Non-linear optics

Laboratoire Temps – Fréquence (LTF)

Thomas Südmeyer Time/Frequency Laboratory, Physics Institute, University of Neuchatel Les Houches, 23.04.2015

Ultrafast OPOs and OPGs. Novel high power sources and their challenges

Laboratoire Temps – Fréquence (LTF) 23.04.2015


The Time/Frequency Laboratory at the University of Neuchâtel






2015 Les Houches NLO School






Overview

Ultrafast lasers Ultrafast high power lasers Nonlinear temporal pulse compression Nonlinear high power frequency conversion: an RGB system for laser projection Nonlinear UV generation Nonlinear VUV/XUV generation


What is ULTRAFAST?


Resolving fast events

Cinema: time between images 124 Hz

= 42 ms


The horse in motion

Baronet, 1794

www.wikipedia.org

George Stubbs (1724-1806): English painter, best known for his paintings of horses.

Whistlejacket, 1762

http://www.wikipedia.org/


Fast mechanical shutter photography E. Muybridge in 1878: understand horse gallop using fast photography in the ms-domain


Fast flash photography Harold E. Edgerton (1903-1990): understand fast processes using flash light (limited by duration of flashes to µs-domain)








Femtochemistry by A. H. Zewail in 1994 A. H. Zewail in 1994: understand transition states in chemical reactions using fs-pulses


Scales

picosecond 10–12 s

femtosecond 10–15 s

nanosecond 10–9 s

Time


Ultrafast laser pulses

Observe and use fast dynamics • understand chemical reaction dynamics • fast communication • …

Access ultrashort time scales

interconnects optical clocking





Concentrate in time and space Achieve extremely high intensities • material processing, eye surgery, … • biomedical imaging, …. • high field science, …

40x





Concentrate in time and space

Broad optical spectrum

Achieve extremely high intensities • material processing, eye surgery, … • biomedical imaging, …. • high field science, …

Generate ultrastable frequency combs • high precision spectroscopy • optical clocks • …


Key advantage of laser light: coherence

Spatial coherence Propagation over long distances & reduced divergence…

… or extremely small spot & high divergence


Key advantage of laser light: coherence

Long duration and very small spectrum …

… or short pulses and wide spectrum

⇒ Ultrafast lasers and frequency combs!

Spatial coherence Temporal coherence Propagation over long distances & reduced divergence…

… or extremely small spot & high divergence


Continuous-wave laser

Light circulates in resonator

Losses compensated by gain in laser medium (which is externally pumped)

Gain saturates to a level that it compensates the losses

Light emission typically continuous


Passively modelocked laser

Short pulse circulates in cavity (fs-ps)

High repetition rate pulse train at the output (MHz-GHz)

Pulse formation process initiated and stabilized by saturable absorber in the laser cavity

Steady-state pulse parameters: governed by interplay of gain, (saturable) loss, dispersion, Kerr nonlinearity, etc.

Saturable loss


Modelocking and frequency combs

http://www.physik.uni-wuerzburg.de/femto-welt/pulsframe.html

http://www.physik.uni-wuerzburg.de/femto-welt/pulsframe.html


A 5 fs pulse

λ/c = 2.7 fs @800 nm


A 5 fs pulse

speed of light

5 fs ⋅ 𝑐𝑐 = 1.5 µ𝑚𝑚


SESAM (Semiconductor Saturable Absorber Mirror)

Animation: http://www.rp-photonics.com/mode_locking.html

http://www.rp-photonics.com/mode_locking.html



DBR mirror semiconductor saturable absorber

• Semiconductor absorber

• Integration in mirror structure

U. Keller, et al., IEEE J. Sel. Top. Quant. 2, 435 (1996)



• Key parameters – saturation fluence Fsat – modulation depth ∆R – nonsaturable losses ∆Rns

– roll-over F2 – recovery time τ

DBR mirror semiconductor saturable absorber

• Semiconductor absorber – typically QW or QD layer(s) – number of layers – growth temperature – material composition, …

