully citable as soon as they are published online, and connects the same identifier to all online, print, and electronic versions of the publication. SPIE uses a six-digit CID article numbering system in which:

The first four digits correspond to the SPIE volume number. The last two digits indicate publication order within the volume using a Base 36 numbering

system employing both numerals and letters. These two-number sets start with 00, 01, 02, 03, 04, 05, 06, 07, 08, 09, 0A, 0B … 0Z, followed by 10-1Z, 20-2Z, etc.

The CID Number appears on each page of the manuscript. The complete citation is used on the first page, and an abbreviated version on subsequent pages. Numbers in the index correspond to the last two digits of the six-digit CID Number.



Contents xiii Symposium Committees xv Conference Committee xix Quantum dot lasers and relevant nanoheterostructures (Plenary Paper) [8552-1] A. E. Zhukov, N. V. Kryzhanovskaya, A. V. Savelyev, A. M. Nadtochiy, E. M. Arakcheeva,

F. I. Zubov, V. V. Korenev, Saint Petersburg Academic Univ. (Russian Federation); M. V. Maximov, Y. M. Shernyakov, M. M. Kulagina, I. A. Slovinskiy, Ioffe Physical-Technical Institute (Russian Federation); D. A. Livshits, Innolume GmbH (Germany); A. Kapsalis, C. Mesaritakis, D. Syvridis, Univ. of Athens (Greece); A. M. Mintairov, Univ. of Notre Dame (United States)

SESSION 1 ADVANCED BIOMEDICAL OPTICAL TECHNIQUES

8553 04 Integrated on-chip lens applied to microfluidic chips (Invited Paper) [8553-3] Y. Zhao, Q. Li, X.-M. Hu, D.-F. Yang, Beijing Institute of Technology (China) 8553 05 Motion compensation of optical mapping signals from rat heart slices (Invited Paper)

[8553-4] B. Stender, Univ. zu Lübeck (Germany); M. Brandenburger, Fraunhofer Research Institution

for Marine Biotechnology (Germany); B. Wang, Z. Zhang, Xi'an Jiaotong Univ. (China); A. Schlaefer, Univ. zu Lübeck (Germany)

SESSION 2 INNOVATIVE OPTICAL IMAGING METHODS I

8553 0A Coherent fiber supercontinuum laser for nonlinear biomedical imaging [8553-9] H. Tu, Y. Liu, Univ. of Illinois at Urbana-Champaign (United States); X. Liu, J. Lægsgaard,

D. Turchinovich, Technical Univ. of Denmark (Denmark); S. A. Boppart, Univ. of Illinois at Urbana-Champaign (United States)

8553 0B Wide field-of-view microscopy with Talbot pattern illumination [8553-10] J. Wu, G. Liu, Shanghai Jiao Tong Univ. (China) and Univ. of Michigan (United States) SESSION 3 PHOTONIC THERAPEUTICS

8553 0D Indirect photobiomodulation in functional networks (Invited Paper) [8553-12] T. C.-Y. Liu, W.-W. Zhu, X.-B. Yang, South China Normal Univ. (China)

iii



SESSION 4 PHOTODYNAMIC THERAPY

8553 0F Advanced optical techniques for monitoring dosimetric parameters in photodynamic therapy (Invited Paper) [8553-15]

B. Li, Z. Qiu, Fujian Normal Univ. (China); Z. Huang, Fujian Normal Univ. (China) and Univ. of Colorado Denver (United States)

8553 0G Efficacy of gallium phthalocyanine as a photosensitizing agent in photodynamic therapy

for the treatment of cancer [8553-16] K. Maduray, B. Odhav, Durban Univ. of Technology (South Africa) 8553 0H Efficient photodynamic therapy against Staphylococcus aureus using [Ru(bpy)2(dppn)]2+: a

novel cationic photosensitizer [8553-17] Y. Wang, Chinese People's Liberation Army General Hospital (China) and Nankai Univ.

(China); Y. Wang, Y. Gu, Chinese People's Liberation Army General Hospital (China) 8553 0J Polyethylene glycol-functionalized bis(arylidene)cycloalkanone photosensitizers for two-

photon excited photodynamic therapy [8553-19] Q. Zou, Technical Institute of Physics and Chemistry (China) and Graduate Univ. of the

Chinese Academy of Sciences (China); H. Zhao, Chinese People's Liberation Army General Hospital (China); Y. Zhao, Technical Institute of Physics and Chemistry (China); Y. Wang, Y. Gu, Chinese People's Liberation Army General Hospital (China); F. Wu, Technical Institute of Physics and Chemistry (China)

SESSION 5 INNOVATIVE OPTICAL IMAGING METHODS II

8553 0O Design of an affordable fluorescence confocal laser scanning microscope for medical diagnostics [8553-24]

C. Bechtel, Technische Univ. Dresden (Germany); J. Knobbe, H. Grüger, H. Lakner, Fraunhofer-Institut für Photonische Mikrosysteme (Germany)

8553 0P Multiview hyperspectral topography of tissue structural and functional characteristics

[8553-25] S. Zhang, Univ. of Science and Technology of China (China) and The Ohio State Univ.

(United States); P. Liu, Univ. of Science and Technology of China (China); J. Huang, The Ohio State Univ. (United States); R. Xu, Univ. of Science and Technology of China (China) and The Ohio State Univ. (United States)

SESSION 6 OPTICAL COHERENCE TOMOGRAPHY I

8553 0Q Recent advances in optical coherence tomography (Invited Paper) [8553-26] Z. Ding, C. Wang, Y. Shen, L. Huang, L. Wu, C. Du, Zhejiang Univ. (China) 8553 0S Phantom testing of a novel endoscopic OCT probe: a prelude to clinical in-vivo laryngeal

use [8553-28] T. Tatla, J. Y. Pang, Northwick Park Hospital (United Kingdom); R. Cernat, G. Dobre, Univ. of

Kent (United Kingdom); P. J. Tadrous, Northwick Park Hospital (United Kingdom); A. Bradu, Univ. of Kent (United Kingdom); G. Gelikonov, V. Gelikonov, Institute of Applied Physics (Russian Federation); A. G. Podoleanu, Univ. of Kent (United Kingdom)

iv



SESSION 7 OPTICAL COHERENCE TOMOGRAPHY II

8553 0V In vivo integrated photoacoustic ophthalmoscopy, optical coherence tomography, and scanning laser ophthalmoscopy for retinal imaging [8553-32]

W. Song, Harbin Institute of Technology (China) and Northwestern Univ. (United States); R. Zhang, Harbin Institute of Technology (China); H. F. Zhang, Q. Wei, Northwestern Univ. (United States); W. Cao, Harbin Institute of Technology (China) and The Pennsylvania State Univ. (United States)

SESSION 8 PHOTONIC DIAGNOSTICS I

8553 0W Studying the role of macrophages in circulating prostate cancer cells by in vivo flow cytometry (Invited Paper) [8553-33]

X. Cui, J. Guo, Fudan Univ. (China); Z. Gu, Shanghai Jiao Tong Univ. (China); X. Wei, Fudan Univ. (China) and Shanghai Jiao Tong Univ. (China)

