Lasers or Advanced Intererometers Benno Willke Aspen Meeting Aspen CO, February 2004 G040041-00-Z
Requirements - Topology Sagnac: broadband source to reduce scattered light noise power control recycled Michelson: coherence control power control spatial control squeezed light IFOs power control dierent wavelength Prestabilized Laser System (PSL)
Design Requirements stability / reliability sot ailure mode easy to maintain / rare maintenance interval good eiciency good stationarity / low glitch rate high bandwidth / large range actuators
Laser Design common concept: laser diode pumped solid state lasers transer requency stability o low power master laser to high power stage Maser Laser Power Ampliier (MOPA) injection locked oscillator dierent power stage concepts: rods zig-zag slabs ibers thin disc lasers / active mirror laser
Nd:YAG Master-Laser NPRO (non-planar ring oscillator) output power: 800mW requency noise: [ 10kHz/ ] Hz/sqrt(Hz) power noise: 10-6 /sqrt(hz)
High Power Stage main problem: thermal design stress racture thermal lensing spatial proile bireringence with tangential and radial principle axis solutions reduce deposited heat Yb:YAG, high eiciency propagate beam perpendicular to temperature gradient zig-zag, thin disc lasers increase interaction length iber lasers compensate bireringence
Face-pumping - Edge-pumping zig-zag slab Pumping Cooling zig-zag plane Facepumping Edgepumping Pumping Cooling zig-zag plane Stanord High Power Laser Lab Adelaide University ity
End pumped slab geometry undoped end 808nm Pump signal IN 1.51cm 3.33cm 1.51cm undoped end 0.6% Nd:YAG signal OUT 808nm Pump 1.1mm X 0.9mm Stanord High Power Laser Lab
Stanord High Power Concept 10W LIGO MOPA System ISOL ATOR Mode-matching optics 20 W Ampliier TO PRE MODE CLEANER Lightwave Electronics 2-pass End Pumped Slab #2 Pump Power = 430 W Expected TEM 00 Output Power = 160W Pump Power = 130 Output TEM 00 Power = 50 W 2-pass End Pumped Slab #1 Mode-matching optics
End Pumped Rods Nd:YAG - GEO600 Laser (14W) Nd:YVO 4 - Virgo Laser (20W) Laser Zentrum Hannover
20% OC 801 5050 20% OC Q R 2 iber bundle 10 X30W Q Rrelayop tics 801 5050 2 iber bundle 10 X30W relayop tics HR HR B rewster Plate B rewster Plate 54 mlas erod wit htwou ndoped endca ps 54 mlas erod wit htwou ndoped endca ps LZH High Power Concept QR output BP rom Master QR HR@1064 HT@808 2
Fiber Lasers Pump light A ctive iber Laser radiation HR-m irror Coupling optics Outcoupler Collimator Laser radiation Pump light Outer ladding Active core Inner cladding = pump core courtesy H. Zellmer
Fiber Laser Result o Jena Group NPRO Backscattered signal Isolator 9.4 m Yb-doped LMA-iber Dichr. mirror Fiber coupled laser diode Input-output diagram To experiment Output power [W] 120 100 80 60 40 Backscattered signal [a.u.] 8 6 4 2 0 0 20 40 60 80 100 120 Output power [W] 20 Opt. eiciency = 70% 0 0 20 40 60 80 100 120 140 160 180 Launched power [W] Yb-doped LMA-Fiber Core: = 28.5 µm, NA = 0.06 MFD 23 µm Doping. 700 ppm (mol) Yb 2 O 3 Pumpc.: = 400 µm, NA = 0.38, D-Form Seed: 800 mw Diraction limited (M 2 = 1.1) Polarization 82% (10:1)
Modeling/Overview pump light distribution ray tracing analytical approximation experimental data heat generation gain wave propagation through inhomogenous medium Finite Element Method or calculating temperature distribution mechanical stress deormation cooling calculation o optical properties inite dierencing split step ourier approach k-vector thermal lens stress-induced bireringence
Advanced LIGO Laser Requirements Power / Beamproile: 165W in gausian TEM 00 mode less than 5W in non- TEM 00 modes Drit: 1% power drit over 24hr. 2% pointing drit Control: tidal requency acuator +/- 50 MHz, time constant < 30min power actuator 10kHz BW, +/-1% range requency actuatot BW:<20 o lag at 100kHz, range: DC-1Hz: 1MHz, 1Hz-100kHz: 10kHz
Injection Locked Oscillators - Hannover QR output NPRO FI EOM BP FI HR@1064 HT@808 QR 2 YAG / Nd:YAG / YAG 3x 7x40x7 modemaching optics BP YAG / Nd:YAG 3x2x6 High Power Slave 20 W Master key elements: undoped bonded end-caps bireringence compensation pumplight homogenization
Prestabilized Laser PSL requency stability: stabilize master laser to rigid or suspended-mirror cavity power stability: eed-back to pump source o high power stage passive iltering at r spatial proile passiver modecleaning active mode compesation
requency noise requirement
intensity noise requirement
Adv LIGO - PSL optical layout high power ring laser 200W GEO typ ring laser 15W NPRO 1W spatial ilter resonator (PMC) requency reerence resonator AOM
PSL stabilization scheme intensity stabilization outer loop injection locking intensity stabilization inner loop PMC loop requency stabilization inner loop requency stabilization outer loop
Power Noise Reduction
High Power Slave 87 W output power linear polarized single transverse mode M 2 x,y ~ 1,2 PD PD λ/2 FI CCD PD PMC Modemaching PD Output beam λ/4 λ/2 λ/2 MISER EOM FI
Relock Time 2 1 0 Piezo Ramp: Master 1,3 Hz (770ms) Slave 2.5 Hz (400ms) Slave 12 W Master -1 PD Signal [V] -2-3 -4-5 -6-7 -8-0,4-0,3-0,2-0,1 0,0 0,1 0,2 0,3 0,4 t [s] relock time < 500 ms aster relock possible depending on piezo ramp
Bireringence Compensation
20% OC 801 5050 20% OC Q R 2 iber bundle 10 X30W Q Rrelayop tics 801 5050 2 iber bundle 10 X30W relayop tics HR HR B rewster Plate B rewster Plate 54 mlas erod wit htwou ndoped endca ps 54 mlas erod wit htwou ndoped endca ps End-Pumped Rods QR output BP rom Master QR HR@1064 HT@808 2
Summary dierent high power stages: - end-pumped slabs - end-pumped rods - iber ampliier dierent topologies: - MOPA - injection locking Advanced LIGO pre-stabilized laser system status o laser development possible stabilization schemes
high power stage status Feb 2004 250 200 no re-alignment re-optimized @ 40A linear polarized with bireringence compensation output power [W] 150 100 50 0 20 25 30 35 40 45 Diode current