Abstract

We recently developed a novel scheme¹ to overcome the residual amplitude modulation (RAM) background of frequency modulation spectroscopy.² This technique calls for a specially designed laser phase modulator with high response at one rf frequency and modest response at the harmonic of that frequency. To that end, we have modified the usual modulator design by fabricating an inductively loaded device with resonant response adjustable from ~150 to 350 MHz depending on the size of the inductor. At the highest resonance frequency, we observed a modulation index enhancement of as much as 80% over that obtained with an unloaded modulator. We report here the results of extensive computer modeling and experimental characterization of the new device. The model contains a resonator formed by an external inductor in parallel with the electrooptic crystal. The parasitic effects of the microstrip are represented by additional series inductance and parallel capacitance. Agreement between the model and experiment is quite satisfactory.

© 1989 Optical Society of America