8553 0Z Simulating the demyelination of a nerve fiber by action potential encoded second

harmonic generation [8553-36] H. Yang, Z. Luo, X. Chen, Y. Huang, S. Xie, Fujian Normal Univ. (China) SESSION 9 PHOTONIC DIAGNOSTICS II

8553 11 Identification of non-neoplastic and neoplastic gastric polyps using multiphoton microscopy (Invited Paper) [8553-38]

S. Jiang, Fujian Normal Univ. (China); D. Kang, M. Xu, Fujian Medical Univ. (China); X. Zhu, S. Zhuo, J. Chen, Fujian Normal Univ. (China)

8553 12 Collagen fiber spatial orientation mapping using polarization-sensitive SHG microscopy

[8553-39] V. A. Hovhannisyan, P.-S. Hu, C.-Y. Dong, National Taiwan Univ. (Taiwan) 8553 13 Measuring intracellular calcium dynamics of HeLa cells exposed to nitric oxide by

microplate fluorescence reader [8553-40] Y. Huang, J. Chen, H. Yang, L. Zheng, Y. Wang, H. Li, S. Xie, Fujian Normal Univ. (China) 8553 14 Metabolic changes of cultured DRG neurons induced by adenosine using confocal

microscopy imaging [8553-41] L. Zheng, Y. Huang, J. Chen, Y. Wang, H. Yang, Y. Zhang, S. Xie, Fujian Normal Univ. (China) SESSION 10 PHOTONIC DIAGNOSTICS III

8553 18 Nonlinear optical imaging characteristics of colonic adenocarcinoma using multiphoton microscopy [8553-45]

N. Liu, R. Chen, H. Li, J. Chen, Fujian Normal Univ. (China)

v



8553 19 Molecular application of spectral photoacoustic imaging in pancreatic cancer pathology [8553-46]

M. Lakshman, C. Hupple, VisualSonics Inc. (Canada); I. Lohse, Ontario Cancer Institute (Canada) and Campbell Family Cancer Research Institute (Canada); D. Hedley, Ontario Cancer Institute (Canada), Campbell Family Cancer Research Institute (Canada), and Univ. of Toronto (Canada); A. Needles, C. Theodoropoulos, VisualSonics Inc. (Canada)

SESSION 11 INNOVATIVE MICROSCOPY IMAGING METHOD

8553 1A Dynamics of two-photon two-color transitions in flurophores excited by femtosecond laser pulses (Invited Paper) [8553-47]

P. S. Shternin, A. G. Smolin, O. S. Vasyutinskii, Ioffe Insitute (Russian Federation); S. Denicke, S. Herbrich, K.-H. Gericke, Technische Univ. Braunschweig (Germany)

8553 1B CW STED nanoscopy with a Ti:Sapphire oscillator [8553-49] Y. Liu, Shanghai Jiao Tong Univ. (China) and Peking Univ. (China); H. Xie, Peking Univ.

(China); E. Alonas, P. J. Santangelo, Georgia Institute of Technology and Emory Univ. School of Medicine (United States); D. Jin, Macquarie Univ. (Australia); P. Xi, Peking Univ. (United States)

8553 1C LOSOM: phase relief imaging can be achieved with confocal system [8553-50] T. Peng, Peking Univ. (China) and Xi'an Univ. of Technology (China); H. Xie, Y. Ding, Peking

Univ. (China); Y. Lu, D. Jin, Macquarie Univ. (Australia); P. Xi, Peking Univ. (China) 8553 1D Design of a real-time portable confocal scanning laser microscope [8553-52] X. Yang, Peking Univ. (China) and Xi'an Univ. of Technology (China); Y. Zhao, Peking Univ.

(China); G. Yin, Shanghai Bandweave Technologies Co. Ltd. (China); H. Li, Peking Univ. (China) and Xi'an Univ. of Technology (China); T. Wang, P. Xi, Peking Univ. (China)

SESSION 12 MUTIMODE IMAGING

8553 1E Photo-acoustic excitation and detection of guided ultrasonic waves in bone samples covered by a soft coating layer [8553-53]

Z. Zhao, Univ. of Oulu (Finland); P. Moilanen, Univ. of Jyväskylä (Finland); P. Karppinen, Univ. of Helsinki (Finland); M. Määttä, Univ. of Oulu (Finland); T. Karppinen, E. Hæggström, Univ. of Helsinki (Finland); J. Timonen, Univ. of Jyväskylä (Finland); R. Myllylä, Univ. of Oulu (Finland)

8553 1F ICG-loaded microbubbles for multimodal billiary imaging in cholecystectomy [8553-54] R. Qin, S. Melvin, The Ohio State Univ. (United States); R. X. Xu, The Ohio State Univ. (United

States) and Univ. of Science and Technology of China (China) 8553 1G Multimodal imaging of ischemic wounds [8553-55] S. Zhang, Univ. of Science and Technology of China (China) and The Ohio State University

(United States); S. Gnyawali, J. Huang, The Ohio State Univ. (United States); P. Liu, Univ. of Science and Technology of China (China); G. Gordillo, C. K. Sen, The Ohio State Univ. (United States); R. Xu, Univ. of Science and Technology of China (China) and The Ohio State Univ. (United States)

vi



8553 1H Novel coaxial atomization processes for microfabrication of multi-layered biodegradable microcapsules [8553-56]

T. Si, Univ. of Science and Technology of China (China); L. Zhang, The Ohio State Univ. (United States); G. Li, Univ. of Science and Technology of China (China); R. Xu, Univ. of Science and Technology of China (China) and The Ohio State Univ. (United States)

SESSION 13 OPTICS IMAGING ALGORITHMS AND ANALYSIS I

8553 1I Electromagnetic scattering from biological tissue [8553-57] Z. Tong, O. Korotkova, Univ. of Miami (United States) 8553 1J 3D reconstruction for endoscopic environment based on optical tracker [8553-58] B. Yang, Y. Zhou, X. Hu, J. Lin, Q. Xing, Beijing Institute of Technology (China) 8553 1L Photoacoustic imaging: a potential new tool for arthritis (Invited Paper) [8553-128] X. Wang, Univ. of Michigan Health System (United States) SESSION 14 OPTICS IMAGING ALGORITHMS AND ANALYSIS II

8553 1O Investigating the backscattering characteristics of individual normal and cancerous cells based on experimentally determined three-dimensional refractive index distributions [8553-64]

W.-C. Hsu, J.-W. Su, C.-C. Chang, K.-B. Sung, National Taiwan Univ. (Taiwan) 8553 1P Cost-effective approaches for high-resolution bioimaging by time-stretched confocal

microscopy at 1µm [8553-65] T. T. W. Wong, Y. Qiu, A. K. S. Lau, J. Xu, A. C. S. Chan, K. K. Y. Wong, K. K. Tsia, The Univ. of

Hong Kong (Hong Kong, China) 8553 1Q Quantitative interferometric microscopy: tool for phase imaging from 2D to 3D [8553-66] S. Wang, L. Xue, J. Lai, Y. Song, Z. Li, Nanjing Univ. of Science and Technology (China) SESSION 15 SPECTROSCOPY FOR BIOMEDICAL APPLICATION

