Laser noise control in the optoacoustical gravitational antenna

Abstract

It is shown that the metric sensitivity theory of the OGRAN project contains description of the Fabry-Perot cavity displacement readout scheme proposed by Braginsky. In theories a quality factor defines laser noise. As an alternative, two phenomenological intrinsic controlled parameters of laser noise are proposed to analyze readout resolution: spectral densities of frequency deviations and power random modulation P(t) = P 0[1 + £(t)]. The formula for vibration noise is derived. The new theory of instrumental sensitivity is applied to explain the effect of readout noise rise while increasing digitization time. To reduce the readout threshold signal from real value of 2 · 10−15 cm/Hz1/2 to required value of 3 · 10−16 cm/Hz1/2 there are proposed actions: 1) to limit temperature drift difference between laser and bar cavity frequencies by value of 250 Hz; 2) to suppress by circuitry means vibration disturbance voltage at the discriminator output while increasing by 20 dB width of feedback frequency range and feedback gain in this range.