High-resolution fast terahertz time-domain gas spectroscopy based on a fine comb spectral structure of the NovoFEL

High coherency and monochromaticity of the terahertz Novosibirsk Free-Electron Laser (NovoFEL) is appeared in very narrow comp spectral structure of its radiation (relative linefs width is 2·10
^-8
, interval between lines is 5.6 MHz, total width of the comb-structure is 6-12 GHz). Sampling time-domain spectroscopy with resolution of order of the line width (≈ 100 kHz) needs measuring time about of 20 μsec per one sampling point and only 56 slow sampling points to overlap the full NovoFEL comb spectrum. Shift of the comb structure will be made by changing of length of the NovoFEL optical resonator. Universal terahertz gas laser (line width. ≤ 0.5·10
^-8
) will be used as local oscillator in the heterodyne spectrometer.