ElectroOptic Bunch Length Monitor David Fritz LUSI Motivation

Electro-Optic Bunch Length Monitor David Fritz LUSI

Motivation • Non-invasive absolute bunch length monitor - Transverse deflection cavities are invasive - Transition radiation monitors do not yield the absolute bunch length • Non-invasive time of arrival diagnostic (real time jitter measurement)

Electromagnetic Fields of the SPPS Electron Bunch • Approximate field assuming: – (close to bunch) – Steady-state 3. 4 n. C • For bunch propagating with electromagnetic field indistinguishable from a pulse of plane polarized electromagnetic radiation

Electro-Optic Effect index ellipsoid

DC Linear Electro-Optic Effect (Pockels) +V p polarized s polarized EO crystal -V Polarizer

Optical Setup

SPPS EO Chamber • EOS crystal on rotary actuator allows experimentation with different materials

EOS Bunch Length Measurement EO Crystal

Spatially Resolved Electro-Optic Sampling (EOS) Laser probe earlier later relative toto electron bunch EO Crystal

time Spatially Resolved EOS Detection polarizing beamsplitter time; space integrated intensity Arrival time and duration of bunch is encoded on profile of laser beam

Single-Shot EOS Data at SPPS (100µm Zn. Te)

EOS measure of e- bunch compression resolution limited by crystal

Single-Shot EOS Data at SPPS (100µm Zn. Te)

The jitter problem for multi-shot acquisition Master Clock Reference RF Electron Gun Accelerating Elements Sources of Short Term Jitter • RF distribution • e-beam phase to RF phase • End Station Laser phase to RF phase Limited to ~ 1 ps ! RF Distribution Network Experimental Pump Laser

Indirect X-ray Pulse Arrival Time at SPPS D undulator osc. amp EXP A. Cavalieri et al. , Phys. Rev. Lett. 94 144801, 2005

Timing jitter in electron beam used for random sampling

Temporal Resolution Limitations 1. Probe pulse duration

Effect of Long Pulse Probe Laser • Probe pulse longer than e-bunch – EO signal will be broadened – If probe pulse shape is very well known, we should be able to deconvolve e-bunch shape – Signal to background problems introduced • Probe pulse uncompressed (~10’s of picoseconds or longer) – Measurement will yield no spatially dependent signal

Temporal Resolution Limitations • Probe pulse duration • Imaging

EO crystal imaging CCD • 10 fs = 6 um extent across EO crystal at 30° incidence angle • Vacuum ports and other optics reduce angular resolution • Object does not lie in a plane perpendicular to optical axis • High resolution is required over a large depth of field (for adequate single-shot window)

Diffraction Effects in EOS Signal • EO crystal and effect combine to behave like a rectangular slit in the laser probe with single-lens imaging S-polarized P-polarized

Temporal Resolution Limitations • Probe pulse duration • Imaging • EO Crystal Properties

Frequency components of a 50 fs half-cycle pulse + • Typical EO materials are ionic crystals and have a phonon resonance somewhere in this frequency range. Ω F+ - FE (ω=Ω)

Optical Dispersion Relation Attenuation

THz Pulse in the EO Sensor FFT R, Absorption IFFT

AC EO Effect & Phase-Matching

Zn. Te Phase-Matching Characteristics • 1 st phonon resonance at ~ 5. 3 THz • EO frequency response to ~ 4 THz

Ga. P Phase-Matching Characterisitcs • 1 st phonon resonance at ~ 11 THz • EO frequency response to ~ 8 THz

Outlook SPPS LCLS Bunch Charge 3. 4 n. C 1 n. C Lorentz Factor 55, 000 (28. 5 Ge. V) 26, 600 (13. 6 Ge. V) Bunch Duration (FWHM) 80 fs 250 fs 300 MV/m 30 MV/m Peak E field at 1 cm

Femtosecond Fiber Laser Systems SPPS EO Laser Menlo Systems Pulse Duration (FWHM) 100 fs < 60 fs Pulse Energy 10 p. J > 170 p. J 800 nm 780 nm Center Wavelength

A new EO material? EO coefficient 3 x greater than Zn. Te and 12 x Ga. P But what is the frequency response?

Acknowledgements D. A. Reis 1, 2, B. Adams 3, R. Akre 4, J. Arthur 5, C. Blome 6, P. H. Bucksbaum 4, 7, A. L. Cavalieri 8, S. Engemann 5, S. Fahy 9, R. W. Falcone 10, P. H. Fuoss 11, K. J. Gaffney 5, M. J. George 5, J. Hajdu 12, P. B. Hillyard 13, M. Horn-von Hoegen 14, M. Kammler 15, J. Kaspar 13, P. Krejcik 4, S. H. Lee 1, A. M. Lindenberg 5, B. Mc. Farland 7, D. Meyer 13, T. Montagne 4, E. D. Murray 9, Nelson 16, M. Nicoul 14, R. Pahl 17, J. Rudati 3, H. Schlarb 6, D. P. Siddons 18, K. Sokolowski-Tinten 14, Th. Tschentscher 6, D. von der Linde 14 & J. B. Hastings 5 1 FOCUS Center, Departments of Physics and Applied Physics Program, University of Michigan 2 PULSE Center, Stanford Linear Accelerator Center 3 Advanced Photon Source, Argonne National Laboratory 4 Stanford Linear Accelerator Center 5 Stanford Synchrotron Radiation Laboratory/SLAC 6 Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany 7 Departments of Physics and Applied Physics, Stanford University 8 Max-Planck-Institute of Quantum Optics, Garching, Germany 9 Department of Physics and Tyndall National Institute, University College, Cork, Ireland 10 Department of Physics, University of California, Berkeley 11 Materials Science Division, Argonne National Laboratory 12 Department of Cell and Molecular Biology, Biomedical Centre, Uppsala University, Sweden 13 Department of Chemistry, Stanford University 14 Institut fur Experimentelle Physik, Universitat Duisburg-Essen, Germany 15 Institut fur Halbleitertechnologie, Universitat Hannover 16 Lawrence Livermore National Laboratory 17 Consortium for Advanced Radiation Sources, The University of Chicago 18 National Synchrotron Light Source, Brookhaven National Laboratory This work was supported in part by the: US Do. E, BES NSF FOCUS physics frontier center Stanford PULSE center Swedish Research Council Irish Research Council Science Foundation Ireland Keck Foundation Deutsche Forschungsgemeinschaft