Yuelin Li Accelerator Systems Division Argonne National Laboratory

1. Distortion of single-shot EO sampling techniques in measuring particle beam profilesand SR application Yuelin Li Accelerator Systems Division Argonne National Laboratory ICFA: Frontiers of Short Bunches in Storage Rings Frascati, Italy, Nov. 7-8, 2005

2. Acknowlegement • K. -J. Kim, K. Harkay, moral, financial support • J. Wang, E. Landahl, real estate surpport • P. Bolton, X. Zhang, helpful discussion • Work supported by the U. S. Department of Energy, Office of Basic Energy Sciences, Contract No. W-31-109-ENG-38.

3. Probe laser P1 P2 e beam Measuring ultrashort electron beam using electro optical sampling Laser (001) p y x E p z (110) E beam dr: crystal residual or bias birefringence.

4. EO history and its application in beam measurement • Observation of optical rectification, 1962 Bass et al., PRL 9, 446 (1962) • Demonstration of picosecond optical sampling, 1982 Valadmanis et al, APL 41, 212, (1982) • Demonstration of single-shot EO techniques, 2000- Chirped laser pulse, Jiang and Zhang, APL 72, 1945 (1998) THz/Probe correlation, Shan et al, OL 25, 426 (2000) Double correlation, Jamison et al, OL 28, 1710 (2003) FROG EO: proposed by Bolton (2002) • Application in beam measurement, 1998- • FNAL and BNL: 100 ps- ns temporal resolution • FELIX: Yan et al., PRL 85, 3404 (2000); • FELIX: Wilke et al., PRL 88, 124801 (2002), 2 ps • FELIX: Berden et al., PRL 93, 114802 (2004), 300 fs • SLAC/SPPS: Cavalieri et al., PRL 94, 114801 (2005), 300 fs

5. What’s left? • Choice of single-shot techniques • Chirped probe pulse mapping • Probe laser cross correlation • “Real” time-resolved • Distortions and corrections for precision measurement • Identification of distortion effects • Crystal orientation? • Known effect: group velocity mismatch, crystal response • Better temporal resolution • Physical limit: crystal response and choice of techniques • Application beyond short bunch measurement for linac beam • Scenario for SR applications

6. Probe laser P1 P2 Pump laser THz Probe laser P1 P2 e beam Off-line EO testing experiment • Replace the particle beam with an EM impulse, i.e., THz pulse • Differences from a THz experiment • Particle beam fields has a zero carrier frequency • Particle beam may deliver much higher field strength • Particle beams require single-shot measurement

7. Experiment setup Adjustment optical bias dr Pump/Probe duration: 70 fs Pump Energy: 0.8 mJ/pulse Probe: 0.08 mJ/pulse Adjustment of sampling crystal angle Shan et al, Opt Lett 25, 426 (2000). 0.28 ps Adjustment of pump intensity Time

8. Effect of optical bias Raw data Background Background subtracted • The signal can be linear or nonlinear depends on the relative magnitude of drandd. • The signal can flip sign artificially!

9. Intensity distortion

10. Correction and caution • These distortion are important for near zero optical (crossed polarizer) configuration. • Recent SLAC and FELIX experiments are performed in this region • In general, correction is impossible if signal sign flipping occurs, i.e., the beam induced phase shift becomes larger than the residue/bias and has an opposite sign. • [Jiang et al., APL 74, 1191 (1999)] • To avoid artificial sign flipping and distortion • Working with large optical bias up to quarter wave to maintain linearity (balanced detector) • If have to work at near to zero bias, proper orientation of the sampling crystal is needed to make the residue in line with the expected field orientation.

11. Dependence on sampling crystal orientation: unexpected Planken eta l., JOSA B18, 313 (2001)

12. Experimental waveform at different angles Waveform at angles are completely different • First observation of orientation dependence in this geometry • May have to do with the tilt of the crystal? • Further investigation is needed

13. SR applicationsbeam profile and position monitor in 1 • Linac: obvious • SASE, etc • Storage ring: turn by turn profile monitor • Short bunch/CSR instability/CSR radiation (Kuske, Byrd) • Femto slicing (Byrd, Baeck) • Tilted beam (K. Harkay, Borland) • Microwave instability/bursting mode • Charge fluctuation • Bunch length modulation (Biscari) • Timing monitor for pump probe experiment

14. SR application example 1 • Microwave instability 40 ps rms bunch + modulation (3 ps, 2%) E beam: 12 nC Laser: 2% bandwidth @ 800 nm, stretched to 60 ps rms Crystal: 0.1 mm ZnTe @ 1 cm from the beam A 0.015% white noise is added to simulate the noise level of a 16 bit detector.

15. SR application 2: Timing monitor for pump-probe experiment • Locking the laser to the pump/probe laser • Observe the relative shift of the bunch in respect to the laser pulse Bunch oscillation in bucket by 10 ps E beam: 40 ps, 12 nC Laser: 2% BW @ 800 nm, 100 ps Crystal: 0.1 mm ZnTe @ 1 cm 0.015% white noise added to simulate a realistic situation for a 16 bit camera.

16. Summary • Distortion at near zero optical bias • Artificial flipping of field sign • Quadratic signal dependence on the field under investigation • Dependence on the orientation of the sampling crystal • Application in SR • As beam profile monitor/transverse motion monitor • As timing monitor for pump-probe experiment • …. • Future work needed: • Clarify the angular dependence of the crystal orientation • Crystal property measurement: to reach the limit of the technique