DEVELOPMENT OF A LINE-NARROWED AND FREQUENCY-STABILIZED TDL SYSTEM FOR SUB-DOPPLER MOLECULAR-SPECTROSCOPY

The spectral resolution of TDL spectrometers is generally limited by t he finite spectral width of the TDL radiation. Usually, the spectral p urity of lead-salt diode lasers is sufficient to perform Doppler-limit ed studies but is inadequate to resolve sub-Doppler spectroscopic feat ures like saturated-absorption signals. The application of external op tical feedback allowed us to reduce the linewidth of tunable diode las ers by two orders of magnitude down to 200 kHz. In a frequency-offset locking scheme we stabilized and controlled the frequency of the narro wed line. This technique enabled us to use the TDL as saturating and p robing laser in a saturation experiment: we observed a nonlinear absor ption signal (Lamb dip) in an OCS absorption line with very high resol ution. The current performance of our TDL system is reported and the r esolution and accuracy limits are discussed.