• Integration in mirror structure – field strength in absorber – dispersion – reflectivity, OC, …

U. Keller, et al., IEEE J. Sel. Top. Quant. 2, 435 (1996)


Key parameters: pulse energy

repetition rate average power ( = Ep frep) pulse duration

peak power ( ∝EP / τP )

Ep

frep Pave

τp Ppeak

… generate coherent light pulses with pico- or femtosecond duration

frep : pulse repetition rate frequency

fCEO : carrier envelope offset frequency

fn = fCEO + nfrep

Frequency comb: frequency domain

time domain TR = 1 / frep

τp



Overview



Industry: High-precision, high-speed micromachining Required • High EP > 10 µJ • High Ppk > 10 MW Wanted • High frep (MHz) Liu, et al., Proc. SPIE,

Vol. 5713, 2005

T. Südmeyer, et al., Nat. Phot. 2, 599 (2008)

Fuel injection nozzles Stents Inkjet nozzles

Nolte, et al., Adv. Eng. Mater. 2, 2000

Profeta et al., Industrial Laser Solutions, 2004

Science: Strong-field physics applications

HHG Spectroscopy T. Auguste, et al.,

PRA 80, 033817 (2009)

Required • High Ipeak > 1014 W/cm2

• Short pulses p < 100 fs Wanted • High frep (MHz)

High average power Pav = Epˑ frep

Attosecond science

A. Pfeiffer et al., Nat. Phys. 8, 76 (2012)

High average power Pav = Epˑ frep

Applications for high power sources


Frontier: average power and pulse energy

High energy and MHz

T. Südmeyer, et al., “Femtosecond laser oscillators for high-field science”, Nature Photonics 2, 559 (2008)

Industrial applications • increase throughput, • reduce costs per item, …

Scientific applications

• reduce measurement time, • increase signal-to-noise, • MHz XUV sources, …

Nolte, et al., Adv. Eng. Mater. 2, 2000


• Operation at reduced peak intensity

• Reduced interaction volume

Chirped pulse amplification (CPA) : 830 W, 640 fs Innoslab : 1.1 kW, 615 fs P. Russbueldt, et al., Opt. Letters 35, 4169-4171 (2010) T. Eidam, et al., Optics Letters 35, 94-96 (2010)

Fiber Slab Thin disk

Key for high average power: heat removal

• Optimization of surface-to-volume ratio for efficient cooling

Key for ultrafast: reduce nonlinearities

High average power ultrafast sources


• Operation at reduced peak intensity

• Reduced interaction volume

Chirped pulse amplification (CPA) : 830 W, 640 fs Innoslab : 1.1 kW, 615 fs P. Russbueldt, et al., Opt. Letters 35, 4169-4171 (2010) T. Eidam, et al., Optics Letters 35, 94-96 (2010)

Fiber Slab Thin disk

Key for high average power: heat removal

• Optimization of surface-to-volume ratio for efficient cooling

Key for ultrafast: reduce nonlinearities

High average power ultrafast sources


Highest average powers and highest energies of any ultrafast oscillator technology

Ep = 80 μJ

τp = 1.07 ps frep = 3 MHz Pav = 242 W

Ep = 17 µJ Pav = 275 W τp = 583 fs frep = 16.3 MHz

C.J. Saraceno, et al., Optics Express 20, 23535 (2012)

SESAM Modelocked Thin Disk Lasers


Challenges for high power operation

• Pulse formation – sustain high intracavity intensities – avoid mode locking instabilities

saturable reduced losses for absorber pulsed operation

cw mode locking

EP = Pavg ∙ TR

QML

Challenges • TEM00 operation at high average power

– efficient heat removal – suitable cavity design – suitable broadband gain material

QML cw mode locking QML


Challenge: Fundamental mode operation despite high thermal load - Suitable gain material (good optical quality, high thermal conductivity)

- Suitable gain geometry (efficient heat removal)

