Timing Issues for the BESSY Femtoslicing Source

Transcription

1 ICFA Workshop on Future Light Sources, Hamburg, May 15-19th, 2006 Timing Issues for the BESSY Femtoslicing Source Shaukat Khan, University of Hamburg R. Mitzner, University of Münster T. Quast, BESSY/Berlin - laser-electron timing ps and ns level - pump-probe timing fs level

2 Femtosecond laser slicing [1] electron bunch fs laser pulse fs x-ray pulse modulator dipole magnet radiator aperture electric field λ = λ 2( E (1 K 2 / m) undulator laser + 2 / 2) transverse velocity [1] A. A. Zholents, M. S. Zoloterev, PRL 76 (1996), 912.

3 Femtosecond laser slicing [1] electron bunch fs laser pulse fs x-ray pulse modulator dipole magnet radiator aperture [1] A. A. Zholents, M. S. Zoloterev, PRL 76 (1996), 912.

4 Femtosecond laser slicing worldwide fall 2001 a) ALS early experiments b) ALS upgrade 2005/2006 c) BESSY spring 2004 spring 2006 d) SLS ALS(new) BESSY SLS beam energy (GeV) photon energy (kev) separation scheme spatial angular angular pulse length (fs, fwhm) photons/pulse (0.1% bw) repetition rate (khz) laser pulse energy (mj)

5 pump beamline X-ray beamline UE-56 T B1 B2 D B3 laser beam amp P1 P m THz beamline U-139 UE-56 U m

6 Laser-electron timing (1) oscillator and storage-ring rf for 83.3 MHz = 500 MHz / 6 (2) amplifier pulse selection - pump laser timing - Pockels cell timing wavelength 800 nm pump laser Coherent Verdi V5 Ti:Sa oscillator KM-Labs MTS 5 nj 83 MHz pump laser Quantronix 527 DQE-S Ti:Sa amplifier KM-Labs HAP-AMP 2.8 mj 1 khz energy modulation pulse length 40 fs FWHM pump pulse 500 MHz bunch clock pulse selection intrinsic synchronization sin( ωt + ϕ) cos( ωt) = 1 2 ϕ 2 { sin( ϕ) + sin(2ωt + ϕ) } + K

7 Laser-electron timing (1) oscillator and storage-ring rf for 83.3 MHz = 500 MHz / 6 (2) amplifier pulse selection - pump laser timing - Pockels cell timing Requirements: better than longitudinal mode-zero bunch oscillations ~ 3 ps (0.5 deg rf) for 15 ps rms bunch length ~ 2% electron density change Specified jitter: less than 250 fs Measured: less than 1 ps (spectrum analyzer) Tuning: (a) 6-fold ambiguity: trial and error, checked by scope (ns) (b) two trombones (one manual, one under EPICS control) ~ 100 ps by 2 GHz digital scope in persistence mode ~ 3 ps by maximizing THz or photon signal

8 Diagnostics of laser-electron interaction Longitudinal electron distribution coherent THz radiation [1] U-139 UE [1] K. Holldack et al., Part. Acc. Conf., Knoxville (2005), 2239.

9 May 9/10, 2006: first sub-picosecond slicing Alignment mode 3mA single bunch laser: 1mJ, 50fs User operation mode 300mA multi-bunch + 3mA camshaft laser: 2.5mJ, 50fs courtesy: G. Ingold, SLS

10 Laser-electron timing (2) amplifier pulse selection - pump laser timing - Pockels cell timing SRS DG535 Delay Generator 1 ppm Trigger A (4) Trigger Output Delay A 50 Ω, EXT, Thr -0.3 V, neg. Slope 50 Ω, NIM, inverted 998,100.0 ns for single bunch 5 x 1.25 MHz (NIM) 2. GATE end marker (5) select every ~83000-th pulse (i) counting oscillator pulses (ii) set a precise delay (1 ppm) OR out (1) 1. GATE out (2) AND out out (3) moving the switch to the right starts the loop (left)(stops) NIM/TTL switch: "out" SRS DG535 Delay Generator 25 ppm Trigger 20 ns 5 x 1.25 MHz signal (1) Pump laser Pockels cell 140 ns 140 ns output of 1. GATE(2) 140 ns 140 ns 40 ns AND = DG535 trigger (3) DG535 BUSY t A ~ 1 ms 800 ns 750 ns DG535 output A (4) output of 2. GATE end marker of 2. GATE (5)

11 Laser-electron timing (2) amplifier pulse selection - pump laser timing - Pockels cell timing SRS DG535 Delay Generator 1 ppm Trigger A (4) Trigger Output Delay A 50 Ω, EXT, Thr -0.3 V, neg. Slope 50 Ω, NIM, inverted 998,100.0 ns for single bunch 5 x 1.25 MHz (NIM) 2. GATE end marker (5) select every ~83000-th pulse (i) counting oscillator pulses (ii) set a precise delay (1 ppm) OR out (1) 1. GATE out (2) AND out out (3) moving the switch to the right starts the loop (left)(stops) NIM/TTL switch: "out" SRS DG535 Delay Generator 25 ppm Trigger 20 ns 5 x 1.25 MHz signal (1) Pump laser Pockels cell 140 ns 140 ns output of 1. GATE(2) 140 ns 140 ns 40 ns t A ~ 1 ms 800 ns 750 ns AND = DG535 trigger (3) DG535 BUSY DG535 output A (4) output of 2. GATE end marker of 2. GATE (5) Diagnostics: pump laser timing - max. amplifier power Pockels cell timing - single/double pulse

12 First pump-probe experiments (preliminary) C. Stamm, T. Kachel, N. Pontius, R. Mitzner, T. Quast, K. Holldack, S. Khan, C. Lupulescu, H. Dürr, W. Eberhardt (BESSY) UE56/1 sliced 1000 Hz sample probe pulse delay 500 Hz chopper APD pump pulse laser 1000 Hz 500 Hz trigger disc disc AND delay generator signal counter 1 (pumped) 0 1 ms counter 2 (not pumped)

13 Time resolution ~ 150 fs Assumed pulse duration 100 fs (FWHM), pulse lengthening: - monochromator (wavelength illuminated lines < 30 fs) -1 o angle between pump and probe pulse pump 18 mrad 1mm e.g. = c 60 fs probe - path length changes over 8 hrs and 40 m e.g. 30 μm/ c = 100 fs pump pulse x-ray e photo: K. Godehusen

14 Acknowledgements H. Bäcker, J. Bahrdt, H. Dürr, V. Dürr, W. Eberhardt, K. Godehusen, A. Gaupp, K. Holldack*, E. Jaeschke, T. Kachel*, S. Khan*, D. Krämer, C. Lupulescu*, R. Mitzner*, M. Neeb, W. Peatman, N. Pontius*, T. Quast*, G. Reichardt, M.-M. Richter, M. Scheer, O. Schwarzkopf, F. Senf, C. Stamm*, G. Wüstefeld (BESSY, Berlin) I. Hertel, F. Noack, W. Sandner, I. Will, N. Zhavaronkov (MBI, Berlin) *) commissioning team Useful discussions with R. Abela, P. Beaud, G. Ingold, A. Streun (PSI, Villigen), P. Heimann, R. W. Schoenlein, A. Zholents, M. Zoloterev (LBNL, Berkeley) S. Backus, D. Müller, K. Read, (KMLabs, Boulder) Funded by the Bundesministerium für Bildung und Forschung and by the Land Berlin