Embed Size (px)
Citation preview
Intense Terahertz Sources for Time-resolved Study of Matter
Haidan WenX‐ray Science Division
Argonne National Laboratory
Acknowledgements
Slides credits to:K. Nelson, S. Kaiser, R. Huber, A. Lindenberg, J. Helbing, J. Dai, D. Xiang, G. Williams. H. Hama, M. Gensch,, A. Fisher, A. Perucchi, S. Biedron, E. Chiadroni, K. Bane, J. A. Fulop, K. Y. Kim, E. Landahl,J. Byrd, K. J. Kim, A. Zholents, A. Cavalleri, and more …
Workshop on Terahertz Sources for Time Resolved Studies of MatterJuly 30‐31, Argonne National Laboratory
2
Outline
Science drivers Intense THz sources
– Accelerator based sources– Laser based sources
THz pump, X‐ray probe technique Conclusion
3
Electronic excitation
Optical
THz
Motivation: Enabling collective excitation
E
Engineering electronic ground state at ultrafast time scale
Spin
Charge
Lattice
Orbital
4
Science drivers
Impulsive excitation (broad band)– Control electrons in Rydberg atoms– Impact & tunneling ionization– Driving polarization in polar materials – Magnetic switching– Molecular alignment– Field induced phase transition
Resonant excitation (narrow band)– Excitons, plasmons…– Coherent lattice motion– Coherent spin wave– Superconducting gaps
VO2
Nelson and Averitt groupMetal‐insulator phase transition:
Liu, Nature, 487, 345 (2012)
La1.675Eu0.2Sr0.125CuO4
Cavelleri groupInduce superconductivityD. Fausti, et al, Science 331, 189 (2011)
Examples:
5
How intense is intense?
Wish list for intense THz sources (“processed data”):
Broad Band Narrow band
Pulse energy 100uJ 100uJ
Peak field >10MV/cm >1MV/cm
Pulse duration < 1ps ~ ps
Spectrum range: Tunable, 0.1 – 10 THz Tunable, 0.1 – 100THz
Spectrum width: Tunable, 0.1 – 10 THz 1% of the band width
Repetition rate: MHz
Intense enough to drive desired dynamics
6
Intense THz sources
Accelerator based:– Coherent transition radiation – Coherent synchrotron radiation– Wave field acceleration in dielectric structures
– Smith‐Purcell radiation Laser based:
– Optical rectification– Air plasma– Photoconductive switch– Laser wave field
James Clerk Maxwell
7
)())(1( 2 fNfNP
Coherent Synchrotron Radiation (CSR) Coherent Transition Radiation (CTR)
e‐ Foil
Accelerator-Based Coherent THz emission
incoherent coherent
Other mechanism: Backward Wave Oscillators, Cerenkov‐FELs, Smith‐Purcell radiation, …
2/ˆi n z cf e S z dz
8
CSR Low alpha mode to reduce electron bunch length Pro: potential high repetition rate for synchronized X‐ray probe Con: unstable, interdependent on other beamlines
CSR / CTR Easy control of accelerator parameters Pro: high peak current for high THz pulse energy Con: low repetition rate unless superconducting cavity $$$
Implementation:
Storage ring based:
Single‐pass accelerator based:
Ex: Sparc_lab@Italy
Ex: Circe@USA, proposal
9
10
Modulating e‐beam before radiation
Bielawski et al., Nature. Phys, 2008
Xiang, et. al., PRL, 108, 024802 2012
UV laser
Gun
Narrow-band THz from CTR
Conjugate pipe TPIPE, K. Bane
Dielectric Layer Acceleration S. Antipov, et. al., PRL 108, 144801 (2012)
Modulating electron bunch
Modulating photoinjection laserShen, et. al., PRL 107, 204801 (2011)
Modulating e‐beam during radiation
Accelerator
Summary: Accelerator based THz sources
Freq. (THz)
Mechanism Pulse energy
Pulse duration Rep Rate
Single pass accelerator
UCSB, USA 0.12‐10 CSR 1mJ 1‐20us <7.5Hz
Brookhaven, USA 0.1‐2 CTR 80uJ <1ps 2.5Hz
FLASH, Germany 1‐30 CTR/CSR <100uJ ~10ps (micro) 1MHz (micro) 5Hz (macro)
ELBE, Germany 0.1‐3 CTR/CSR 1‐100uJ <ps 100‐500kHz/13MHz
LCLS, USA 0.1‐40 CTR 140uJ <1ps 120Hz
Tera Fermi, Italy (proposal)
0.1‐10 CTR/CSR 10uJ <1ps 30Hz (?)
