5 Laser Interferometric Techniques for Gravitational-Wave Detectors

As explained in Section 4.4.1, high-power laser light is needed to overcome limitations of a detector’s sensitivity due to photoelectron shot noise. The situation can be helped greatly if a multi-pass arrangement is used in the arms of the interferometer as this multiplies up the apparent movement by the number of bounces the light makes in the arms. The multiple beams can either be separate, as in an optical delay line [313, 95], or may lie on top of each other as in a Fabry–Pérot resonant cavity [129], as shown in Figure 9View Image.

View Image

Figure 9: Michelson interferometers with (a) delay lines and (b) Fabry–Pérot cavities in the arms of the interferometer.

Optimally, the light should be stored for a time comparable to the characteristic timescale of the signal. Thus, if signals of characteristic timescale 1 msec are to be searched for, the number of bounces should be approximately 50 for an arm length of 3 km. With 50 bounces the required laser power is reduced to 2.4 × 103 W, still a formidable requirement.

 5.1 Power recycling
 5.2 Signal recycling
 5.3 Application of these techniques
  5.3.1 Technical noise requirements
  5.3.2 Laser design
  5.3.3 Thermal compensation and parametric instabilities
 5.4 Readout schemes

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