On the Conrol Aspect of Laser Frequency Stabilization

The realization of frequency-stable lasers is viewed as a key to progress in many areas of research, so the search for more effective techniques of frequency stabilization has intensified significantly in recent years. NASA\´s "SUNLITE" project at Langley Research Center is investigating and validating the fundamental linewidth and frequency stability limits of a Nd:YAG laser oscillator locked to a high finesse reference cavity in the microgravity and vibration-free environment of space. As part of this project, NASA engineers have designed and built a space-qualified system for measuring the linewidth and stability limits of an ultra-stable laser oscillator in space. In order to achieve greater stability and better performance, both passive and active frequency control, which requires use of a feedback control loop, has been applied. By using this technique of frequency stabilization, which is based on the fundamental property of feedback control theory, the intrinsic frequency noise and drift of the laser are expected to be reduced to the measurement noise level. The objetive of this paper is to further investigate the application of feedback control theory in active frequency control as a frequency stabilization technique and determine the most appropriate control strategy to be used, particularly in the SUNLITE project.