Laser and Laser Light Transport RD ERL Laser

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

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

Laser Requirements R&D ERL Rep Rate: 9. 38 MHz, phase locked with 75 th harmonic, the 703. 5 MHz RF frequency of the superconducting cavities. Jitter < 1 psec rms Wavelength: tradeoff between ease of production/shaping and attainable QE Lambda (nm) QE Laser Power (Cs. K 2 Sb) max current 532 10 W ~1% 43 m. A 355 5 W ~10% 143 m. A Temporal Shape: 50 psec flat top, 10 psec rise Spatial Shape: Flat top, 1 e-6 pedestal Brian Sheehy 3 February 17 -18, 2010

Laser Specifications R&D ERL 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. Master RF Repetition Rate 703. 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 Length 5 -12 ps FWHM Jitter in pulse length 0. 1 ps Final Output wavelength 355 nm Optional output wavelength 532 nm Beam Quality @ 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 Stability Less than 3% of the beam radius (1/e 2 level) Pointing Stability Less than 25 microradian Pre- and post-pulses and pedestals, temporal halo Less than 0. 5% of total UV energy within +/-100 ps of laser pulse Brian Sheehy 4 February 17 -18, 2010

Laser Diagram R&D ERL • White Cell folded cavity oscillator • Passively mode-locked with semiconductor saturable absorber mirror (SESAM) • Nd. YVO 4 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 k. Hz bunch rate • single pulse to 90% duty cycle within bunches • or CW 9. 38 MHz • fits in a 130 x 55 cm enclosure Brian Sheehy February 17 -18, 2010

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

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

Pulse Shaping R&D ERL • 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 Brian Sheehy 8 February 17 -18, 2010

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

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

Beam shaping test using 532 nm Light A. Sharma, T. Tsang & T Rao PRSTAB 12, 033501 (2009) Brian Sheehy 11 R&D ERL February 17 -18, 2010

Beam shaping test using 532 nm Light A. Sharma, T. Tsang & T Rao PRSTAB 12, 033501 (2009) Autocorrelation signal Input pulse Cross-correlation signal Shaped pulse (de-convoluted) Brian Sheehy 12 R&D ERL Short/ long term stability February 17 -18, 2010

Diagnostics and Control R&D ERL • 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. Brian Sheehy 13 February 17 -18, 2010

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

Summary R&D ERL • 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) Brian Sheehy February 17 -18, 2010