Tunable-diode-laser frequency-modulation spectroscopy using balanced homodyne detection

Abstract

Quantum-limited frequency-modulation spectroscopy (FMS) has been performed with tunable diode lasers at 5.4 and 1.3 microm by employing a dual-beam balanced homodyne detection scheme to suppress optical fringes, residual amplitude modulation, and excess laser noise by 15-20 dB. Performing FMS at the two wavelengths involved different lasers (lead salt and InGaAsP, respectively), optics, and detectors, which emphasizes the versatility and applicability of the technique. System sensitivities of 1 x 10(-7) and 2 x 10(-7) were obtained for the respective systems.