The Behavior of Laser Modes in a Medium with Time Varying Dielectric Constant.

The effect, on semiconductor laser modes, of a time-varying modulation of the complex dielectric constant of the active region of the laser, is considered. It is seen that the main effect is to produce frequency modulation associated with modulation of the real part of the dielectric constant while modulation of the imaginary part gives rise to amplitude modulation. Two methods for producing the modulation are considered. The first, pressure via ultrasonic waves, produces pure frequency modulation in impure material. The second, modulation of the injection, results in both amplitude and frequency modulation. Experiments to confirm this analysis were carried out on a cw GaAs injection laser. The modulated laser spectrum was observed with a Fabry-Perot Interferometer. High resolution measurements on the pulsed spectral shift of a GaAs laser at 77K and 4.2K were performed using a Fabry-Perot interferometer. The feasibility of detecting modulation on a pulsed semiconductor laser was demonstrated. Author