Stark-modulation-enhanced FM-spectroscopy

Diode lasers are a versatile tool for fundamental atomic and molecular spectroscopy and have increasing applications in gas analysis and diagnostics. In order to obtain quantum limited performance, the problem of the suppression of time-dependent unwanted background structures superimposed to the desired signal from the spectral feature under investigation has to be addressed. Sample modulation enhanced FM-spectroscopy as described in this paper combines laser frequency modulation (FM) with a sample modulation, based on the Stark effect in molecular spectra. The transitions 1(10) - 1(11) at 1746.2 cm(exp -1) and 5(33) - 4(32) at 1759.9 cm(exp -1) in the v2-band of H2CO have been used in experiments with static and AC electric fields up to 2 kV cm(exp -1). An intercomparison of the FM technique and the FM-Stark double modulation scheme demonstrates the remarkable potential of this technique for background suppression.