Vacuum-ultraviolet frequency-modulation spectroscopy

Frequency-modulation (FM) spectroscopy has been extended to the vacuum-ultraviolet (VUV) range of the electromagnetic spectrum. Coherent VUV laser radiation is produced by resonance-enhanced sum-frequency mixing (nu(VUV) = 2 nu(UV) + nu(2)) in Kr and Xe using two near-Fourier-transform-limited laser pulses of frequencies nu(UV) and nu(2). Sidebands generated in the output of the second laser (nu(2)) using an electro-optical modulator operating at the frequency nu(mod) are directly transferred to the VUV and used to record FM spectra. Demodulation is demonstrated both at nu(mod) and 2 nu(mod). The main advantages of the method compared to VUV absorption spectroscopy are its background-free nature, the fact is that its implementation using table-top laser equipment is straightforward and that it can be used to record VUV absorption spectra of cold samples in skimmed supersonic beams simultaneously with laser induced- fluorescence and photoionization spectra. To illustrate these advantages, we present VUV FM spectra of Ar, Kr, and N-2 in selected regions between 105 000 cm(-1) and 122 000 cm-(1). Published by AIP Publishing.