Noise of an acousto-optic modulator and limitations of an opto-electronic loop for laser beam intensity stabilization

摘要

The possibilities of beam intensity noise rejection offered by a narrow-band closed opto-electronic loop system are studied. The noise added to the beam by the acousto-opic modulator used as the actuator is computed. The intensity noise of the in-loop beam can be found below the standard quantum limit but the extracted beam noise is always above this limit. For an input beam with a small excess noise, an increase of the noise can be observed. A simple model of the loop based on the noise transfer functions approach is used for the calculation of the noise power of beam intensities and photocurrents. The behavior of the system and the limitations of noise rejection are analyzed.