8553 1R Fast reconstruction of Raman spectra from narrow-band measurements based on Wiener estimation [8553-67]

S. Chen, Y. H. Ong, Q. Liu, Nanyang Technological Univ. (Singapore) 8553 1S Evaluation of human dentine demineralization of yellow race by Raman spectra [8553-68] Z. Zhan, W. Guo, H. Liu, X. Zhang, S. Xie, Fujian Normal Univ. (China) 8553 1T Assessment of skin flap viability using visible diffuse reflectance spectroscopy and auto-

fluorescence spectroscopy [8553-69] C. Zhu, S. Chen, Nanyang Technological Univ. (Singapore); C. H.-K. Chui, Singapore

General Hospital (Singapore); Q. Liu, Nanyang Technological Univ. (Singapore)

vii



8553 1U Characterization and differentiation of normal and abnormal semen samples using micro-Raman spectroscopy [8553-70]

Z. Huang, X. Chen, Fujian Normal Univ. (China); J. Chen, Fujian Provincial Hospital (China); Y. Li, J. Lei, R. Chen, Fujian Normal Univ. (China)

8553 1V Brain cancer probed by native fluorescence and stokes shift spectroscopy [8553-71] Y. Zhou, Chinese People's Liberation Army General Hospital (China); C. Liu, The City

College of New York, CUNY (United States); Y. He, Beijing Normal Univ. (China); Y. Pu, The City College of New York, CUNY (United States); Q. Li, W. Wang, BeiHang Univ. (China); R. R. Alfano, The City College of New York, CUNY (United States)

SESSION 16 LASER-TISSUE INTERACTION

8553 1X Rabbit electroretinograms evoked by 632.8nm laser flash stimuli [8553-74] Z.-F. Yang, Beijing Institute of Radiation Medicine (China); H.-X. Chen, People's Liberation

Army General Hospital (China); J.-R. Wang, B.-L. Guan, Beijing Institute of Radiation Medicine (China); G.-Y. Yu, People's Liberation Army General Hospital (China); X.-N. Zhang, W.-Y. Zhang, J.-G. Yang, Beijing Institute of Radiation Medicine (China)

8553 1Y The threshold of vapor channel formation in water induced by pulsed CO2 laser [8553-75] W. Guo, X. Zhang, Z. Zhan, S. Xie, Fujian Normal Univ. (China) 8553 1Z Mechanisms of interaction between very high-frequency photoacoustic waves and the

skin [8553-76] G. F. F. Sá, C. Serpa, L. G. Arnaut, Univ. de Coimbra (Portugal) POSTER SESSION

8553 20 A method of simulating polarization-sensitive optical coherence tomography based on a polarization-sensitive Monte Carlo program and a sphere cylinder birefringence model [8553-63]

D. Chen, N. Zeng, C. Liu, Key Lab. for Minimal Invasive Medical Technologies (China); H. Ma, Key Lab. for Minimal Invasive Medical Technologies (China) and Tsinghua Univ. (China)

8553 21 Temperature changes in the pulp chamber during dentin ablation with Er:YAG laser

[8553-73] X. Zhang, H. Zhao, Z. Zhan, W. Guo, S. Xie, Fujian Normal Univ. (China) 8553 22 Second harmonic generation imaging of skin wound healing and scarring in a rabbit ear

model [8553-79] Y. Tang, Fujian Normal Univ. (China) and Fujian Medical Univ. (China); X. Zhu, Fujian Normal

Univ. (China); S. Xiong, Fujian Medical Univ. (China); J. Chen, Fujian Normal Univ. (China) 8553 23 Study of ABO blood types by combining membrane electrophoresis with surface-

enhanced Raman spectroscopy [8553-80] J. Wang, J. Lin, Z. Huang, Fujian Normal Univ. (China); L. Sun, First Hospital of Fuzhou

(China); Y. Shao, Shenzhen Univ. (China); P. Lu, W. Shi, J. Lin, R. Chen, Fujian Normal Univ. (China)

viii



8553 25 Surface-enhanced Raman spectroscopy study of radix astragali based on soxhlet extractor [8553-82]

P. Lu, J. Lin, N. Liu, Fujian Normal Univ. (China); Y. Shao, Shenzhen Univ. (China); J. Wang, W. Shi, J. Lin, R. Chen, Fujian Normal Univ. (China)

8553 26 Photo-induced electron transfer between dendritic zinc(II) phthalocyanine bearing

carboxylic terminal groups and methyl viologen [8553-83] Y. Wang, J. Chen, L. Huang, S. Xie, H. Yang, Y. Peng, Fujian Normal Univ. (China) 8553 27 Cutaneous pain effects induced by Nd:YAG and CO2 laser stimuli [8553-84] J.-R. Wang, Beijing Institute of Radiation Medicine (China); G.-Y. Yu, People's Liberation

Army General Hospital (China); Z.-F. Yang, Beijing Institute of Radiation Medicine (China); H.-X. Chen, People's Liberation Army General Hospital (China); D.-D. Hu, Beijing Institute of Radiation Medicine (China); X.-B. Zou, People's Liberation Army General Hospital (China)

8553 28 Distinction of gastric cancer tissue based on surface-enhanced Raman spectroscopy

[8553-85] J. Ma, H. Zhou, L. Gong, S. Liu, Z. Zhou, Ocean Univ. of China (China); W. Mao, Qingdao

Municipal Hospital (China); R. Zheng, Ocean Univ. of China (China) 8553 29 Error analysis of image acquisition by moving objective lens [8553-86] H. Xie, H. Chen, Y. Cai, F. Yang, Guangxi Univ. (China) 8553 2A Reverse propagation properties of light wave in tapered micro-nano fiber for cell

endoscopy [8553-87] D. Zhou, J. Zhong, Jinan Univ. (China) 8553 2C Polyion complex micelles incorporating poly (aryl benzyl ether) dendritic phthalocyanine:

effective photosensitizers for enhanced photodynamic therapy [8553-89] K. Chen, M. Yu, H. Zhang, D. Ma, S. Pang, W. Huang, Y. Peng, Fujian Normal Univ. (China) 8553 2D Ultra-long scan depth optical coherence tomography for imaging the anterior segment of

human eye [8553-90] D. Zhu, M. Shen, L. Leng, Wenzhou Medical College (China) 8553 2G Quadratic trianqular element for diffuse optical tomography [8553-93] X. Zhang, Y. Deng, J. Xu, Z. Luo, H. Gong, Q. Luo, Huazhong Univ. of Science and

Technology (China) 8553 2J Photoacoustic measurement for glucose solution concentration based on tunable pulsed

laser induced ultrasound [8553-96] Z. Ren, G. Liu, Z. Huang, D. Zhao, Jiangxi Science and Technology Normal Univ. (China) 8553 2L Expansion of scattered phase matrix based on Zernike polynomials [8553-98] H. Ye, Z. Gao, Q. Wang, K. Bao, X. Yang, Nanjing Univ. of Science and Technology (China) 8553 2M Optical-resolution photoacoustic microscopy for imaging blood vessels in vivo [8553-99] Y. Yuan, South China Normal Univ. (China) 8553 2N Optical characters of prostate using nonlinear optical microscopy [8553-100] S. Wu, H. Li, X. Zhang, Y. Wang, D. Peng, Fujian Normal Univ. (China)

ix



8553 2P Effect of apertures in ultrasound-modulated optical tomography with photomultiplier tube [8553-102]

