FM spectroscopy of monodeuterated methane as a frequency standard at 1.54 μm

Frequency-modulation spectroscopy of the CH₃D molecule is performed to assess a novel optical frequency standard at 1.54-μm wavelength. Numerical integration of the demodulated first derivative signals provides the Voigt absorption profiles for the R(6,3) transition at 1543.78 nm at different gas pressures. Deconvolution with the Gaussian (Doppler) line provides the corresponding Lorentzian (collisional) line as a function of the gas pressure. Measurements of the collisional broadening contribution, at three different gas pressures, provide a collisional broadening coefficient of 37 MHz/kPa for the R(6,3) line.