Ultra-stable, high-power laser systems

Patrick Kweeon behalf of AEI Hannover and LZH

Advanced detectors session, 26. March 2011

Albert-Einstein-InstitutHannover

22

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

Current Laser Systems

44

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

55

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

66

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

77

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

88

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

99

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

1010

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

Third generation

λ=?1kW

1212

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]

1313

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

1414

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

1515

Summary

Patrick Kwee

• Laser system of Advanced LIGO

• Power scaling

• Stabilization methods

• Developments for

third generation

Ultra-stable, high-power laser systems

1616

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

1717

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