L. Zhu, S. Ran, Z. Lin, H. Li, Fujian Normal Univ. (China) 8553 2Q The tapered-tip single fiber optical tweezers and its multi-trapping [8553-103] X. Guo, Z. Liu, Y. Zhao, L. Yuan, Harbin Engineering Univ. (China) 8553 2R Scattering properties of normal and cancerous tissues from human stomach based on

phase-contrast microscope [8553-104] H. Zhang, Z. Li, H. Li, Fujian Normal Univ. (China) 8553 2S Retrieval of atmospheric visibility from multi-axis differential optical absorption

spectroscopy [8553-105] H. J. Zhou, Univ. of Science and Technology of China (China) and Anhui Institute of Optics

and Fine Mechanics (China); W. Q. Liu, F. Q. Si, Anhui Institute of Optics and Fine Mechanics (China)

8553 2T Monte Carlo simulation of photon coherent behavior in half Iinfinite turbid medium by

scaling method [8553-106] L. Lin, Guangdong Medical College (China); M. Zhang, H. Liu, Dongguan Univ. of

Technology (China) 8553 2U In vivo detection of hemoglobin oxygen saturation and carboxyhemoglobin saturation

variations with photoacoustic microscopy [8553-107] Z. Chen, S. Yang, D. Xing, South China Normal Univ. (China) 8553 2V Photoacoustic imaging of prostate cancer using cylinder diffuse radiation [8553-108] W. Xie, L. Li, Z. Li, H. Li, Fujian Normal Univ. (China) 8553 2W Realization of the ergonomics design and automatic control of the fundus cameras

[8553-109] C. Zeng, Z. Xiao, S. Deng, X. Yu, Guilin Univ. of Electronic Technology (China) 8553 2Y Study the effect of temperature on optical properties of biological tissue-simulating

phantom based on OCT [8553-111] Y. He, H. Li, Fujian Normal Univ. (China) 8553 2Z Miniature interferometer for refractive index measurement in microfluidic chip [8553-112] M. Chen, Univ. of Shanghai for Science and Technology (China); M. Geiser, F. Truffer, Univ.

of Applied Sciences Western Switzerland (Switzerland); C. Song, Univ. of Shanghai for Science and Technology (China)

8553 30 Study for noninvasive determination of optical properties of bio-tissue using spatially

resolved diffuse reflectance [8553-113] D. Peng, Fujian Normal Univ. (China) and Jimei Univ. (China); H. Li, Fujian Normal Univ.

(China) 8553 31 Development of an in situ magnetic beads based RT-PCR method for

electrochemiluminescent detection of rotavirus [8553-114] F. Zhan, X. Zhou, South China Normal Univ. (China)

x

Proc. of SPIE Vol. 8553 855301-10


8553 32 ERK-dependent activation of Sp1 is required for low-power laser irradiation-induced vascular endothelial cell proliferation [8553-115]

J. Feng, D. Xing, South China Normal Univ. (China) 8553 33 Iterative reconstruction for bioluminescence tomography with total variation regularization

[8553-117] W. Jin, Peking Univ. (China); Y. He, Beijing Aerospace Control Ctr. (China) 8553 34 Imaging the morphological change of tissue structure during the early phase of

esophageal tumor progression using multiphoton microscopy [8553-118] J. Xu, Fujian Normal Univ. (China); D. Kang, M. Xu, Fujian Medical Univ. (China); X. Zhu,

S. Zhuo, J. Chen, Fujian Normal Univ. (China) 8553 36 Amplification-free detection of miRNA via an ECL chips system [8553-120] W. Liu, X. Zhou, South China Normal Univ. (China) 8553 37 Label-free and sensitive fluorescence detection of nucleic acid, based on combination of

a graphene oxid /SYBR green I dye platform and polymerase assisted signal amplification [8553-121]

X. Zhu, D. Xing, South China Normal Univ. (China) 8553 39 Photoacoustic spectroscopic differences between normal and malignant thyroid tissues

[8553-123] L. Li, W. Xie, H. Li, Fujian Normal Univ. (China) 8553 3A Ex-vivo endoscopic laryngeal cancer imaging using two forward-looking fiber optic

scanning endoscope probes [8553-124] R. Cernat, Univ. of Kent (United Kingdom); T. Tatla, J.-Y. Pang, P. J. Tadrous, Northwick Park

Hospital (United Kingdom); G. Gelikonov, V. Gelikonov, Institute of Applied Physics (Russian Federation); Y.-Y. Zhang, Johns Hopkins Univ. (United States); A. Bradu, Univ. of Kent (United Kingdom); X. D. Li, Johns Hopkins Univ. (United States); A. G. Podoleanu, Univ. of Kent (United Kingdom)

8553 3B Glucose and temperature sensitive luminescence ZnCdS nanoparticles [8553-125] V. I. Kochubey, E. K. Volkova, J. G. Konyukhova, N.G. Chernyshevsky Saratov State Univ.

(Russian Federation) 8553 3C Characterization of muscle stretching and damage using polarization-sensitive optical

coherence tomography (PS-OCT) [8553-126] D. Chen, N. Zeng, C. Liu, H. Ma, Tsinghua Univ. (China) Author Index

xi

Proc. of SPIE Vol. 8553 855301-11


Proc. of SPIE Vol. 8553 855301-12


Symposium Committees

General Chairs

Eustace L. Dereniak, College of Optical Sciences, The University of Arizona (United States) Bingkun Zhou, Tsinghua University (China)

General Cochairs

Arthur Chiou, National Yang-Ming University (Taiwan, China) Zhizhan Xu, Shanghai Institute of Optics and Fine Mechanics (China) Jianlin Cao, China Ministry of Science and Technology (China) Junhao Chu, Shanghai Institute of Technical Physics (China)

Technical Program Chairs

Songlin Zhuang, Shanghai University of Science and Technology (China)

Xingde Li, Johns Hopkins University (United States)

Technical Program Cochairs

Qiming Wang, Institute of Semiconductors (China) Xu Liu, Zhejiang University (China) Daoyin Yu, Tianjin University (China) Qihuang Gong, Peking University (China) Tianchu Li, National Institute of Metrology (China) Wei Huang, Nanjing University of Posts and Telecommunications (China)

Local Organizing Committee Chair

Guangcan Guo, University of Science and Technology of China (China)

xiii

Proc. of SPIE Vol. 8553 855301-13


Local Organizing Committee Cochairs

Guoqiang Ni, Beijing Institute of Technology (China) Shusen Xie, Fujian Normal University (China) Xiaomin Ren, Beijing University of Posts and Telecommunications

(China) Ying Gu, People’s Liberation Army General Hospital (China) Huilin Jiang, Changchun University of Science and Technology (China)

General Secretary

Qihuang Gong, Peking University (China)

