SIDEBAND SPECTROSCOPY IN THE VISIBLE WITH A TUNABLE MODULATOR

Abstract

Phase modulation at microwave frequencies has been applied to the radiation of a cw ring dye laser in order to observe sideband spectra. In order to do this use was made of the electrooptic effect in a lithium tantalate bulk crystal. This spectroscopic technique allows relative frequencies to be determined instead of the more usual wavelengths. The design of the modulator allowed conservation of the phase matching condition (equality between light velocity and phase velocity of the microwave in the crystal) at microwave frequencies between 11 and 17 GHz. Sideband power of the order of 1 mW was produced. By scanning spectra simultaneously with two different sidebands and superimposing them on the same recording we were able to determine the frequency separation of hyperfine components of several iodine transitions. The distance between the $a_{1}$ component of the transition $P62 (17 - 1) of ^{127}I_{2}$ and the $b_{15}$ component of R66 (17 -1) [tentative assignment] was found to be $R66(17-1)b_{15}-P62(17-1)a_{1}=26164.6(43)MH_{z}.$