Two-channel opto-acoustic diode laser spectrometer and fine structure of methane absorption spectra in 6070-6180 cm-1 region

We describe the hardware and software of the high-sensitive two-channel opto-acoustic spectrometer with a near infrared diode laser. A semiconductor TEC-100 laser with outer resonator generates a continuous single-frequency radiation in the range of 6040-6300 cm(-1) with spectral resolution better that 10 MHz. The newly designed model of photo-acoustic cells in the form of a ring type resonator was used in the spectrometer, and the system allows the measurement of a weak absorption coefficient equal to 1.4 x 10(-7) cm(-1) Hz(-1/2) with a laser radiation power of 0.003 W. The methane absorption spectra within a range of 6080-6180 cm(-1) were measured with a spectral resolution of 10 MHz and the signal to noise ratio more than 10(3). Six hundred absorption lines were recorded, which is twice as many as in HITRAN-2004. The accurate measurements of the half-width and shift of methane unresolved triplet R-3 of 2 nu(3) band permit us to determine values of the broadening and shift coefficients for CH4-air, CH4-N-2, and CH4-SF6 Mixtures. (c) 2006 Elsevier B.V. All rights reserved.