February 17-18, 2010 R&D ERL Brian Sheehy R&D ERL Laser and laser light transport Brian Sheehy February 17-18, 2010 Laser and Laser Light Transport

February 17-18, 2010 R&D ERL Brian Sheehy Laser and Laser Light Transport 2 Laser Requirements System Description Master Oscillator Power Amplifier Temporal Shaping Spatial Shaping Transport Diagnostics & Controls

February 17-18, 2010 R&D ERL Brian Sheehy Laser Requirements 3 Rep Rate: 9.38 MHz, phase locked with 75 th harmonic, the MHz RF frequency of the superconducting cavities. Jitter < 1psec rms Wavelength: tradeoff between ease of production/shaping and attainable QE Lambda (nm) Laser Power QE (CsK 2 Sb)max current W~1%43 mA 3555 W~10%143 mA Temporal Shape: 50 psec flat top, 10 psec rise  Spatial Shape: Flat top, 1e-6 pedestal

February 17-18, 2010 R&D ERL Brian Sheehy Laser Specifications 4 Master RF Repetition Rate703.5 MHz Laser PRF (Phase II for RHIC II)9.38 MHz Frequency tunability+/- 1 MHz Synchronization deviation to master oscillator<1 ps rms Pulse Length5-12 ps FWHM Jitter in pulse length0.1 ps Final Output wavelength355 nm Optional output wavelength532 nm Beam 355 nm TEM 00 ; M 2  1.5 Optimized for a required power at 355 nm>5 W Average output power stability at 355 nm< 1% rms Amplitude noise< 1% rms Centroid Position StabilityLess than 3% of the beam radius (1/e 2 level) Pointing StabilityLess than 25 microradian Pre- and post-pulses and pedestals, temporal haloLess than 0.5% of total UV energy within +/-100 ps of laser pulse The stability, rep-rate and power requirements motivated the choice of a master oscillator – power amplifier (MOPA) configuration based on Nd:YVO 4 (1064 nm), with subsequent frequency multiplication.

February 17-18, 2010 R&D ERL Brian Sheehy Laser Diagram White Cell folded cavity oscillator Passively mode-locked with semiconductor saturable absorber mirror (SESAM) NdYVO4 MOPA pumped by off-board diodes 1064 nm fundamental SHG 532 nm, THG 355 nm (color indicates point of generation /amplification in figure to the left) Electro-optic pulse picking single to 1 kHz bunch rate single pulse to 90% duty cycle within bunches or CW 9.38 MHz fits in a 130 x 55 cm enclosure

February 17-18, 2010 R&D ERL Brian Sheehy Laser Performance Summary 6

February 17-18, 2010 R&D ERL Brian Sheehy 7

February 17-18, 2010 R&D ERL Brian Sheehy Pulse Shaping 8 A long, flat topped (in both space and time) pulse is desired, in order to avoid emittance growth from space-charge forces the limited bandwidth of picosecond pulses rules out coherent temporal shaping methods pulse stacking birefringent interferometric

February 17-18, 2010 R&D ERL Brian Sheehy 9 Pulse Stacking for Temporal Shaping Sharma et al PRSTAB 2009 Tomizawa et al Quant Elec 2007 Birefringent Method Interferometric Method No adjustable parameters Crystal length and quality issues Extremely sensitive to alignment Stability Both stacking methods very sensitive to phase variations across the pulse variations in time chirp need better time resolution in our shape measurements derive fast pulse from dump light R&D ERL

February 17-18, 2010 R&D ERL Brian Sheehy Spatial Shaping 10 Commercially available, Gallilean telescope using aspheric lenses so that the magnification is radially dependent. Flat top to 5% very sensitive to input pulse parameters

February 17-18, 2010 R&D ERL Brian Sheehy Beam shaping test using 532 nm Light A. Sharma, T. Tsang & T Rao PRSTAB 12, (2009) 11

February 17-18, 2010 R&D ERL Brian Sheehy Beam shaping test using 532 nm Light A. Sharma, T. Tsang & T Rao PRSTAB 12, (2009) 12 Autocorrelation signal Input pulse Cross-correlation signal Shaped pulse (de-convoluted) Short/ long term stability

February 17-18, 2010 R&D ERL Brian Sheehy Diagnostics and Control 13 Timing and Stability Jitter with respect to RF master clock: phase detector filtered photodiode signal mixed with RF reference done in laser room and at gun for detecting path length fluctuations pulse pattern and power: photodiodes with gated analysis Temporal Shape cross correlation before and after temporal shaping Spatial Shape profile/position monitors at frequent intervals cameras looking at leakage or pickoffs Monument large format CCD camera placed in a focal plane conjugate to the photocathode position.

February 17-18, 2010 R&D ERL Brian Sheehy System Overview

February 17-18, 2010 R&D ERL Brian Sheehy Summary Laser & Transport do not present any critical impediments to the project Lumera Laser source meets spec need more independent testing at BNL Temporal and Spatial shaping tested in principle, with transport Current engineering issues birefringent vs. interferometric temporal shaping improve time diagnostic (ultrashort pulse) beam ellipticity (spatial filtering)