Thin disk laser A. Giesen, et al., Appl. Phys. B 58, 365 (1994)

- Efficient heat removal through back side

- Power scalable by increase of mode diameter D (constant intensities)

- 1D longitudinal heat flow → reduced thermal lensing

Thin disk laser


Multi-pass pumping scheme for efficient absorption

Pump module - Typical single-pass absorption 8% - 15% - Pump module with up to 32 passes available (here 24 passes) - Typical over 98% of absorbed pump light - Homogeneous pump light distribution - Low demand on pump brightness (pump diameters of mm-cm)

pump fiber disk

parabolic mirror

Front view

Thin disk laser


Modelocked thin disk laser

Animation by Martin Hoffmann


• efficient heat removal: → material properties: thermo-mechanical

and spectroscopic properties → disk quality: thickness, diameter → contacting

• suitable cavity design

Challenge 1: TEM00 operation at high average power

Yb:YAG: the standard thin disk material • large disks on diamond with excellent quality

commercially available • 500 W fundamental transverse mode

(M2<1.1) demonstrated#1

• 1.1 kW nearly fundamental mode (M2<1.5) #2

#1 A.Killi, et al., Proceedings of the SPIE, Volume 7193, 2009 #2 Peng, et. al., Opt. Lett 38, 10, pp. 1709-1711, 2013

< 100 µm thick

glued on water cooled diamond

High-power modelocking: challenges

C. R. E. Baer, et al., Optics Express 20, 7054-7065 (2012)


• efficient heat removal: → material properties: thermo-mechanical

and spectroscopic properties → disk quality: thickness, diameter → contacting

• suitable cavity design C. R. E. Baer, et al., Optics Express 20, 7054-7065 (2012)

Challenge 1: TEM00 operation at high average power


Many other promising materials currently being investigated!

• Yb: CALGO • >70% slope efficiency • 62 fs pulses

• Yb doped sesquioxides • Etc…


Challenge 2: Pulse formation at high intracavity peak power

➝ Soliton modelocking: balance self-phase modulation and negative dispersion ➝ Thin-disk geometry: excellent for low nonlinearities ➝ Avoid modelocking instabilities from excessive nonlinearities at very high intracavity

levels ➝ Origin of nonlinearities: mostly air in resonator

F. X. Kartner and U. Keller, Opt. Lett. 20(1), 16–18 (1995) R. Paschotta and U. Keller, Appl. Phys. B 73(7), 653–662 (2001)

Avoid excessive nonlinearities!



Helium flooding 45 W, 11 µJ, 790 fs

Harnessing intracavity nonlinearities

n2,air ≈ 3.10-23 m2/W n2,He ≈ 8.10-26 m2/W (≈ 400 times lower)

S. Marchese, et al., Optics Express 16, 6397-6409 (2008)


Helium flooding 45 W, 11 µJ, 790 fs Multiple passes 145 W, 41 µJ, 1.1 ps


number of passes gain per roundtrip

efficient laser operation at lower OC rate for a given output power: reduced nonlinearities

D. Bauer, et al., Optics Express 20, 9698-9704 (2012)


minimum nonlinearity: higher intracavity peak power can be tolerated

easy adjustment of SPM by adjusting pressure minimum pointing instabilities, cleanliness

Helium flooding 45 W, 11 µJ, 790 fs Multiple passes 145 W, 41 µJ, 1.1 ps Vacuum 275 W, 17 µJ, 580 fs Vacuum 240 W, 80 µJ, 1.07 ps

C.J. Saraceno, et al., Optics Express 20, 23535 (2012)



First design (275 W modelocked laser): • 17 MHz cavity with one double-pass through the disk • OC rate used for modelocking experiments: 11% • Problems with thermal effects in dispersive mirrors

EP = Pavg ∙ TR Increase cavity length to increase pulse energy!

