Two studies using a tunable diode laser with frequency controlled by a stepping Michelson interferometer

The interference pattern obtained from a tunable diode laser beam through a stepping Michelson interferometer allows active control of its emission frequency. Two illustrations are given: (a) the N2O concentration (approximate to 100 ppbv) in stratospheric air samples has been measured with a precision of 3%. (b) the R(23) line of the CO fundamental band is analysed from a very low pressure of pure gas to pressures of about 1 atm in a CO-Xe gas mixture. Doppler, Dicke confinement and speed-dependent collision broadening effects act successively when the gas pressure increases. The narrowing parameter obtained by fitting the hard collision model (Rautian Sobel'man profile) to the observed line at pressures less than or equal to 40 Torr gives a value of the diffusion coefficient close to the value deduced from the transport properties of gas mixtures.