Local Organizing Committee

Yan Li, Chinese Optical Society/Peking University (China) Zhiping Zhou, Peking University (China) Changhe Zhou, Shanghai Institute of Optics and Fine Mechanics

(China) Qingming Luo, Huazhong University of Science and Technology

(China) Chongxiu Yu, Beijing University of Posts and Telecommunications

(China) Hongda Chen, Institute of Semiconductors (China) Yongtian Wang, Beijing Institute of Technology (China) Yiping Cui, Southeast University (China) Xuping Zhang, Nanjing University (China) Feijun Song, Daheng Corporation (China) Cunlin Zhang, Capital Normal University (China) Yanting Lu, Nanjing University (China) Yuejin Zhao, Beijing Institute of Technology (China) Chunqing Gao, Beijing Institute of Technology (China) Tiegen Liu, Tianjin University (China) Xiaocong Yuan, Nankai University (China) Weimin Chen, Chongqing University (China) Zhongwei Fan, Academy of Optoelectronics (China) Hanyi Zhang, Tsinghua University (China) Lan Wu, Zhejiang University (China) Yongsheng Zhang, University of Science and Technology of China

(China) Hong Yang, Peking University (China) Xiaoying Li, Tianjin University (China) Lin Zhai, Chinese Optical Society (China)

xiv

Proc. of SPIE Vol. 8553 855301-14


Conference Committee

Conference Chairs

Qingming Luo, Huazhong University of Science and Technology

(China)

Ying Gu, Chinese People’s Liberation Army General Hospital (China)

Xingde D. Li, Johns Hopkins University (United States)

Conference Program Committee

Jing Bai, Tsinghua University (China)

Stephen A. Boppart, University of Illinois at Urbana-Champaign

(United States)

Wei R. Chen, University of Central Oklahoma (United States)

Yu Chen, University of Maryland, College Park (United States)

Linhong Deng, Chongqing University (China)

Zhihua Ding, Zhejiang University (China)

Qiyong Gong, West China Hospital of Sichuan University, West China

School of Medicine (China)

Hui Li, Fujian Normal University (China)

Hong Liu, The University of Oklahoma (United States)

Hui Ma, Tsinghua University (China)

Atsushi Maki, Hitachi, Ltd. (Japan)

Yingtian Pan, Stony Brook University (United States)

Paras N. Prasad, University at Buffalo (United States)

Yuwen Qin, National Natural Science Foundation (United States)

Qiushi Ren, Peking University (China)

Jie Tian, Institute of Automation (China)

Valery V. Tuchin, N.G. Chernyshevsky Saratov State University

(Russian Federation)

Lihong V. Wang, Washington University in St. Louis (United States)

Ruikang K. Wang, University of Washington (United States)

Xun-Bin Wei, Shanghai Jiao Tong University (China)

Xujie Xia, Affiliated First People's Hospital, Shanghai Jiao Tong

University (China)

Da Xing, South China Normal University (China)

Kexin Xu, Tianjin University (China)

Yudong Zhang, Institute of Optics and Electronics (China)

Zhenxi Zhang, Xi'an Jiaotong University (China)

Dan Zhu, Huazhong University of Science and Technology (China)

xv

Proc. of SPIE Vol. 8553 855301-15


Session Chairs

1 Advanced Biomedical Optical Techniques

Xingde Li, Johns Hopkins University (United States)

2 Innovative Optical Imaging Methods I



3 Photonic Therapeutics

Ying Gu, Chinese People’s Liberation Army General Hospital (China)

4 Photodynamic Therapy

Wei R. Chen, University of Central Oklahoma (United States)

5 Innovative Optical Imaging Methods II

Ronald Xu, The Ohio State University (United States)

6 Optical Coherence Tomography I



7 Optical Coherence Tomography II

Xingde D. Li, Johns Hopkins University (United States)

8 Photonic Diagnostics I


9 Photonic Diagnostics II


10 Photonic Diagnostics III

Buhong Li, Fujian Normal University (China)

11 Innovative Microscopy Imaging Method


12 Mutimode Imaging

Qin Li, Beijing Institute of Technology (China)

13 Optics Imaging Algorithms and Analysis I

Xincheng Yao, The University of Alabama at Birmingham

(United States)

14 Optics Imaging Algorithms and Analysis II


xvi

Proc. of SPIE Vol. 8553 855301-16


15 Spectroscopy for Biomedical Application

Dan Zhu, Huazhong University of Science and Technology (China)

16 Laser-Tissue Interaction

Tianhong Dai, Massachusetts General Hospital (United States)

xvii

Proc. of SPIE Vol. 8553 855301-17


Proc. of SPIE Vol. 8553 855301-18


Quantum dot lasers and relevant nanoheterostructures

Alexey E. Zhukov*a, Natalia V. Kryzhanovskayaa, Artem V. Savelyeva, Alexey M. Nadtochiya, Ekaterina M. Arakcheevaa, Fedor I. Zubova, Vladimir V. Koreneva, Mikhail V. Maximovb, Yuri M. Shernyakovb, Marina M. Kulaginab, Ilia A. Slovinskiyb, Daniil A. Livshitsc, Alexandros Kapsalisd,

Charis Mesaritakisd, Dimitris Syvridisd, Alexander Mintairove

aSt. Petersburg Academic University, Khlopina 8(3), St Petersburg, Russia 194021; bIoffe Physical-Techical Institute, Politekhnicheskaya 26, St Petersburg, Russia 194021; cInnolume GmbH, Konrad-

Adenauer-Allee 11, Dortmund, Germany 44263; dUniversity of Athens, Athens, Greece 15784; eUniversity of Notre Dame, 275 Fitzpatrick Hall, Notre Dame, IN 46556, USA

ABSTRACT

Spectral and power characteristics of QD stripe lasers operating in two-state lasing regime have been studied in a wide range of operation conditions. It was demonstrated that neither self-heating nor increase of the homogeneous broadening are responsible for quenching of the ground-state lasing beyond the two-state lasing threshold. It was found that difference in electron and hole capture rates strongly affects light-current curve. Modulation p-type doping is shown to enhance the peak power of GS lasing transition. Microring and microdisk structures (D = 4–9 μm) comprising 1.3 μm InAs/InGaAs quantum dots have been fabricated and studied by µ-PL and NSOM. Ground-state lasing was achieved well above root temperature (up to 380 K). Effect of inner diameter on threshold characteristics was evaluated.

Keywords: Quantum dots, semiconductor laser, microring resonator, two-state lasing

1. INTRODUCTION For various applications, including optical data transmission, pumping of Raman amplifiers, aesthetic laser surgery, etc, efficient lasers operating around 1.3 μm are requested. Lasers based on self-organized InAs/InGaAs quantum dots (QDs) offer an attractive combination of the required wavelength with extremely low threshold current density and high characteristic temperature. However, at sufficiently high currents a shorter-wavelength (λ ~ 1.2μm) band caused by the first excited-state (ES1) transition appears in the spectrum1. Such a behavior is now referred to as two-state lasing. For a majority of applications two-state lasing has to be suppressed whereas the GS spectral component of the lasing spectrum has to be maximized. Analysis of QD laser behavior based on rate2 and master3 equations predicts that optical power of the GS component reaches its maximal value at threshold of the two-state lasing and then persists. However a number of experimental facts revealed that the GS component declines down to its complete quenching4,5 due probably to laser self-heating in CW regime4 and/or increase of homogeneous broadening5 have been proposed. To clarify possible reasons of the GS lasing quenching we studied spectral and light-current characteristics of broad-area QD lasers.

