Abstract: A modular system for gas analysis has a first gas cell that receives and passes at least a portion of an infrared light beam through at least a portion of the first gas cell. A second gas cell disposed proximal to the first gas cell receives and passes at least a portion of the infrared light beam from the first gas cell through at least a portion of the second gas cell. At least a portion of the first gas cell and at least a portion of the second gas cell define a light path having an effective length. The system includes a means for adjusting the effective length of the light path to vary a property of the infrared light beam. Methods of making a variable effective length light path and methods of making a gas detector are also disclosed.

Abstract: A method and apparatus is disclosed for signal spectrometry using an improved apodization function. Such method and apparatus involve (i) obtaining sample and reference time domain waveforms; (ii) applying sample and reference apodization waveforms to the sample and reference time domain waveforms, such that substantially same weight is applied to corresponding substantially coextensive regions of the sample and reference time domain waveforms, (iii) transforming the sample and reference apodized waveforms from the time domain into the frequency domain; and (iv) generating referenced spectral analysis waveform for signal analysis from a ratio of the transformed sample and reference frequency spectra, the spectral analysis waveform substantially excluding frequencies associated with the corresponding substantially coextensive regions of the apodized sample and reference time domain waveforms.

Abstract: A method and apparatus for spectral identification of a material based on a spectral signature. The method is ideally suited for thin film substrate characterization, as found in semiconductor wafer and optical thin film processing.