r&d erl laser and laser light transport
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
February 17-18, 2010
R&D ERL
Brian Sheehy
R&D ERLLaser 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
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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
Lambda (nm)
Laser Power
QE(CsK2Sb) max current
532 10 W ~1% 43 mA
355 5 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
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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 TEM00; M2 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/e2 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
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 .
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
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Laser Pulse Reptition Frequency 9.38 MHz Output Power
355 nm 5.5 W 532 nm 6.5 W
1064 nm 20 W Synchronization timing jitter 550 fsec (10Hz-1MHz) rms Pulse Length (532 nm) 8.2 psec Jitter in pulse length not measured Beam profile parameters, 355 nm
radius (1/e^2) 0.74 x 0.64 ellipticity 0.87
Beam profile parameters, 532 nm radius (1/e^2) 0.90 x 0.78
ellipticity 0.88 Beam profile parameters, 1064 nm
radius (1/e^2) 0.72 x 0.70 ellipticity 0.98
M2X 1.15 M2Y 1.1
Average output power stability at 355 nm < 1% rms Amplitude noise < 1% rms Centroid Position Stability Less than 3% of the beam radius (1/e2 level) Pointing Stability Less than 25 microradian contrast (355 nm) 3.E-06
February 17-18, 2010
R&D ERL
Brian Sheehy
7
February 17-18, 2010
R&D ERL
Brian Sheehy
Pulse Shaping
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• 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
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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
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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 LightA. Sharma, T. Tsang & T Rao PRSTAB 12, 033501 (2009)
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February 17-18, 2010
R&D ERL
Brian Sheehy
Beam shaping test using 532 nm LightA. Sharma, T. Tsang & T Rao PRSTAB 12, 033501 (2009)
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Autocorrelation signalInput pulse
Cross-correlation signalShaped pulse (de-convoluted)
Short/ long term stability
February 17-18, 2010
R&D ERL
Brian Sheehy
Diagnostics and Control
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• 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)