Coherent Synchrotron Radiation Studies and Applications at the NSLS G. Lawrence Carr National Synchrotron Light Source Brookhaven National Laboratory in collaboration with D. Arena, Y. Shen, T. Watanabe, R. Lobo, D.B. Tanner, H. Loos, B. Sheehy, C.-C. Kao, S.L. Kramer, B. Podobedov, J.B. Murphy & X.-J. Wang NSLS / Brookhaven National Laboratory operated for U.S. Dep’t of Energy under contract DE-AC02-98CH10886 UVSOR Workshop on Terahertz Coherent Synchrotron Radiation Inst. for Molecular Science, Nat’l Inst. of Nat. Science, Okazaki, Sept. 23-25, 2007
Outline • Coherent synchrotron radiation from the NSLS VUV/IR storage ring: – Far-infrared spectroscopy at beamline U12IR – CSR bursts in the ~ 100 GHz spectral range. • Coherent transition radiation from the NSLS Source Development Laboratory linac: – large THz radiation pulses. – electro-optic measurement setup to sense waveforms/fields – issues when fields are large (time-dependence) – non-linear optics application: phase modulation to control spectral content, chirping, etc. • Potential application: – switching behavior in ferroelectrics, ferromagnets, superconductors. UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
Outline • Coherent synchrotron radiation from the NSLS VUV/IR storage ring: – Far-infrared spectroscopy at beamline U12IR – CSR bursts in the ~ 100 GHz spectral range. • Coherent transition radiation from the NSLS Source Development Laboratory linac: – large THz radiation pulses. – electro-optic measurement setup to sense waveforms/fields – issues when fields are large (time-dependence) – non-linear optics application: phase modulation to control spectral content, chirping, etc. • Potential application: – switching behavior in ferroelectrics, ferromagnets, superconductors. UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
Coherent Synchrotron Radiation (CSR) • 1st observations in linacs: – Nakazato et al (PRL ‘89), Happek et al (PRL ‘91) • As a linac bunch diagnostic: – Shibata et al (PRE ‘94), Lai et al (PRE ‘94), Yan et al (PRL ‘00) • As a THz source – Ishi et al (PRA ‘91), Takahashi et al (RSI ‘98), Carr et al., (Nature ‘02) • CSR also from storage rings – Arpe et al, Carr et al, Anderson et al, Abo-Bakr et al., ALS, SPRing-8, MIT/Bates, ... UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
NSLS Storage Rings X-ray ring 2.8 GeV 300ma VUVIR ring 0.8 GeV 1000 ma, 53 MHz RF, 500ps RMS bunch length UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
U12IR - beamline / spectrometer e bolometer Source point UHV Mirror M3 cone chop window lamellar Mirrors M1 and M2 grating interferometer UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
Coherent synchrotron radiation: Beam current dependence • First observed: October 1997. I 2 dependence beyond threshold. • threshold depends on operating parameters (E, bunch stretching, α ). • – G.L. Carr et al, PAC-99, SPIE: vol. 3775 p.88 (1999), Nucl. Instrum. & Meth. Phys. Res. A 463 , 387 (2001) 1000 2 I ~ Detector signal [mV] S 100 10 S ~ I 1 10 100 Beam current [ma] UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
VUV Ring Coherent SR: Relative Spectral Intensity UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
CSR Emission Bursts • Quasi-periodic bursts • Risetime < 100 µ s for α = α o • T ~ 1 to 10 ms • increases with decreasing α • detector-limited fall time 4 20 f s =12kHz f s = 1kHz Detector Signal [arb.] Detector Signal [arb.] 3 15 2 10 1 5 0 0 0 20 40 60 80 100 0.0 0.5 1.0 1.5 2.0 Time [ms] Time [ms] UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
Coherent Bursts: Time Structure (spectrum analysis) UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
