| The light emitted from any real laser fluctuates in amplitude. This fluctuation, called laser amplitude noise, can degrade the signal-to-noise ratio of interferometers. The Laser Interferometer Gravitational-Wave Observatory (LIGO) proposes to use an interferometer to measure very small strains produced by gravitational waves. Reducing laser-amplitude noise, particularly in the dc to kHz frequency range where the signal is expected, is required if LIGO is to be successful.; Two techniques are commonly employed for reducing laser-amplitude noise. Passive cavity filtering reduces amplitude fluctuations, but only at frequencies above the cavity linewidth. Electronic feedback has been successfully employed to provide reduction, particularly of the resonant relaxation oscillations of diode-pumped solid state lasers, but is limited by shot noise introduced by the feedback photodetector.; We present the pump and signal resonant optical parametric oscillator (OPO) as another means of suppressing laser-amplitude noise. We show that the interaction between the two resonant fields transfers amplitude fluctuations from the pump beam to the signal beam. With such a device, we have observed 35dB/Hz reduction in the relative intensity noise of a 750mW non-planar ring oscillator (NPRO) from dc to kHz frequencies. We also show that suppression can occur up to MHz frequencies and that the frequency range of the suppression is determined by the input power to the OPO. |
