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Slide1: 

Initial LIGO upgrade to 30 W: Implication for the Input Optics UFLIGO Group

Major IO components and concerns at 30 W: 

Major IO components and concerns at 30 W Electro-optic modulators Thermal lensing Degraded noise performance Long term damage? Mode cleaner Thermal lensing due to coating absorption MC_REFL beam  MC WFS How much of a problem? Coating hot spots? Faraday isolator Degraded isolation Thermal lensing  power dependent mode change into IFO Mode-matching telescope Probably no major concerns

Modulators I: 

Modulators I Current EOMs: New Focus LiNbO3 2 x 2 mm aperture Thermal lensing at 30W in LiNbO3 Absorption ~ 0.1-0.5% dnx/dT  dny/dT Need new EOMs!

Modulators II: 

Modulators II Advanced LIGO EOM development Nonlinear crystal: RTP and RTA 4 x 4 mm2 aperture Currently look at two EOM designs Hybrid UF/New Focus Home-made Summary of performance to date Bare crystals handle 95 W in 300 mm spots 400 hours of continuous testing Negligible thermal lensing RFAM reasonably good No worse than LIGO 1 Piezo-electric resonances in the 100s kHz regime Fluctuations correlate with pump power

Modulators II: 

Modulators II Hybrid UF/New Focus RTP ‘plug and play’ Pricy - $5500/EOM, but could negotiate bulk discount Home-made Materials are cheap, but manpower needed to assemble and test EOMs and spares costs $ Better temperature stability Not as well characterized, but should be within the next year

Mode Cleaner: 

Mode Cleaner Main issues Coating absorption Affects MC_REFL mode Impact on MC WFS 10X increase in intracavity power  10X increase in MC frequency noise Limiting noise source? Assumes current PSL RIN 10X increase in intracavity power  1.2 x 105 W/cm2 on each mirror Throughput Plagues current MCs w 0 curved mirror, MC2 flat RFPD mirror, MC1 flat mirror, MC3 Wavefront Sensors

Slide7: 

MELODY MODEL 3 W input, MC1 injection, 1.8 ppm coating loss

Slide8: 

30 W input, MC1 injection, 1.8 ppm coating loss

Slide9: 

30 W input, MC1 injection, no thermal lensing

Alternate MC geometry: 

Alternate MC geometry Inject beam into MC2 Lower AOI Requires some re-routing of beams in HAMs IOT table moves to HAM2 w 0 curved mirror, MC2 mirror, MC1 flat mirror, MC3 flat RFPD Wavefront Sensors

Slide11: 

30 W input, MC2 injection, 1.8 ppm coating loss

Mode Cleaner II: 

Mode Cleaner II 10X increase in input power  10X increase in MC frequency noise Limiting noise source? If so, is intensity stabilization able to handle this? 10X more power to PD Possible to live with higher df and reallocate problem to controls or elsewhere? Long term performance at higher power Are the MCs getting worse with time? Contamination? 10X increase in power  10X speed up in degradation? 100X? Current H1 MC has low throughput (65%) Scatterer on MC mirror? Serious negative implications for high power operation Change MC mirrors!

Faraday Isolator I: 

Faraday Isolator I FIs currently different in (H1, L1) and H2 H1, L1  initial FI, 10 mm aperture, 90% throughput, thermal beam drift on lock and unlock at low (2W) powers H2  new FI design, 20 mm aperture, low absorption TGG, 98% throughput, no beam drift, bench tested to 6W Advanced LIGO FI prototype tested Compensation of thermal birefringence and thermal lensing Predicted performance isolation > 40 dB at 100 W based on depolarization measurements Imperfect but reasonable thermal lensing compensation at 100 W Should be fine for 30W

Faraday Isolator II: 

Faraday Isolator II Current H2 FI Isolation at 30 W would be reduced relative to current performance How much?? Need to measure… Thermal lensing at 6 W negligible Evidence that calcite Brewster polarizers might lens at 30 W Worst case 25% loss of TEM00, mostly in focus change

Status of AdvLIGO Faraday Isolator : 

FR: Dual TGG crystal design + quartz compensator Thermal lens compensation KD*P –dn/dT material Isolation performance Status of AdvLIGO Faraday Isolator

Status of AdvLIGO Faraday Isolator : 

FR: Dual TGG crystal design + quartz compensator Thermal lens compensation K*DP –dn/dT material Isolation performance 31.5 dB Thermal Lens performance Status of AdvLIGO Faraday Isolator

Status of AdvLIGO Faraday Isolator : 

FR: Dual TGG crystal design + quartz compensator Thermal lens compensation KD*P –dn/dT material Isolation performance 31.5 dB Thermal Lens performance l/10 OPD across beam waist at 90 W single pass l/30 OPD expected at 30 W Negligible thermal lensing Status of AdvLIGO Faraday Isolator

Recommendations I: 

Recommendations I EOMs Need to be changed Impact mode matching into MC Simplest solution is to replace current EOMs with New Focus RTP version Could have a homemade one ready on a year time scale Mode cleaner High power operation problematic for REFL beam But is it really a problem? Need some investigations Solution is to inject through MC2 Major surgery, requires getting new mirrors and swapping

Recommendations II: 

Recommendations II Faraday Isolator Current H2 design *may* work Need to build another one and test it at 30 W AdvLIGO design prototype will work Costs: $50-60K for EOMs and spares $40K – 50K for FIs and spares $75K for new MC mirrors (do we need to do this?)

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