Application of Squeezing to Gravitational Wave Detectors

The sensitivity of a gravitational wave detectors depends essentially on the stability and output power of the laser. In an improved version of the advanced LIGO detector called aLIGO the following laser system is used [1357]. 

Since their installation the aLIGO PSLs operate stable and provide reliable light sources for the gravitational wave detectors. 

In order to get an impression about the required characteristic data of a gravitational wave detector, in Table 9.1 the technical data of GEO 600 are compiled. 

The minimum detectable phase change A( is limited by the phase noise 8(pn. If the laser delivers N photons hv per second, the two detectors with quantum efficiencies of r] measure the intensities 

The noise power of both detectors adds quadratically. The signal-to-noise ratio for a detection bandwidth A/ 

The basic part of such a detector (Fig. 14.68) is a Michelson interferometer with long arms (several kilometers) and an extremely well stabilized laser. If a gravitational wave causes a length difference AL between the two arms of the interferometer, a phase difference A0 = (47t/A,) AL appears between the two partial waves at the exit of the interferometer. The minimum detectable phase change A0 is limited by the phase noise If laser delivers N photons hv per second, the two detectors measure the intensities 

In Sect. 14.8.1 it was shown that the noise limit without squeezing is caused by the zero-point field coupled into the second input part of the interferometer. If a beam of squeezed light is fed into this input part, the noise level can be decreased and the detectable length change AL can be further decreased [14.166]. 

For a more detailed representation of squeezing, the most recent experiments on the realization of squeezing, and for further applications of this interesting technique, the reader is referred to the literature [14.169-14.175]. 

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