Energy scaling


New cavity: Two double-passes through the disk: higher gain, efficient operation with higher Toc reduced intracavity power for lower thermal effects

Energy scaling


New cavity: Two double-passes through the disk Beam shaping Thin-film polarizer for polarization selection

frep = 5.8 MHz Toc = 25 %

Energy scaling


D = n ∙ d = 23.4 m

MPC-length

Cavity extension with Heriott-type Multi-Pass Cavity (MPC):

D. Herriott, et al., Appl. Opt. 3, 523 (1964)

Energy scaling


New cavity: Two double-passes through the disk Thin-film polarizer for polarization selection Herriott-type multipass cell (10 m mirror)

frep = 3 MHz Toc = 25 % 300 W single

fundamental mode

Energy scaling


Soliton modelocking: Self-phase modulation (remaining

atmosphere at ≈1 mbar) 390 µrad/MW

Negative dispersion (GTI-type mirrors)

GDD = -28000 fs2 per roundtrip

Energy scaling


SESAM with multiple QW and dielectric topcoating for high damage threshold#1

- Fsat = 120 μJ/cm2

- ΔR = 1.1 % - ΔRns = 0.1 % #1 C.J. Saraceno, et al., IEEE JSTQE, vol 18, no.1, pp 29-41 (2012)

Energy scaling


➝ Highest pulse energy from any ultrafast oscillator

Pavg = 242 W τp = 1070 fs

Ppump = 790 W ηopt = 30 % frep = 3.03 MHz M2 < 1.05 EP = 80 µJ τP∙Δν = 0.39 Ppk = 66 MW (ideal: 0.315)

Results

C. Saraceno, F. Emaury, C. Schriber, M. Hoffmann, M. Golling, T. Südmeyer, U. Keller, Optics Letters, 39, 9 (2014)


Overview



First pulse compression of an ultrafast TDL (2003)







Calculated propagation in the fiber

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 time (ps)

wavelength (nm) 980 1030 1080

pow

er (a

.u)

spec

tral

inte

nsity

phase

Time domain

Frequency domain



Calculated propagation in the fiber

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 time (ps)

wavelength (nm) 980 1030 1080

pow

er (a

.u)

spec

tral

inte

nsity

phase

Time domain

Frequency domain





T. Südmeyer, F. Brunner, E. Innerhofer, R. Paschotta, K. Furusawa, J. C. Baggett, T. M. Monro, D. J. Richardson, and U. Keller, "Nonlinear femtosecond pulse compression at high average power levels by use of a large-mode-area holey fiber," Opt. Lett. , vol. 28, 1951-1953 (2003).




Yb:YAG Yb:YAG

Pav 275 W 242 W

τp 583 fs 1.07 ps

Ep 17 µJ 80 µJ

Pp 25 MW 66 MW

For most targeted scientific applications

→ Shorter pulses < 100 fs are required

Compression in gas-filled HC-PCF

Compression of few µJ level pulses to sub-50 fs at 4 MHz F. Emaury et al, Optics Express 21, 4986 (2013)

Compression/transmission of mJ level pulses at 1 kHz C. Fourcade Dutin et al, Postdeadline Paper CTh5C.7 CLEO US 2013

Compression of 40 µJ level pulses at 3 MHz (100 W)

Pulse compression today


Available at fiber launch: Pav = 150 W Ep = 50 µJ frep = 3 MHz τp = 1.1 ps

Pulse compression

Florian Emaury, Clara J. Saraceno, Benoit Debord, Debashri Ghosh, Andreas Diebold, Frederic Gerome, Thomas Südmeyer, Fetah Benabid, and Ursula Keller, “Efficient Pulse Compression in the 100-W Average Power Regime Using Gas-Filled Kagome Hollow-Core Photonic Crystal Fibers” Optics Letters Vol. 39, Issue 24, pp. 6843–6846 (2014)


Fiber: • Kagome-type HC-PCF 7-

cell hypocycloid core • MFD ≈ 30 µm • Ar-filled: 5 bar • Length = 67 cm

Transmission 92% at maximum power 134 W out for 144 W launched: highest value through Kagome

