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Ultra-stable, high-power laser systems

Ultra-stable, high-power laser systems. Patrick Kwee on behalf of AEI Hannover and LZH Advanced detectors session, 26. March 2011. Albert-Einstein-Institut Hannover. Motivation. Laser noise couples to GW read out channel. Reduce coupling Null instrument, ...

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Ultra-stable, high-power laser systems

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  1. Ultra-stable, high-power laser systems Patrick Kwee on behalf of AEI Hannover and LZH Advanced detectors session, 26. March 2011 Albert-Einstein-Institut Hannover

  2. Motivation Laser noise couples to GW read out channel • Reduce coupling • Null instrument, ... • Exploiting symmetries, ... • Reduce noise • High laser power → reduces quantum noise • Ultra stable laser → reduces technical noise Ultra-stable, high-power laser systems

  3. Current Laser Systems

  4. NPRO • 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

  5. Laser Power & Quantum Noise radiation pressure noise shot noise higher laser power • First generation used ~10W • Second generation ~100W • Third generation asks for ~1kW Ultra-stable, high-power laser systems

  6. Power Scaling to 200W • 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

  7. Laser Stabilization • Passive filtering • Optical resonators • Birefringent crystals • ... • Active stabilization • Sensors • Actuators • Feedback control loops [Kwee, ”Laser characterization and stabilization for…”, Ph.D. thesis (2010)] Ultra-stable, high-power laser systems

  8. 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% Ultra-stable, high-power laser systems

  9. Power Noise • 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

  10. Frequency Noise • 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

  11. Third generation λ=? 1kW

  12. 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 [LIGO DCC T1000416] Ultra-stable, high-power laser systems

  13. 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) Ultra-stable, high-power laser systems

  14. 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) Ultra-stable, high-power laser systems

  15. Summary • Laser system of Advanced LIGO • Power scaling • Stabilization methods • Developments for • third generation Ultra-stable, high-power laser systems

  16. 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 Ultra-stable, high-power laser systems

  17. 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 Ultra-stable, high-power laser systems

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