Intense Terahertz Sources for Time-resolved Study of Matter Haidan Wen X ray Science Division Argonne National Laboratory
Acknowledgements Workshop on Terahertz Sources for Time Resolved Studies of Matter July 30 31, Argonne National Laboratory 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 2
Outline Science drivers Intense THz sources Accelerator based sources Laser based sources THz pump, X ray probe technique Conclusion 3
Motivation: Enabling collective excitation THz Spin Orbital Charge Electronic excitation Lattice Optical Engineering electronic ground state at ultrafast time scale E 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 Examples: Nelson and Averitt group Metal insulator phase transition: Liu, Nature, 487, 345 (2012) VO 2 Cavelleri group Induce superconductivity D. Fausti, et al, Science 331, 189 (2011) La 1.675 Eu 0.2 Sr 0.125 CuO 4 5
How intense is intense? Intense enough to drive desired dynamics 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 6
Intense THz sources James Clerk Maxwell 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 7
Accelerator-Based Coherent THz emission P N(1 incoherent f ( )) N 2 f ( ) coherent 2 f ei nz ˆ / c Szdz Coherent Synchrotron Radiation (CSR) Coherent Transition Radiation (CTR) e Foil Other mechanism: Backward Wave Oscillators, Cerenkov FELs, Smith Purcell radiation, 8
Implementation: Ex: Sparc_lab@Italy Single pass accelerator based: CSR / CTR Easy control of accelerator parameters Pro: high peak current for high THz pulse energy Con: low repetition rate unless superconducting cavity $$$ Storage ring based: Ex: Circe@USA, proposal 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 9
Narrow-band THz from CTR Modulating electron bunch Modulating photoinjection laser Shen, et. al., PRL 107, 204801 (2011) Modulating e beam during radiation Conjugate pipe TPIPE, K. Bane Gun Accelerator UV laser Modulating e beam before radiation Bielawski et al., Nature. Phys, 2008 Xiang, et. al., PRL, 108, 024802 2012 Dielectric Layer Acceleration S. Antipov, et. al., PRL 108, 144801 (2012) 10
Summary: Accelerator based THz sources Partial list Single pass accelerator Freq. (THz) Mechanism Pulse energy Pulse duration Rep Rate 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 0.1 10 CTR/CSR 10uJ <1ps 30Hz (?) (proposal) SPARC, Italy 0.1 5 CTR/CSR 20/ 0.2ps/ 10Hz 0.6uJ FACET,NLCTA 0.5 5 CTR ~500uJ <1ps 10 30Hz, 1kH @SLAC, USA Storage ring BESSY II, Germany 0.1 1 CSR <nj ~ps 1.25MHz 500MHz CIRCE, USA (proposal) t ACTS, Japan (construction) 0.03 30 CSR 10uJ ~ps 91.1kHz 0.1 10 CTR/CSR <5uJ ~20ps (micro) 2us (macro) Jlab (ERL), USA 0.1 5 CTR/CSR ~1uJ <1ps 75MHz 2856MHz (micro pulse) 10Hz (macro pulse) 11
Summary: Accelerator based THz sources Energy (ev) Advantages: High pulse energy, Potential high repetition rate, Sync with accelerator based x ray source Complications: Interdependence on accelerator Timing structure Radial polarization from CTR > longitudinal polarized at the focus Energy per pulse (uj) 10 4 10 3 10 2 10 1 10 0 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 0.001 0.01 0.1 1 CTR, LCLS, FERMI, etc IR FEL's / Undulators J-Lab CSR Storage-Rings Perucchi 0.1 1 10 100 Frequency (THz) FLASH timing structure Radial polarized THz from CTR 12
Laser based THz sources: Broadband + J Opitcal pulse Photoconductive switch THz pulse Nonlinear crystal Air Plamsa Break symmetry 13
