LIGO Scientific Collaboration Test Mass Down Select Meeting LIGO Scientific Collaboration

LIGO Scientific Collaboration Down Select Meeting Decision Date: June 30, 2004 Process More meetings (roughly monthly frequency) Recommendation to the LIGO Lab Directorate With a report to the LSC Today What do we know now? What do want to know (and can learn) by June 30? LIGO Scientific Collaboration

LIGO Scientific Collaboration Sapphire Absorption Lots of work on small pieces 30-50 ppm/cm 3 large pieces measured ~ 35 – 70 ppm/cm spread Factors of 2 inhomogeneity in sapphire problematic Annealing looks promising Need work on larger pieces Outstanding issues? Action items? LIGO Scientific Collaboration

LIGO Scientific Collaboration Thermal Compensation Necessary for both sapphire and fused silica Sapphire If absolute absorption < 20-30 ppm Inhomogeneities  spot heating needed fused silica More needed for absorption As noted before, coatings may require some compensation Prototyped and tested on initial LIGO and GEO Outstanding issues? Action items? LIGO Scientific Collaboration

Other Sapphire Parameters – OK or Close? LIGO Scientific Collaboration

LIGO Scientific Collaboration Fused Silica Bulk absorption good enough? Absolute value of < 1 ppm/cm Inhomogeneities up to few ppm/cm? Thermal Noise One large piece > 108 HWS program on annealing getting going Results by June? Outstanding issues? Action Items? LIGO Scientific Collaboration

Fused Silica Parameters – OK or Close? LIGO Scientific Collaboration

LIGO Scientific Collaboration Coatings I Thermal Noise: Choice of substrate dictates choice of coating Thermal and thermo-elastic noise impacts AdL strain However, titanium (bad actor) common to both sapphire and fused silica coatings Coating program to improve titanium, look at other coating materials TNI results Can get to sapphire? Outstanding Issues? Action items? LIGO Scientific Collaboration

LIGO Scientific Collaboration Coatings II Can’t forget about coating absorption AdL arm cavities suffer from changes in surface curvature due to high finesse + coating absorption Coating absorption inhomogeneities Large inhomogeneities force HR inhomogeneous thermal compensation Quiet CO2 laser  RIN < 10-6 rHz Limits Sapphire: 1 ppm on 1 ppm Fused silica: not nailed down (~2 ppm on 0.5 ppm?) Outstanding Issues? Action items? LIGO Scientific Collaboration

LIGO Scientific Collaboration Coatings III Measurements on surface scatter of LIGO I core optics Large point scatterers Imbedded in coatings (?) AdL Arm cavity loss budget tight  < 75 ppm Allocation to surface scatter  < 20 ppm Not met by current LIGO optics! Not clear how these issues differentiate between sapphire and fused silica Outstanding Issues? Action items? LIGO Scientific Collaboration

LIGO Scientific Collaboration Other Issues Future of sapphire vendors? We are a small part of Crystal Systems’ market GaN laser diode substrates primary market But, new GaN substrates demonstrated which may impact the sapphire market Impact on Crystal Systems business? And other sapphire vendors? Cost and Delivery impact Need updated information Attachment issues? Penultimate Mass considerations? Clear advantage for FS or sapphire? LIGO Scientific Collaboration

Charging and Patch Fields on TMs Charging identified as potential problem in AdL Not much known yet Putting Li into surface improves conductivity Effect on Q?? Equally possible for sapphire and fused silica? Outstanding issues? Action Items? LIGO Scientific Collaboration

What are the priorities in the next 3 months? Let’s decide here… LIGO Scientific Collaboration