SPECTROSCOPIC APPLICATIONS AND FREQUENCY LOCKING OF THZ PHOTOMIXING WITH DISTRIBUTED-BRAGG-REFLECTOR DIODE-LASERS IN LOW-TEMPERATURE-GROWN GAAS

A compact, narrow-linewidth, tunable source of THz radiation has been developed for spectroscopy and other high-resolution applications. Dis tributed-Bragg-reflector (DBR) diode lasers at 850 nm are used to pump a low-temperature-grown GaAs photomixer. Resonant optical feedback is employed to stabilize the center frequencies and narrow the linewidth s of the DBR lasers. The heterodyne linewidth full-width at half-maxim um of two optically locked DBR lasers is 50 kHz on the 20 ms time scal e and 2 MHz over 10 s; free-running DBR lasers have linewidths of 40 a nd 90 MHz on such time scales. This instrument has been used to obtain rotational spectra of acetonitrile (CH3CN) at 313 GHz. Detection limi ts of 1x10(-4)Hz(1/2) (noise/total power) have been achieved, with the noise floor dominated by the detector's noise equivalent power. (C) 1 997 American Institute of Physics.