High-sensitivity FM spectroscopy with a lead-salt diode laser

Abstract

We report the demonstration of near-quantum-noise-limited sensitivity with a lead-salt diode laser using FM spectroscopy and high-speed sweep integration. Using both single-tone and two-tone techniques, we demonstrated an absorption sensitivity of ~2 x 10(-7) in a 2.44-Hz bandwidth from a Doppler-broadened NO line at 1856.5 cm(-1). The sensitivity in our experiments was limited by laser excess noise, which was about four times the expected quantum-noise level.