Pulse compression

Available at fiber launch: Pav = 150 W Ep = 50 µJ frep = 3 MHz τp = 1.1 ps


Compression with 80% total power efficiency Output: 100 W compressed to sub-200 fs

Expected soon: sub-50 fs, better compression efficiency with chirped mirrors

123 W 41 µJ 1.2 ps

Pulse compression


Overview



F. Brunner, E. Innerhofer, S. V. Marchese, T. Südmeyer, R. Paschotta, T. Usami, H. Ito, S. Kurimura, K. Kitamura, G. Arisholm, and U. Keller, “Powerful red-green-blue laser source pumped with a mode-locked thin disk laser,” Opt. Lett. 29, 1921-1923 (2004).

• Pump source: ultrafast thin disk laser

1030 nm

thin disk laser

Efficient RGB system pumped by a TDL (1.4 µJ, 780 fs)



• Pump source: ultrafast thin disk laser • RGB setup

• second-harmonic generation (SHG)

515 nm 1030 nm

thin disk laser SHG

1030 nm





• second-harmonic generation (SHG) • two-stage OPG

• optical parametric generation (OPG) • optical parametric amplification (OPA)

RGB

515 nm 1030 nm 799 nm

thin disk laser

two-stage OPG SHG

515 nm 1030 nm

1450 nm







• two sum frequency mixers (SFM)

RGB

515 nm 1030 nm 799 nm 1450 nm

450 nm

thin disk laser

two-stage OPG SHG SFM

red

603 nm 515 nm

SFM blue

1030 nm

1450 nm







• two sum frequency mixers (SFM)

RGB

515 nm 1030 nm 799 nm 1450 nm

450 nm

thin disk laser

two-stage OPG SHG SFM

red

603 nm 515 nm

SFM blue

1030 nm

1450 nm



Pavg = 79 W Ep = 1.39 µJ τp = 780 fs Ppeak = 1.57 MW frep = 56.8 MHz τp ∆ν = 0.37 M 2 < 1.2 linearly polarized

autocorrelation optical spectrum

Time delay (ps)

τp = 780 fs

Wavelength (nm)

1.67 nm

Pump source: modelocked TDL


mode-locked thin disk laser

SHG in LBO

79 W

1030 nm

515 nm

up to 48 W at 515 nm (66% conversion efficiency)

pump power @ 1030 nm (W)

SHG

pow

er (W

) w1030 = 150 µm

• 5-mm long LBO crystal • critically phase-matched • at room temperature

Second Harmonic Generation


Generation of blue and red color by sum frequency mixing of

1030 nm + 799 nm 450 nm 1030 nm + 1450 nm 603 nm

requires multi-watt power at 799 nm and 1450 nm

How to get red and blue?


• optical parametric oscillator (OPO) • active stabilization of cavity length required

#) T. Südmeyer et al., Opt. Lett. 26, 304 (2001)

• fiber-feedback optical parametric oscillator #)

• feedback through a single mode fiber • no active stabilization required

• optical parametric generator (OPG) • only few optical components • OPG at high repetition rates

• femtosecond pulses with up to 2.5 W *)

• picosecond pulses with up to 9.5 W †)

*) T. Südmeyer et al., CLEO (2002), Talk CTuO4 †) B. Köhler et al., Appl. Phys. B 75, 31 (2002)

Flexible wavelength conversion


Gain guiding in high-gain parametric devices:

nonlinear crystal

• highest conversion takes place at crystal end • gain guiding reduces signal radius:

signal radius << pump radius in power amplifier section

G. Arisholm, R. Paschotta, T. Südmeyer, JOSA B 21 (3), 578 (2004)

preamplifier section power amplifier section

pump signal

Challenges for efficient high power OPG


Pump depletion causes „hole” in pump profile

Consequence: trade-off between conversion efficiency and beam quality in high-gain processes