SPARC, Italy 0.1‐ 5 CTR/CSR 20/ 0.6uJ
0.2ps/ 10Hz
FACET,NLCTA@SLAC, USA
0.5‐ 5 CTR ~500uJ <1ps 10‐30Hz, 1kH
Storage ring BESSY II, Germany 0.1‐1 CSR <nJ ~ps 1.25MHz ‐500MHz
CIRCE, USA(proposal)
0.03‐ 30 CSR 10uJ ~ps 91.1kHz
t‐ACTS, Japan(construction)
0.1‐ 10 CTR/CSR <5uJ ~20ps (micro) 2us (macro)
2856MHz (micro pulse)10Hz (macro pulse)
Jlab (ERL), USA 0.1‐ 5 CTR/CSR ~1uJ <1ps 75MHz
Partial list
11
12
Complications: • Interdependence on accelerator• Timing structure• Radial polarization from CTR ‐>
longitudinal polarized at the focus
Advantages:• High pulse energy, • Potential high repetition rate, • Sync with accelerator based x‐ray source
Summary: Accelerator based THz sources
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
103
104
Ene
rgy
per p
ulse
(uJ)
0.001 0.01 0.1 1
Energy (eV)
0.1 1 10 100
Frequency (THz)
IR FEL's / Undulators
CSRStorage-Rings
J-Lab
CTR, LCLS, FERMI, etc
© Perucchi
FLASH timing structure Radial polarized THz from CTR
Laser based THz sources: Broadband
13
Opitcal pulse
+ ‐J
Nonlinear crystal
Air Plamsa
Photoconductive switch
Break symmetry
THz pulse
Optical rectification technique
14
Organic crystlal: DAST
Large aperture crystal
ZnTe, Diameter 75mm, Pump: 800nm, 70mJ, 100Hz
C. P. Hauri, et. al. Appl. Phys. Lett. 99, 161116 (2011)
Blanchard, IEEE, J. Select. Top. Quan. Electron. 17, 5 (2011)
Pump: 1.2‐ 1.5 um, 900uJ, 100Hz, phase matched
15
Optical Rectification – Pulse Front tilt
Phase matching!!
~10uJ, Yeh, et. al., APL, 90, 171121 (2007)
ω+δω ‐δ
©R. Huber
2δ
©J. Fulop
Optimization of Tilted Pulse Front technique
16
Pump pulse: longer pulse, longer wavelength
Desensitive dispersion Suppress crystal damage Reduce walk‐off
Crystal: lower temperature optimize the length
4f imaging:
Reduce THz absorptionIncrease interaction length
BenefitBenefit
50uJ, Stepanov, et. al., Appl. Phys. B, 101, 11 (2010) 125uJ, Fulop, et. al., OL, 37, 557 (2012)
Better focusing close to diffraction limit
<10uJ, ~1.2MV/cm, Hirori, et. al., APL, 98, 091106 (2011)
©J. Fulop
e
LensTHz pulse
THz generation in air plasma:
plasma
No Bias: Single color pump : H. Hamster, et al. PRL, 17, 2725 (1993), Plasma, ponderamotive force
DC bias: Electrodes,
Loffler, et. al. APL, 77, 453 (2000); Houard, et. al. PRL 100, 255006 (2008)
AC bias: Two Color pump: D. J. Cook et. al. Opt. Lett. 25, 1210 (2000), First demonstration T. Bartel, et. al. Opt. Lett. 30, 2805 (2005), High field achieved Kim, et. al. OE 15, 4577 (2007), Nat. Photon., 2, 605 (2008), photocurrent model, Karpowicz, PRL 102, 093001 (2009), Quantum model Xie, et. al. PRL 96, 075005 (2006) ;Wen et. al. PRL 103, 023902 (2009) , Dai, et. al. PRL 103, 023001
(2009), Coherent control Dai, et. al. PRL, 97, 103903 (2006) Ultrabroad band generation and detection.
SHG
2
E
1uJ, 1MV/cm
∝©K. Kim
©J. Dai
17
18
Laser based THz sources: Narrow band
©R. Huber
Sell, Opt. Lett. 33, 2767 (2008)
Chen, et. al., APL, 99, 071102 (2011)
©K. Nelson
1) Diff. Freq. Generation
2) Pulse shaping +O.R.