Microdisks and microrings optical resonators comprising a III-V active region are promising candidates for light emitters to be integrated with silicon photonic circuits. Owing to a combination of a compact size and a high Q-factor, which can be achieved in such structures, ultralow threshold operation is expected. Although the majority of whispering gallery mode (WGM) resonators has been contained quantum-well active region composed of InP-based materials6, QDs may have certain advantages. These include attainability of 1.3 μm emission in GaAs-based structures with high refractive index contrast, low temperature sensitivity, suppressed sidewall recombination rates7, making it possible to achieve lasing in resonators of small diameter. Since the first report8 on QD microdisk laser capable of operating at 77K, significant progress has been made toward high-temperature lasing. In particular, room-temperature lasing has been reported to date for microdisks of few microns in diameter9, whereas for relatively large microrings (35-85 μm) lasing has been recently extended up to 50oC10. In the present work we demonstrate ground-state lasing up to 107oC for optically pumped microring lasers (MRLs) having an outer diameter as small as 6-7 μm.

*[email protected]; phone 7 812 4488594; fax 7 812 4486994; www.spbau.ru

Plenary Paper

Semiconductor Lasers and Applications V, edited by Ning Hua Zhu, Jinmin Li, Frank H. Peters, Changyuan Yu,Proc. of SPIE Vol. 8552, 855202 · © 2012 SPIE · CCC code: 0277-786/12/$18 · doi: 10.1117/12.2009055


xix

Proc. of SPIE Vol. 8553 855301-19


12A

l0A

8A

5A

3A

GS

1160 1180 1200 1220 1240 1260 1280

Wavelength, nm

GS

JES1 i

fffth/

/

4 ' 6 8

Current, A

10 12 14

2. TWO-STATE LASING AND ITS SUPPRESSION IN QD LASERS 2.1 Quenching of GS spectral component

Epitaxial structures comprising a single plane or multiple planes of InAs/InGaAs QDs were grown by molecular beam epitaxy. Stripe lasers of various cavity lengths were tested in pulse regime (300ns @ 2 kHz) on temperature-stabilized heatsink. An evolution of the lasing spectrum with increasing the pump current is shown in Figure 1,a for a 4-mm-long single-QD-plane laser at 17oC. The corresponding light-current characteristics (total output power and optical power of GS and ES1 spectral components of the spectrum) are presented in Figure 1,b. The ES1 band (around 1.18 μm) appears in the spectrum at approximately 3 A whereas the GS component reaches its maximum at 5A, well beyond the onset of two-state lasing. A complete quenching of the GS lasing is observed at 12 A.

Figure 1. Lasing spectra at different currents (a); laser power (b): dashed-dotted curve – total (GS+ES1), solid curve – ground-state component (GS), dashed curve – first excited-state component (ES1).

As it is seen in Figure 1,a the GS band is split into two peaks (~1.254 and ~1.262 nm). According to M. Sugawara et al5 this splitting can be attributed to the homogenous broadening of the QD optical transition. They also suggested that the GS lasing quenching at high currents could be explained by increase of the homogenous broadening. In spite of this we found that the splitting is practically unchanged (6.5 ± 0.4 meV) as current increases up to 12 A. Therefore, the quenching can not be associated with the aforementioned reason. Moreover, spectral positions of the both GS peaks also remain very stable so that the current-induced red shift is only 0.4 nm. Such a shift corresponds to a negligible temperature increment of about 1oC which can not itself lead to suppression of the GS lasing because in this particular laser diode the GS lasing at low currents can be observed up to 68oC. Thus, the GS lasing quenching at high currents can not be attributed to self-heating of the active region as well.


xx

Proc. of SPIE Vol. 8553 855301-20


5 10

Current, A

15

104

''bo 103N'--'i-iN

l02h=1

h=0.5C)

NO

GS+ES1

GS

10102 _1 1

Electron capture rate gec, ns

2.2 Effect of difference in electron and hole relaxation rates

More sophisticated model that does not imply either the homogeneous broadening or self-heating effect is based on assumption of the asymmetry in charge carrier distribution in a QD11. Energy separation of ground- and excited-state energy levels of holes is much smaller than kT that leads to a nearly equal probability of occupation of the hole levels. As a result, there is a competition for the “joint holes” between electrons of the ground-state and the excited-state levels. Because the ES1 electron level has a higher degeneracy as compared to the GS level, in the regime of two-state lasing the holes are effectively swept out from QDs because of their recombination with ES1 electrons. In its turn this leads to the quenching of the GS lasing as the pump current grows.

Figure 2. L-I curves for ground-state component (a): circles – experiment; lines – calculation for different ratio of hole-to-electron relaxation rates (h). Operation diagram of QD laser: heavy lines separates regions of different lasing regimes (NL – no lasing, GS – pure ground-state lasing, GS+ES1 – two-state lasing, ES1 – pure excited-state lasing); thin lines correspond to different h values.

However, we found that the observed experimental data can not be quantitatively described if one takes into account only the above-mentioned asymmetry. Reasonable agreement between modeling results and experiment was achieved under assumption that electron and hole relaxation rates into QDs are different. More precisely, we assumed that the hole capture is slower than the electron one which makes the competition for holes more pronounced and leads to complete quenching of the GS lasing at lower pumps. Figure 2,a shows the calculated evolution of the GS power with the pump current. The results are shown for different ratio of the hole-to-electron relaxation rates h which is assumed to be independent of the injection rate. The best agreement of the model results with the experiment is found for h = 0.75. Lower rate of the hole relaxation is probably associated with their slower velocity in the matrix/wetting layer. Using the


xxi

Proc. of SPIE Vol. 8553 855301-21


6

5

4

3

2

1

020 40 60 80 100

Temperature, °C

120 140

extracted value of h we can also reproduce fairly well temperature dependences of the two-state lasing threshold and the current of the GS-lasing quenching.

Using the proposed model we are capable of calculating the operation diagram of QD laser as shown in Figure 2,b. The diagram depicts different regimes of the laser operation as a function of electron (geC) and hole (ghC) capture rates: subthreshold regime of no lasing (NL), regime of lasing via GS optical transition (GS), two-state lasing regime (GS+ES1), regime of lasing via ES1 transition only (ES1). Depending on the ratio of hole-to-electron relaxation rates (h = ghC/geC) and the total optical loss various scenarios of laser behavior can be realized. In particular, in case of sufficiently fast hole capture (h = 1 in Figure 2,b) the two-state lasing can persist so that the GS lasing peak is not completely suppressed even at very high injection levels.

