SIDE-BAND SPECTROSCOPY IN THE VISIBLE WITH A TUNABLE MODULATOR

Phase modulation at microwave frequencies has been applied to the radi ation of a cw (continuous wave) ring dye laser to observe side-band sp ectra. To do this, use was made of the electro-optic effect in a lithi um tantalate bulk crystal. This spectroscopic technique allows relativ e frequencies to be determined instead of the more usual wavelengths. By scanning spectra simultaneously with two different side bands and s uperimposing them on the same recording, we were able to determine the frequency separation of hyperfine components for several iodine trans itions. 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. Side-band power of the order of 1 mW was produced. We demo nstrate the application of this spectroscopic technique to iodine. Exa mples of spectra around 576 and 633 nm are given. Further application of this source (e.g., double-resonance experiments, frequency standard s) is discussed.