Second Derivative Tunable Diode Laser Spectrometry for Line Profile Determination. II. Experimental Results

The effect of the amplitude of the current modulation on experimental second derivative spectra measured using a tunable diode laser spectrometer is discussed. Spectra with adequate signal/noise ratios can only be measured when the amplitude of the modulation is about equal to the half width at half height. Two parameters, the distance between the zero crossings and the ratio of the minimal and maximal excursions, may be fit to an empirical hypersurface to obtain values for the peak absorbance, the actual half width and the collision-broadened half width. Although the peak absorbance is not accurately calculated, the line widths appear to be calculated to at least the same accuracy that can be obtained from the single-beam absorption spectrum.