GENERATION OF MULTIFREQUENCY LASER-EMISSION USING AN ACTIVE FREQUENCY SHIFTED FEEDBACK CAVITY

A dye laser possessing frequency shifted feedback is employed to create a wide spectrum of discrete, narrowly spaced frequency components. A monochromatic signal injected at a particular frequency, is shifted up by a fixed frequency interval on each round trip using an intra-cavity acousto-optic modulator (AOM). The gain in the laser compensates for the loss and permits the signal to circulate in the resonator several hundred times, leading to spectra extending over tens of gigahertz. In the present case, the AOM frequency, and thus the frequency spacing of the components, is 80 MHz. Moreover, since the light is shifted away from the frequency of injection, it is possible to create spectra with extremely sharp edges but otherwise essentially broadband. Calculations using a rate equation model are in semi-quantitative agreement with the observed results.