2.3 Effect of p-type doping

Modulation p-type doping of QDs may noticeably improve temperature stability of the threshold current12. We found that p-doping affects the two-state lasing behavior as well. Temperature dependences of the two-state lasing threshold current as well as the ground-state lasing threshold current are presented in Figure 3 for two 0.6-mm-long diodes of similar design (10 planes of InAs/InGaAs QDs): one with undoped active region and another with modulation doping (~10 acceptors per QD). The GS-lasing thresholds measured at room temperature are nearly equal in both structures (~0.35 A). At the same time, the onset of the two-state lasing is significantly shifted to higher currents in the p-type doped laser (~5.5 A) as compared to its undoped analogue (~1.1 A). Light-current curve (insert of Figure 3) demonstrates that the maximum optical power of the GS spectral component reaches 3.6 W in the laser with p-type doping, while it is about 2.4 W in the undoped counterpart. Another finding is that the temperature interval, where GS lasing can be achieved, extends to higher temperatures in the p-doped structure (from 55 to 100oC).

Figure 3. Threshold vs temperature for ground-state lasing (solid symbols) and two-state lasing (open symbols) in lasers with undoped (circles) and p-type doped (squares) QDs. Insert: power of the GS-line vs current.

2.4 Comparison of lasing and spontaneous emission spectra

Spontaneous emission spectra may provide additional information on peculiarities of the two-state lasing. We studied QD lasers having 4 cleaved facets where both lasing and spontaneous emission can be simultaneously detected as shown in Figure 4. At least five peaks of different origin are easily resolved: two narrow peaks of lasing emission via ground-state (1264.3 nm) and first excited-state (1179.8 nm) transitions and three broad peaks of spontaneous emission via ground-state (1264.0 nm), first excited (1172.0 nm) and second excited-state (1108.4 nm) transitions. The characteristic feature is that the GS lasing peak nearly coincides with the peak position of GS spontaneous emission. This implies that the GS lasing arises from QDs of the most probable (mean) size. At the same time ES1 lasing peak is noticeably red-shifted with respect to the peak position of ES1 spontaneous emission indicating that QDs, which size is larger than the mean one, are chiefly responsible for the ES lasing. Similar behavior was observed in a wide interval of current density.


xxii

Proc. of SPIE Vol. 8553 855301-22


100

60

40

ti 20

E 0

000

Lasing

0

GS

0

ES1

o

0

ES1

GS

200 500 1000 1500 2000 2500Current density, A/cm'

1000

ES2

. experimentfit: lasing

- fit: spont. rr

1100 1200

Wavelength, nm

1300

f

D

GaAs with1QDT (AIGa)XOy

Figure 4. Emission spectrum: squares – experiment, solid curves – lasing emission, dotted curves – spontaneous emission. Insert: peak position vs current density: solid circles – GS lasing, open circles – ES1 lasing, solid curve – GS spontaneous emission, dotted curve – ES1 spontaneous emission.

3. MICRORING STRUCTURES 3.1 Experiment

An epitaxial structure was grown by molecular beam epitaxy on semi-insulating GaAs(100) substrate. An active region comprises five layers of InAs/In0.15Ga0.85As QDs separated by 30-nm-thick GaAs spacers. The active region was inserted into a 220-nm-thick GaAs waveguiding layer confined by 20-nm-thick Al0.3Ga0.7As barriers. A 400-nm-thick Al0.98Ga0.02As cladding layer was grown beneath the waveguiding layer. Microrings were defined by photolithography and Ar+-etching. The outer diameter was varied in different structures from D = 4 to 9 μm. The inner diameter ranges from d = 0 (microdisks) to d ≈ 0.8D. Finally, the cladding layer was selectively oxidized into (AlGa)xOy. Typical microphotograph of the resonator structure is shown in Figure 5.

Figure 5. SEM image of QD microring laser (D =6 μm, d = 2 μm).

For optical experiments a CW-operating YAG:Nd laser (λ = 532nm) was used together with a cooled Ge pin-diode. Measurements at elevated temperatures were performed with the structures mounted onto a heated holder equipped with a temperature controller. Low temperature measurements were done in a flow cryostat.


xxiii

Proc. of SPIE Vol. 8553 855301-23


10°

101

to 2.

1031140

(35,3);(39,2)

(32,4)

(34,3);

(38,2);(43,1)

(31,4)

'(37,2);(33,3)1

(42,1)(30,4)

(32,3)

(36,2)

(29,4)

(44,1)(41,1)

1160 1180 1200 1220

Wavelength, nm

1240 1260

3.2 Low-temperature measurements

An example of luminescence spectrum taken at 77 K from 6µm-ring with 2µm inner diameter is shown in Figure 6. Four series of whispering gallery modes of different radial order are clearly observed. All modes presented in the optical spectrum were identified by means of 2D‐axisymmetric analysis. The dominant modes are of n = 2 and 3 order. Significant overlap of many modes exists (e.g. around 1190.8 nm where 3 modes are close together).

Figure 6. Low-temperature luminescence spectrum of the microring. Estimated mode orders TEm,n are indicated near the peaks.

3.3 Near-field scanning optical microscopy.

Spatial distribution of light intensity inside the microresonators was studied by means of near-field scanning optical microscopy (NSOM). Several typical NSOM images are presented in Figure 7. Characteristic WGM patterns are clearly seen. Depending on spectral position of the luminescence peaks, NSOM images reveal modes of different radial and azimuthal order.

λ = 1279.8 nm, TE1,32 λ = 1291.3 nm, TE2,29

Figure 7. NSOM images demonstrating WGM modes of different orders in the microring resonator.

3.4 Room-temperature measurements.

A representative room-temperature µ-PL spectrum taken under low excitation is shown in the left insert of Figure 8. Full width at half maximum for resonant peaks varies from 0.143 to 0.234 nm giving the quality factor of about 9000.

The threshold power for the microring/microdisk structures was estimated from a light-light curve of the dominant mode. An example is presented in Figure 8 where a characteristic knee is clearly seen. In this particular case (D = 7 µm,


xxiv

Proc. of SPIE Vol. 8553 855301-24


Excitation power, mW

03

2

1

ó0

Inner diameter d, µm2 4 6

1.0

E 0.8tiô0.6

0.4

0.2

0.04 6 8 10Outer diameter D, gm

D=7µm

0.2 0.4 0.6 0.8

Relative inner diameter dID10

d = 3.4 µm) the threshold power is 0.37 mW. No correction was made to take into account partial light reflection from the surface or waste of the excitation power in the inner area of microring structures. Overall the threshold power at room temperature in different structures ranges from few tenths of mW to few mW. From one to three modes were usually observed in room-temperature lasing spectra (see right insert of Figure 8).

Figure 8. Intensity of the dominant mode against excitation power (symbols). Curve is a guide to the eye. Insert: luminescence spectrum below threshold (left) and above threshold (right).

Room-temperature threshold characteristics of the microstructures with different inner diameters were compared. In most cases the threshold power (absolute value) decreases by approximately 30-40% as the inner diameter increases from 0 (disk) to 0.3-0.6 D, see Figure 9. Further ring thinning results in rapid growth of the threshold. As for the effect of the outer diameter, the lowest threshold of 0.37-0.4 mW was found in microrings having an outer diameter of 6–7 µm. Both larger and smaller microrings demonstrate higher threshold power as shown in the insert of Figure 9.

