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R&D ERL Laser and laser light transport

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

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R&D ERL Laser and laser light transport

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

  2. Laser and Laser Light Transport • Laser Requirements • System Description • Master Oscillator Power Amplifier • Temporal Shaping • Spatial Shaping • Transport • Diagnostics & Controls

  3. Laser Requirements Rep Rate: 9.38 MHz, phase locked with 75th harmonic, the 703.5 MHz RF frequency of the superconducting cavities. Jitter < 1psec rms Wavelength: tradeoff between ease of production/shaping and attainable QE   Temporal Shape: 50 psec flat top, 10 psec rise Spatial Shape: Flat top, 1e-6 pedestal 3

  4. Laser Specifications The stability, rep-rate and power requirements motivated the choice of a master oscillator – power amplifier (MOPA) configuration based on Nd:YVO4 (1064 nm), with subsequent frequency multiplication . 4

  5. 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

  6. Laser Performance Summary 6

  7. 7

  8. Pulse Shaping • 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 8

  9. Pulse Stacking for Temporal Shaping R&D ERL Interferometric Method Birefringent Method Tomizawa et al Quant Elec 2007 Sharma et al PRSTAB 2009 • 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 • derive fast pulse from dump light 9

  10. Spatial Shaping • Commercially available, Gallilean telescope using aspheric lenses so that the magnification is radially dependent. • Flat top to 5% • very sensitive to input pulse parameters 10

  11. Beam shaping test using 532 nm LightA. Sharma, T. Tsang & T Rao PRSTAB 12, 033501 (2009) 11

  12. Beam shaping test using 532 nm LightA. Sharma, T. Tsang & T Rao PRSTAB 12, 033501 (2009) Cross-correlation signal Shaped pulse (de-convoluted) Autocorrelation signal Input pulse Short/ long term stability 12

  13. Diagnostics and Control • 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. 13

  14. System Overview

  15. 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)

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