Conversion efficiency

M2 fa

ctor

of s

igna

l

Position (mm)

Nor

m. F

luen

ce pump in

pump out

low gain situation

pump in pump out

Position (mm)

Nor

m. F

luen

ce

high gain situation



reliable operation with multi-watt power at 799 nm and 1450 nm and good beam quality

Solution: two-stage approach: • first stage: OPG with limited pump depletion

(Note: conversion efficiency not important) • second stage: OPA with good conversion efficiency,

but limited gain ( weak gain guiding)

first stage : OPG second stage: OPA

• seed wave generated • limited pump depletion

• optimized mode areas • limited gain

1030 nm 1450 nm 799 nm

1450 nm

PPSLT LBO

515 nm




SHG in LBO

1030 nm

1030 nm

λ/2

1450 nm

OPG in PPSLT

79 W

1030 nm

515 nm OPG in PPSLT 8W@1030 nm ⇒ 1.6W@1450 nm + 3556 nm

double-pass in uncoated 17.5-mm PPSLT (150 °C, 29 µm period)

OPG in PPSLT



SHG in LBO

OPA in LBO

799 nm

1030 nm

1030 nm

1450 nm λ/2

515 nm 1450 nm

OPG in PPSLT

23 W 515-nm

79 W

42 W

1030 nm

515 nm

OPA 515 nm + 1450 nm

• amplification of 1450 nm, generation of 799 nm • 10-mm long LBO crystal • critically phase-matched (20°C)

1.6 W

1450 nm: 7 W, 1.2 ps 799 nm: 12 W, 0.7 ps

OPA in LBO



SHG in LBO

OPA in LBO

SFM in LBO

1030 nm

799 nm

1030 nm

1030 nm

1450 nm λ/2

515 nm 1450 nm

OPG in PPSLT

450-nm

515-nm

79 W

42 W

23 W 1030 nm

515 nm

Sum frequency mixing

23 W


603-nm mode-locked thin disk laser

SHG in LBO

OPA in LBO

SFM in LBO

1030 nm

799 nm

1030 nm

1030 nm

1450 nm λ/2

515 nm 1450 nm

OPG in PPSLT

450-nm

515-nm

79 W

SFM in LBO

42 W

23 W 1030 nm

515 nm


23 W


• 15-mm long LBO crystal • nearly non-critically phase-matched at room temperature

SFM: 1030 nm + 1450 nm 603 nm

Spe

ctra

l Int

ensi

ty (a

.u.)

1.1 nm

Wavelength (nm)

603-nm output: Pavg = 8 W M 2 = 1.1

• 10-mm long LBO crystal • critically phase-matched at room temperature

SFM: 1030 nm + 799 nm 450 nm

0.6 nm

Spe

ctra

l Int

ensi

ty (a

.u.)

Wavelength (nm)

450-nm output: Pavg = 10.1 W

M 2 = 1.1



603-nm 8 W mode-locked

thin disk laser

SHG in LBO

OPA in LBO

SFM in LBO

1030 nm

799 nm

1030 nm

1030 nm

1450 nm λ/2

515 nm 1450 nm

OPG in PPSLT

450-nm 10.1 W

515-nm

79 W

SFM in LBO

42 W

23 W 1030 nm

515 nm

Experimental setup

23 W


µJ pulses with ∼1 ps are well-suited for efficient RGB generation

• OPG-based: no synchronized cavities • Simple system design • Optimal operation Yb-YAG TDLs

Latest generation TDL with 275 W ⇒ expect >30 W per color

RGB output Pavg @ 603 nm = 8.0 W Pavg @ 515 nm = 23.0 W Pavg @ 450 nm = 10.1 W pulse durations ≈ 1 ps

Ultrafast thin disk laser DPSSL Pavg @ 1030 = 80 W repetition rate = 57 MHz

RGB output


http://www.sony.net/Products/SC-HP/cx_news/vol40/pdf/sideview40.pdf

BUT: never used for projection… However, other lasers did

(Sony Annual Report 20015)