Figure 9. Room-temperature threshold (normalized to the threshold of the microdisk structure) as a function of inner diameter. Insert: the lowest threshold against the outer diameter.

3.5 High-temperature measurements

Threshold power increases super-exponentially with temperature. Around room temperature the characteristic temperature was estimated to be ~60–75 K. In most cases, lasing can be observed up to 80–90oC whereas the highest temperature of lasing was found to be as high as 107oC, Figure 10. To the best of our knowledge this is the highest


xxv

Proc. of SPIE Vol. 8553 855301-25


5

4-

D E E D

1

020 40

1.40

60 80

Temperature, °C

1001.25

120

temperature ever reported for 1.3μm QD MRLs. Below room temperature the threshold is nearly unchanged or even slightly increases. Temperature variation of the lasing wavelength is summarized in Figure 10. Spectral position of the ground-state optical transition of quantum-dot luminescence is also shown for comparison. It is seen that the lasing wavelength is quite stable (~0.05 nm/K) within relatively wide temperature intervals (e.g. from 20 to 40oC and then from 50 to 90oC) where a certain WGM mode remains the dominant one. Abrupt changes of the lasing wavelength (e.g. around 40-50 oC) are due to hopping of the dominant mode.

Figure 10. Temperature dependences of the threshold power (solid symbols) and wavelengths of the dominant mode (open symbols). QD ground-state optical transition against temperature (dashed curve) is also shown. Solid curve is exponential fit with T0=65 K.

4. CONCLUSIONS Quantum dot lasing structures of two sorts both emitting around 1.3 µm were studied: broad-area diode lasers and optically pumped microresonators.

Broad-area lasers were used for detailed investigation of the two-state lasing phenomenon and, in particular, quenching of the ground-state lasing emission that observed at high currents. It was demonstrated that the most probable reason for the GS lasing quenching is asymmetry of electrons and holes carrier distributions. Additionally, difference in capture rates of electrons and holes has to be taken into consideration. We also found that the GS-component reaches its maximum beyond the threshold of the two-state lasing and that different groups of QDs are responsible for GS- and ES1-lasing in the two-state lasing regime. Finally, we demonstrated that p-type modulation doping of QDs leads to noticeable suppression of the ES1-lasing thereby resulting in enhancement of peak power of the GS spectral component.

Microrings and microdisks of few micrometers in diameter were made by ion etching and selective oxidation with Q-factor of about 9000. Whispering gallery modes of second and third radial orders dominate the luminescence spectrum. Nearly single-mode lasing was observed at elevated temperatures. The lowest threshold (around 0.4 mW at RT) was found in microdisks of intermediate diameter (6-7 µm) with approximately 50% inner aperture. The highest temperature was found to be 107oC and the threshold was in mW-range.

ACKNOWLEDGEMENTS

The work is supported in different parts by Russian Ministry of Science and Education, Russian Foundation for Basic Research, Programs of Fundamental Studies of the Russian Academy of Sciences. NVK is thankful for support to Saint-Petersburg`s Committee on Science and Higher School.


xxvi

Proc. of SPIE Vol. 8553 855301-26


REFERENCES

[1] Zhukov, A. E., Kovsh, A. R., Livshits, D. A., Ustinov, V. M. and Alferov, Zh. I., “Output power and its limitation in ridge-waveguide 1.3 µm wavelength quantum-dot lasers,” Semicond. Sci. Technol. 18(8), 774-781 (2003).

[2] Markus, A., Chen, J. X., Gauthier-Lafaye, O., Provost, J.-G., Paranthoën, C. and Fiore, A., “Impact of intraband relaxation on the performance of a quantum-dot laser,” IEEE J. Select. Topics Quantum Electron. 9(5), 1308-1314 (2003).

[3] Markus, A. and Fiore, A., “Modeling carrier dynamics in quantum-dot lasers,” phys. stat. sol. (a) 201(2), 338–344 (2004).

[4] Ji, H.-M., Yang, T., Cao, Y.-L., Xu, P.-F., Gu, Y.-X. and Wang, Zh.-G., “Self-heating effect on the two-state lasing behaviors in 1.3-μm InAs–GaAs quantum-dot lasers,” Jpn. J. Appl. Phys. 49(7), 072103 (2010).

[5] Sugawara, M., Hatori, N., Ebe, H., Ishida, M., Arakawa, Y., Akiyama, T., Otsubo, K. and Nakata, Y., “Modeling room-temperature lasing spectra of 1.3-µm self-assembled InAs/GaAs quantum-dot lasers: Homogeneous broadening of optical gain under current injection,” J. Appl. Phys. 97(4), 043523 (2005).

[6] Liang, D., Fiorentino, M., Srinivasan, S., Bowers, J. E. and Beausoleil, R. G., “Low threshold electrically-pumped hybrid silicon microring laser,” IEEE J. Selected Topics Quantum Electron., 17(6), 1528 - 1533 (2011).

[7] Ouyang, D., Ledentsov, N. N., Bimberg, D., Kovsh, A. R., Zhukov, A. E., Mikhrin S. S. and Ustinov, V. M., “High performance narrow stripe quantum-dot lasers with etched waveguide,” Semicond. Sci. Technol. 18(12) L53-L54 (2003).

[8] Cao, H., Xu, J. Y., Xiang, W. H., Ma, Y., Chang, S.-H., Ho, S. T. and Solomon, G. S., “Optically pumped InAs quantum dot microdisk lasers,” Appl. Phys. Lett. 76(24), 3519-3521 (2000).

[9] Ide, T., Baba, T., Tatebayashi, J., Iwamoto, S., Nakaoka, T. and Arakawa, Y., “Room temperature continuous wave lasing in InAs quantum-dot microdisks with air cladding,” Opt. Express 13(5), 1615-1620 (2005).

[10] Munsch, M., Claudon, J., Malik, N. S., Gilbert, K., Grosse, P., Gerard, J.-M., Albert, F., Langer, F., Schlereth, T., Pieczarka, M. M., Hofling, S., Kamp, M., Forchel, A. and Reitzenstein, S., “Room temperature, continuous wave lasing in microcylinder and microring quantum dot laser diodes,” Appl. Phys. Lett. 100(3), 031111 (2012).

[11] Viktorov, E. A., Mandel, P., Tanguy, Y., Houlihan, J. and Huyet, G., “Electron-hole asymmetry and two-state lasing in quantum dot lasers,” Appl. Phys. Lett. 87(5), 053113 (2005).

[12] Fathpour, S., Mi, Z., Bhattacharya, P., Kovsh, A. R., Mikhrin, S. S., Krestnikov, I. L., Kozhukhov, A. V., and Ledentsov, N. N., “The role of Auger recombination in the temperature-dependent output characteristics (T0=∞) of p-doped 1.3 µm quantum dot lasers,” Appl. Phys. Lett. 85(2), 5164-5166 (2004).


xxvii

Proc. of SPIE Vol. 8553 855301-27


Proc. of SPIE Vol. 8553 855301-28


Documents

Macquarie University ResearchOnline...Fluorescence microscopy has become an essential tool to study biological molecules, pathways and events in living cells, tissues and animals