Block Engineering, LLC

Spectra-physics Gmbh

Laser Analytics, Inc.

Arlan W Mantz

David L Wall

Kenneth W Nill

Richard S Eng

Dudley M Chapman

John C O'Connell

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.

Self-normalizing single-beam laser spectrometer

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. A phase-locked amplifier tuned to the frequency of the cyclically varying current senses the position of the scanned laser output relative to that of the associated absorption feature and provides an error signal to adjust the bias current so as to center the cyclically scanned laser frequency on the selected absorption feature.

Scanning laser spectrometer

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. The synthetic interferogram, when inversely transformed, provides the spectrum of the phenomenon as it occurred during the temporal resolution element at the selected time position.

System for analyzing time-dependent phenomena

A system for analyzing a time-varying phenomenon in which the latter is repetitively initiated and a spectral output is generated during the course of each successive phenomenon. The output spectrum is repetitively scanned by a fast Fourier transform interferometer to produce an interferogram. The time relation between a selected retardation point in the interferometer and the initiation of each phenomenon is successively shifted so as to produce an ordered set of interferograms each representing a different time relation between initiation and scanning. Data corresponding to a selected temporal resolution element having a fixed time position following initiation of the phenomenon are selected from each of the ordered set of interferograms and the selected data are then reassembled in the same order as the interferograms from which they were taken, to produce a synthetic interferogram. The synthetic interferogram, when inversely transformed, provides the spectrum of the phenomenon as it appeared during that selected temporal resolution element.

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Acton, MA, United States of America

Arlan W Mantz