RUI: Modeling and Monitoring of Thermal Effects in Advanced LIGO

San Jose State University Foundation, San Jose CA

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). A sensor for monitoring of the curvature of the surface of an optic such as a mirror or beam-splitter will be developed using heterodyne measurements of the phase of a laser beam reflecting off the surface of the optic. The objective is to provide a method for in-situ monitoring of the curvature of a LIGO mirror that is capable of sensing the changes in shape of the surface to within 5%. Such changes occur when the instrument is in a transient state (such as when it is being turned on, aligned, or reset after environmental perturbations disturb it). The performance of the sensor will be investigated, optimized and calibrated in a table-top experiment with a small mirror that has its surface shape manipulated by localized heating induced by absorption of a second, higher power, laser beam. This work is important because it would allow the LIGO gravitational wave detectors to be better characterized during the "out-of-lock" time when the instruments (and the existing curvature sensors) are not operational, but when the mirror curvature changes (due to fluctuations in the power incident on the mirrors from the circulating laser beam affecting the thermal expansion of the mirror's substrate) are most rapid. By improving the characterization of the detector in its out-of-lock state, the time necessary to return it to the operational state can be reduced improving the duty cycle of the instrument, and hence its ability to observe astrophysically significant events. Because this project can be done as a table-top experiment, it will allow students to easily participate in the experiment and thus provide an important learning experience for both undergraduate and graduate students at San José State.