Interferometers for studying small vibrations

Experimental methods for decreasing the mechanical noise level in interferometers used for detecting small vibrations are examined. The increase in the power of sources of coherent radiation has led to a situation in which the sensitivity of interferometers is, to a large extent, determined by mechanical fluctuations and not by the Poisson fluctuations in the light flux. Techniques have by now been developed that significantly decrease the level of mechanical noise. Similar techniques permit interferometers to be used in the presence of quite intense microseismic noise.