Optical rectification technique Large aperture crystal ZnTe, Diameter 75mm, Pump: 800nm, 70mJ, 100Hz Blanchard, IEEE, J. Select. Top. Quan. Electron. 17, 5 (2011) Organic crystlal: DAST Pump: 1.2 1.5 um, 900uJ, 100Hz, phase matched C. P. Hauri, et. al. Appl. Phys. Lett. 99, 161116 (2011) 14
Optical Rectification Pulse Front tilt J. Fulop ω δ ω+δ Phase matching!! R. Huber ~10uJ, Yeh, et. al., APL, 90, 171121 (2007) 2δ 15
Optimization of Tilted Pulse Front technique Benefit Pump pulse: longer pulse, longer wavelength Crystal: lower temperature optimize the length Benefit Desensitive dispersion Suppress crystal damage Reduce walk off Reduce THz absorption Increase interaction length 50uJ, Stepanov, et. al., Appl. Phys. B, 101, 11 (2010) 125uJ, Fulop, et. al., OL, 37, 557 (2012) J. Fulop 4f imaging: Better focusing close to diffraction limit <10uJ, ~1.2MV/cm, Hirori, et. al., APL, 98, 091106 (2011) 16
THz generation in air plasma: 2 K. Kim e plasma E Lens SHG No Bias: Single color pump : H. Hamster, et al. PRL, 17, 2725 (1993), Plasma, ponderamotive force DC bias: Electrodes, THz pulse 1uJ, 1MV/cm J. Dai 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. 17
Laser based THz sources: 1) Diff. Freq. Generation R. Huber Narrow band 19uJ@30THz Sell, Opt. Lett. 33, 2767 (2008) 2) Pulse shaping +O.R. K. Nelson 1uJ Chen, et. al., APL, 99, 071102 (2011) 18
Summary: Laser based source Optical Rectification Techniques Freq. (THz) Bandwidth Pulse energy Pulse duration Pulse front tilt 0.12 10 Broad <125uJ, 1MV/cm Phase locked narrow band Large crystal Blanchard, et.al. IEEE, J. STQE. 17, 5 (2011) 0.1 2, or 10 100 Narrow (10%BW) 1.5uJ@1THz ~19uJ@30THz 1 20us ~1ps Rep Rate 100Hz 1kHz 0.1 2 Broad <2uJ <1ps 100Hz Organic DAST C. 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 19
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 THz excites structural dynamics Metal insulator phase transition: Liu, et. al., Nature, 487, 345 (2012) Induce superconductivity D. Fausti, et al, Science 331, 189 (2011) VO 2 La 1.675 Eu 0.2 Sr 0.125 CuO 4 X ray probes structures with atomic resolution and element specificity X-ray Diffraction X-ray Absorption 2d sin 21
Accelerator based THz-pump, X-ray probe THz 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 based THz-pump, X-ray probe User Long transport of the pump beam Synchronization Laser THz generator 22
Typical user experiments @LCLS Credit to M. Hoffmann@LCLS Complications: Vacuum Geometric constrain Timing LCLS experiment Led by A.Cavalieri, Univ. Hamburg 23
THz pump, X-ray diffraction probe at Sec7, APS APS Upgrade (2018) Short Pulse X ray facility THz pulse, 0.5uJ 10keV, X ray BBO crystal 800nm, 50fs, 2mJ Pulse duration: 1 2 ps Flux: 1e4 photon / pulse 1e11 photons /sec @10ekV, 0.01BW Tunability: Hard X ray 5 35keV Soft X ray 800eV 2keV Rep rate: 6.5MHz THz pump, hard X-ray diffraction setup at 7ID-C. World s first high-repetition rate, widely tunable, polarized short pulse x-ray synchrotron source 24
Solution proposed at Argonne 1. Intense THz soure Laser based THz source: 0.1 1MV/cm 2. Near field enhancement Enhance THz field by charge concentration 100nm slit width:1mv/cm >120MV/cm!!! Nature Liu, et. al. (2012) Extreme field condition: 100MV/cm, 0.3ps, 100nm Nature Photonics, 3, 152 (2009) 3. Hard x ray nanoprobe Match spatially confined excitation Beautiful match to SPX pulse duration 1ps > 1THz 25
Conclusion Laser based: Accelerator based: Pulse energy: <125uJ 1 500uJ Peak field: ~1MV/cm ~20MV/cm Spectru m 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 26