Stabilization of the beam intensity for the high-resolution spectroscopy of iodine

An effective narrow-band controller based on a field programmable gate array (FPGA) is developed for the stabilization of a laser beam intensity in the megahertz range. Its principle is derived from the adaptive noise canceling techniques developed in the low-frequency region. The beam intensity is monitored by a photodiode which provides the error signal at the controller input. The canceling signal at the controller output drives the RF input power of an acousto-optic modulator (AOM) working in the linear part of its characteristic, which controls the beam intensity. The close loop system is equivalent to a notch filter tuned to a reference frequency applied to the controller. Some applications of this device in the field of high-resolution spectroscopy of iodine are presented.