Abstract: Self-normalization of laser spectrometers is provided by I"/I laser modulation and detection. A single tunable diode laser is frequency modulated by a high S/N ratio triangle wave, mechanically chopped, passed through an isothermal in-line gas and reference chamber absorption cell, and synchronously detected to provide the I" and I signals. The preferred embodiment discloses isotopic ratio measurements. The invention has application to quantitative trace gas measurements generally.

Abstract: A scanning spectrometer incorporating a scanning diode laser powered with a controllable injection current. The injection current control may be set at predetermined discrete levels. These levels may be varied in accordance with signals derived from a servo loop, and may have superimposed upon them a cyclically varying substantially constant amplitude current. The laser output is directed via a beam splitter to both sample and reference cells. The material in the reference cell is so selected as to provide absorption features at each of the desired frequencies. The cyclically varying current is provided with an amplitude sufficient to cause a frequency amplitude at least as great as the maximum breadth of each of these spectral features of interest. The preselected bias currents are selected so as to provide lasing action of the diode at or near each of the selected frequencies.

Abstract: A system for analyzing a time-varying phenomenon in which the latter is repetitively initiated to provide a train of repetitive output signals. A fast Fourier transform interferometer is provied to scan the train. Data corresponding to a selected temporal resolution element having the same selected time position following initiation of each signal are sampled and the samples coded to improve signal-to-noise ratio. The time relation between a selected retardation point in the interferometer and the initiation of each signal in a given train is successively shifted so as to produce a series of coded data, each datum corresponding to a resolution element occurring at the selected time position but at a different interferometer retardation. The selected data are then assembled in their time sequence to generate a synthetic interferogram.