Laguerre-Gauss Beams for Test Mass Thermal Noise Reduction

Abstract

Test mass thermal noise was not a dominant noise source in the first generation of gravitational wave detectors. However, with the upgrade to second generation detectors, a factor of 10 increase in sensitivity in the whole frequency band is aimed for, and at such improved sensitivities thermal noise is expected to be one of the major limiting noise sources. The Brownian thermal noise in particular is expected to be of sufficient magnitude to obscure gravitational wave signals around the 100 Hz region in the advanced detectors, unless new techniques are employed to reduce the effect. This point is illustrated in the projected sensitivity of the Advanced LIGO detector, shown in Fig. 2.1. From the second generation onwards therefore, advancements in other areas of the interferometers, such as the implementation of higher laser powers, will make a limited impact in the 100 Hz region unless the thermal noise of the test masses can be reduced. Research into methods for reducing the effects of this noise source is therefore of paramount importance to the gravitational wave community.