19uJ@30THz
1uJ
Summary: Laser based source
19
Techniques Freq. (THz) Bandwidth Pulse energy Pulse duration
Rep Rate
Optical Rectification
Pulse front tilt 0.12‐10 Broad <125uJ, 1MV/cm
1‐20us 100Hz
Phase locked narrow band 0.1‐2, or 10‐100
Narrow(10%BW)
1.5uJ@1THz~19uJ@30THz
~1ps 1kHz
Large crystalBlanchard, et.al. IEEE, J. STQE. 17, 5 (2011)
0.1‐2 Broad <2uJ <1ps 100Hz
Organic DASTC. P. Hauri, et. al. APL, 99, 161116 (2011)
0.1 ‐5 Broad <20uJ <1ps 100Hz
Air plasma Two‐color 0.1‐60 Broad ~1uJ, 1MV/cm <ps 1kHz
Advantages:• Compact• Independent of the accelerator sources• Linearly polarized (most of the case)• Better focusing
Challenges:• High peak field• High repetition rate
Outline
Science drivers Intense THz sources
– Accelerator based sources– Laser based sources
THz pump, X‐ray probe techniques Conclusion
20
The need for THz pump, X-ray probe techniques
X‐ray probes structures with atomic resolution and element specificity
sin2d
X-ray Diffraction X-ray Absorption
THz excites structural dynamics
VO2
Metal‐insulator phase transition: Liu, et. al., Nature, 487, 345 (2012)
La1.675Eu0.2Sr0.125CuO4
Induce superconductivityD. Fausti, et al, Science 331, 189 (2011)
21
22
Accelerator based THz-pump, X-ray probeTHz
© J. Byrd
• Same electron bunch for THz and X‐ray generation• THz pump must arrive before X‐ray probe, Delay X‐ray• Long THz transport 10‐100m
• Double bunch scheme • Independent secondary accelerator
Laser• Long transport of the pump beam• Synchronization
Laser based THz-pump, X-ray probe
THz generator
User
23
Typical user experiments @LCLS
Credit to M. Hoffmann@LCLS
Complications:• Vacuum• Geometric constrain• Timing
LCLS experimentLed by A.Cavalieri, Univ. Hamburg
THz pump, X-ray diffraction probe at Sec7, APS
24
THz pump, hard X-ray diffraction setup at 7ID-C.
800nm, 50fs, 2mJ
THz pulse, 0.5uJ 10keV, X‐ray
BBO crystal
• Pulse duration: 1‐2 ps• Flux:
1e4 photon / pulse1e11 photons /sec@10ekV, 0.01BW
• Tunability:Hard X‐ray 5‐35keVSoft X‐ray 800eV ‐2keV
• Rep rate: 6.5MHz
World’s first high-repetition rate, widely tunable, polarized short pulse x-ray synchrotron source
APS‐Upgrade (2018)Short Pulse X‐ray facility
25
Solution proposed at Argonne
• Match spatially confined excitation• Beautiful match to SPX pulse duration
1ps ‐> 1THz
2. Near field enhancement
3. Hard x‐ray nanoprobe
1. Intense THz soure
• Enhance THz field by charge concentration• 100nm slit width:1MV/cm ‐>120MV/cm!!!
Extreme field condition: 100MV/cm, 0.3ps, 100nm
Nature Liu, et. al. (2012)
Laser‐based THz source: 0.1‐1MV/cm
Nature Photonics, 3, 152 (2009)
Conclusion
26
Laser based: Accelerator based:
Pulse energy: <125uJ 1‐500uJ
Peak field: ~1MV/cm ~20MV/cm
Spectrum
broadband 0.1‐60 THz (air plasma) 0.1‐20 THz (50fs bunch)
narrowband 10‐70 THz tunable 30% BW 0.1‐10 THz
Advantages: • Compact• Independent of the
accelerator sources• Controllable pulse shape and
polarization• Better focusing
• High pulse energy,• Potential high repetition rate,• Naturally sync . with
accelerator based x‐ray source
Challenges: • High pulse energy• High repetition rate
• Interdependence on accelerator
• Timing structure• Radial polarization (CTR)
THz pump X‐ray probe capability is in development for new science
