ultra-stable, high-power laser systems patrick kwee on behalf of aei hannover and lzh advanced...
DESCRIPTION
Current Laser SystemsTRANSCRIPT
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Ultra-stable, high-power laser systems
Patrick Kweeon behalf of AEI Hannover and LZH
Advanced detectors session, 26. March 2011
Albert-Einstein-InstitutHannover
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Motivation
Laser noise couples to GW read out channel
Ultra-stable, high-power laser systemsPatrick Kwee
Reduce coupling• Null instrument, ... • Exploiting symmetries, ...
Reduce noise• High laser power → reduces quantum noise• Ultra stable laser → reduces technical noise
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Current Laser Systems
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NPRO
Patrick Kwee
• Non-planar ring oscillator (NPRO)
• Solid state Nd:YAG laser, 1064nm
• Diode pumped at 808nm
Perfect laser for GWD ...
• Exceptional frequency stability
• Low power noise, low pointing noise
• Good beam quality
• ... but too low output power (max. ~2W)
[Kane, Byer, "Monolithic, unidirectional…" Opt. Lett. 10, 65-67 (1985)]
Ultra-stable, high-power laser systems
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Laser Power & Quantum Noise
Patrick Kwee
• First generation used ~10W
• Second generation ~100W
• Third generation asks for ~1kW
shot noise
radiation pressure noise
higher laser power
Ultra-stable, high-power laser systems
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Power Scaling to 200W
Patrick Kwee
• Single pass Nd:YVO amplifier, 35W,
used at eLIGO, GEO HF
• Nd:YAG ring oscillator, 200W,
injection locked, depolarization
compensated, used at aLIGO
[Winkelmann et al., App. Phys. B, 102:529-538, 2011]
Ultra-stable, high-power laser systems
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Laser Stabilization
Patrick Kwee
[Kwee, ”Laser characterization and stabilization for…”, Ph.D. thesis (2010)]
• Active stabilization• Sensors• Actuators• Feedback control loops
• Passive filtering• Optical resonators• Birefringent crystals• ...
Ultra-stable, high-power laser systems
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Beam Quality
• Laser power required in fundamental mode of IF, TEM00
• Higher order modes cause additional shot noise and noise couplings
• Rigid spacer ring cavity (called PMC)• Transmits only TEM00 mode
• TEM00 fraction increased from ~95% to >99%
Patrick Kwee Ultra-stable, high-power laser systems
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Power Noise
Patrick Kwee
• Coupling via radiation pressure and dark fringe offset between ~10Hz ... ~10kHz
• Active pre-stabilization, photodetector as sensor,
AOM as actuator
Ultra-stable, high-power laser systems
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Frequency Noise
Patrick Kwee
• High frequency stability required for interferometer lock acquisition
• Active pre-stabilization, rigid reference resonator as sensor, several high-bandwidth actuators
Ultra-stable, high-power laser systems
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Third generation
λ=?1kW
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Many Options…
More power, kW class• Interesting for high-frequency sensitivity• All reflective interferometers could handle higher powers
Different wavelength• Longer wavelength (1550nm) for silicon optics, cryogenic
interferometers
Spatial beam profile• Lag33 mode• Flat-top profiles
Patrick Kwee Ultra-stable, high-power laser systems
[LIGO DCC T1000416]
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Current Developments
• 1kW @ 1064nm – 2W NPRO as seed– photonic crystal fiber amplifier for ~500W regime (current record
is ~500W, but military research)– Subsequent single-pass Nd:YAG amplifier for ~1kW– Coherent beam combining for ~1kW
• 100W @ 1550nm– 1-2W DFB fiber laser as seed– Erbium fiber amplifier for ~100W (currently ~50-60W)
• 100W @ 532nm– 200W @ 1064nm solid-state laser system – High-power frequency doubling with LBO (currently ~130W)
Patrick Kwee Ultra-stable, high-power laser systems
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Stabilization
• Frequency pre-stabilization ✓ (only necessary for lock acquisition)• Beam quality ✓ (rigid filter resonators work fine)• Power noise at radio frequencies ✓ (filter resonators could be cascaded)
• Beam pointing (✓) (only passive until now, active stabilization possible)• Power stabilization (✓) (already limited, but new concepts on hand)
Patrick Kwee Ultra-stable, high-power laser systems
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Summary
Patrick Kwee
• Laser system of Advanced LIGO
• Power scaling
• Stabilization methods
• Developments for
third generation
Ultra-stable, high-power laser systems
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Power Noise at RF
• Coupling via interferometer heterodyne readout, alignment readout, …• Modulation frequencies between 10MHz...100MHz
• Rigid spacer ring cavity
acts as low-pass filter
Patrick Kwee Ultra-stable, high-power laser systems
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Fiber Amplifers
• Substantial progress in recent years• Very good intrinsic beam quality• Very compact laser systems• High effiency• All-fiber systems possible
But...• Same reliability as solid-state systems?• Non-linear effects due to high intensities• Sensitive to acoustics
Patrick Kwee Ultra-stable, high-power laser systems