STABILIZATION OF A MULTIMODE HE-NE-LASER - A VIVID DEMONSTRATION OF THERMAL FEEDBACK

A thermal stabilization technique for multimode He-Ne laser tubes is d emonstrated. Intensity stability of approximately 1% is achieved, wher e the intensity of the unstabilized laser varied by more than a factor of 5. The system provides both a dramatic demonstration of the princi ple of negative feedback and a stimulating introduction to basic elect ronics, laser physics, and solid state physics. It is simple enough to be constructed as an undergraduate laboratory project.