Sony Laser Dream Theater at the Aichi Expo 2005














Green laser: optically-pumped VECSEL (OSRAM) Ulrich Steegmueller et al., “Progress in ultra-compact green frequency doubled optically pumped surface emitting lasers”, High-Power Diode Laser Technology and Applications VII, Proc. of SPIE Vol. 7198 719807, 2009 H. Lindberg et al., “Recent advances in VECSELs for laser projection applications”, Vertical External Cavity Surface Emitting Lasers (VECSELs), Proc. of SPIE Vol. 7919 79190D, 2011

less than 0.4cm3 >70 mW green

Microvision laser projector


Overview



Nonlinear UV generation

• >20 W green • 88% external efficiency • M²=1.00x1.03

T. Südmeyer, Y. Imai, H. Masuda, N. Eguchi, M. Saito, and S. Kubota, “Efficient 2nd and 4th harmonic generation of a single-frequency, continuous-wave fiber amplifier”, Opt. Express, 1546 (2008)












Overview



Optics and Photonics News, Vol. 19, Issue 10, pp. 24-29 (2008) http://dx.doi.org/10.1364/OPN.19.10.000024

⇒ until 2000: limited to fs regime Pulses generated directly out of laser oscillators operating in VIS/IR spectral region.

Pulse duration of ultrafast sources


Optics and Photonics News, Vol. 19, Issue 10, pp. 24-29 (2008) http://dx.doi.org/10.1364/OPN.19.10.000024

Attosecond pulses High harmonic generation of intense fs-pulses results in as-pulses in VUV/XUV spectral regime

Pulse duration of ultrafast sources


infrared fs-pulses

XUV

light intensity 1013-1015 W⋅cm-2

gas target

IR beam block

E.A. Gibson, Science 302, 98 (2003)

Extreme nonlinear up-conversion of IR fs-pulses in gas target • broad range of coherent UV-XUV radiation • attosecond duration

HHG: bringing coherent XUV light to the lab


infrared fs-pulses

XUV

light intensity 1013-1015 W⋅cm-2

gas target

IR beam block

E.A. Gibson, Science 302, 98 (2003)

Slide 4

Limitations • conversion efficiency 10-8 to 10-6 • typical fs-amplifier: 10 W, 1 kHz

flux too low for many applications kHz repetition rate:

no frequency combs, limited usefulness

HHG: bringing coherent XUV light to the lab

Extreme nonlinear up-conversion of IR fs-pulses in gas target • broad range of coherent UV-XUV radiation • attosecond duration


HHG in enhancement cavities

Jones, et al., Phys Rev. Lett. 94, 193201 (2005) Gohle, et al., Nature 436, 234 (2005)


ERC MegaXUV: intra-laser high harmonic generation

laser gain

XUV

passive pulse formation

gas target


Minimum pulse duration of Yb-doped bulk lasers and TDLs


Average power and intracavity peak power of ultrafast TDLs


IIBS Coatings


Expect: Numerous applications in the area of NLO

→ Pulse compression to few-cycle pulses at 100s W average power

→ HHG, Intra-laser HHG, UV generation, Mid-IR generation, THz generation, ...

Expect: higher pulse energy > 100 µJ and higher average power > 1000 W

→ Longer cavities, spot size scaling, novel SESAM designs, better dispersive mirrors, …

TDLs achieve highest energy & power from ultrafast oscillators

→ Succesful energy scaling in vacuum environment: 80 µJ, 242 W, 1.07 ps, 3 MHz

Pulse compression at high energy in Kagome HC-PCFs

→ 100 W compressed with sub-200 fs pulses with 80% total compression efficiency

Excellent stability

→ CEO stabilization of TDL achieved (see talk tomorrow)

Conclusion: high power thin disk laser oscillators & NLO


Acknowledgments

ETH ULP group of Prof. Ursula Keller

UniNE LTF group

Documents

Non-linear optics