Baffle Material Characterization for Advanced LIGO by Cassandra

The transition to Advanced LIGO introduces new sensitivity requirements for the LIGO interferometers. When light scatters away from the main laser beam, then scatters off the beam tube and returns to the main beam, noise is introduced into the phase of the laser. The Auxiliary Optics Support subsystem uses baffles and beam dumps to control this scatter, but the baffle material and shape contribute some scatter as well. Careful selection of baffle material for Advanced LIGO is necessary in order to minimize baffle backscatter. Characterization of potential materials will also inform the geometry and placement of baffles. To this end, I developed a scatterometer experiment designed to measure the Bidirectional Reflectance Distribution Function (BRDF) of a material. The arrangement was used to measure the BRDF for black welder's glass, the prime candidate material for baffles in Advanced LIGO. I found that black glass has a BRDF on the order of 10, putting it within sensitivity requirements. Thesis Supervisor: Nergis Mavalvala Title: Professor Acknowledgments I owe a large debt of gratitude to Mike Zucker for supervising me on this project, for all his input, patience, and good humor. I would also like to thank Rich Mittleman for his role introducing me to LASTI and helping me find this project, as well as for good conversation about all things from LIGO to life. Thank you also to Nergis Mavalvala for agreeing to be my supervisor, and for all her help whipping this thesis into shape. My mom and dad, Laura and William Hunt, shaped my inquisitiveness and drive with their encouragement, and I appreciate their efforts to instill in me the value of hard work and scholarship. LIGO is funded by grants from the National Science Foundation.