Outline • Coherent synchrotron radiation from the NSLS VUV/IR storage ring: – Far-infrared spectroscopy at beamline U12IR – CSR bursts in the ~ 100 GHz spectral range. • Coherent transition radiation from the NSLS Source Development Laboratory linac: – large THz radiation pulses. – electro-optic measurement setup to sense waveforms/fields – issues when fields are large (time-dependence) – non-linear optics application: phase modulation to control spectral content, chirping, etc. • Potential application: – switching behavior in ferroelectrics, ferromagnets, superconductors. UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
The NSLS Source Development Lab Linac X.-J. Wang et al � Photocathode gun produces ~ 0.84nC (5x10 9 electrons) per “shot” photocathode dipole chicane off-crest ~ 300 fs ~ 200MeV e - gun compressor section electron bunches THz 266 nm ~ 4 ps ~ 4 ps 4 ps THz ~ 300 fs chirped “mono” 800 nm 150 fs pulses ~ 150 fs Ti:S oscillator, amplifier, harmonic gen. � Coherent output to over 1 THz. Potential for shorter bunches with less charge. � Low rep. rate (1 to 10 Hz) UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
Transition Radiation from Relativistic Electrons Metal electrons in metal respond to time-varying Coulomb field & radiate e θ ~1/ γ θ ~1/ γ relativistic e beam e note: radial source size ~ λγ => Rayleigh range ~ λγ 2 UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
Coherent THz Pulses ⎡ ⎤ ⎛ ⎞ 2 2 e Transition Radiation: Energy per electron per ω → ⎜ ⎟ ln 1 = − ⎢ ⎥ E ⎜ ⎟ 1 π c ⎝ − β ⎠ ⎣ ⎦ 10 10 electrons, 116 MeV coherent to 1 THz (Happek et al, PRL) => pulse energy of 400 µ J Expected behavior 1 0 @ Focus spectra using Far-Field movable electron beam “conventional” mirror FTIR spectrometer 8 THz Intensity [arb.] radiation quartz window 6 pyroelectric pulse 4 energy detector 2 Finite source and aperture, quartz window reflection => ~ 35% efficient or 140 µ J. 0 0 2 0 4 0 6 0 We have measured 100 µ J per pulse. -1 ] F re q u e n c y [c m UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
THz Characterizion: Electro-Optic Methods Coherent detection setup for measuring THz waveforms using Pockels Effect: “THz Electro-Optic switch” ( Zhang et al, Heinz et al ) ⎡ ⎤ ⎛ ⎞ ⎛ ⎞ 2 π 2 L π ( ) ⎥ ( ) [ ( ) ] n ~ cos ⎜ ⎟ ⎜ ⎟ − ω + ∆ φ ∆ φ = ∆ E z t t where t n E t ⎢ λ 0 ⎝ ⎠ ⎝ λ ⎠ laser ⎣ E ⎦ E THz 0 0 Electro-optic material (ZnTe) acts as a “variable waveplate” E-field ~300 fs signal ZnTe THz E(t) sampling pulse λ /4 polarizer polarizing splitter L 2 ( ) ( ) ( ) ( ) 2 dE d E ½ K = + − + − + E t E t t t t t 2 0 dt o o dt Result: Detector signal gives instantaneous THz E-field. UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
THz Characterizion: Electro-Optic Methods Coherent detection setup for measuring THz waveforms using Pockels Effect: “THz Electro-Optic switch” ( Zhang et al, Heinz et al ) ⎛ ⎞ 2 π L [ ( ) ] ( ) [ ( ) ] ~ cos ⎜ ⎟ + ∆ φ − ω ∆ φ = ∆ E kz t t where t n E t ⎝ λ ⎠ laser E E THz 0 Electro-optic material (ZnTe) acts as a “variable waveplate” ~300 fs ZnTe THz E(t) sampling video camera pulse λ /4 polarizer polarizer L Result: Snapshot of instantaneous THz E-field. 2 ( ) ( ) ( ) ( ) 2 dE d E ½ K = + − + − + E t E t t t t t 2 0 dt o o dt UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
Electro-optic sampling of SDL Linac Coherent THz Pulses Low charge (intensity) measurement: Single-cycle at focus: note that Transition Radiation is radially polarized Jitter (~ 150 fs) limits ability to extract detailed waveforms & spectra. Need a “single-shot” method Single shot image of E H Time slices 80 1 60 40 Y-Position [mm] 20 Electric Field (kV/cm) 0 0 -20 -40 -1 -60 -80 -1 0 1 X-Position [mm] UVSOR Workshop on THz Coherent Synchrotron Radiation 23-25 September 2007, IMS Okazaki, Japan BROOKHAVEN SCIENCE ASSOCIATES
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