An RUI Proposal to Study Thermal Noise and Bilinear Noise in LIGO and Advanced LIGO

Hobart And William Smith Colleges, Geneva NY

Investigators

Abstract

This award supports research to overcome noise sources that are expected to limit the sensitivity of Advanced LIGO. The high-index of refraction coating material to be used initially in Advanced LIGO is the main source of thermal noise. Past research to determined the source of excess loss in a low-index coating material allowed demonstration of how it may be reduced or eliminated. These studies of low-index material provided important indicators to guide the search for the necessary high-index coating but with low mechanical loss. LIGO scientists have studied and reduced the multitude of sources of noise that directly couple into the interferometer, thereby exposing indirect, bilinear noise processes, such as up-conversion of noise produced outside LIGO's band of sensitive frequencies into that band. Bicoherence provides a measure of such bilinear coupling while being insensitive to Gaussian noise. Development of a data monitor for bicoherence will continue under this award. Once identified, this noise can be monitored and if possible, eliminated. The bicoherence calculation engine could be adapted eventually to search for gravitational waves, since inspiral and burst signals both have nonzero bicoherence. Advanced LIGO, which is scheduled to be fully operational by 2015, has been designed with a sensitivity to allow it to make regular observations of gravitational waves. Improvement in Advanced LIGO sensitivity through improved optical coatings and amelioration of up-conversion noise will allow achievement of the greatest discovery potential. The PI plans to involve several undergraduates in his research. This matches well with Hobart and William Smith 9HWS0 Colleges' ongoing effort to expand their science program. The opportunity to work in research programs like LIGO at HWS is helping to increase the number of physics majors and to change their attitude about a career in physics.