Abstract: An optical cell and a method of operating an optical cell comprising employing a first mirror comprising a first hole therein at approximately a center of the first mirror and through which laser light enters the cell, employing a second mirror comprising a second hole therein at approximately a center of the second mirror and through which laser light exits the cell, and forming a Lissajous pattern of spots on the mirrors by repeated reflection of laser light entering the cell.

Abstract: An optical spectroscopy apparatus and method for measurement of species concentration, number density, or column density comprising emitting light from a laser light source, receiving light via a fixed length optical path from the source and containing a species to be detected, receiving light via a detector at an end of the path, determining one or more of species concentration, number density, and column density via signal processing electronics connected to the detector, and switching between a plurality of operational modes measuring a same absorption feature of the species depending on measured absorbance.

Abstract: An absorption spectroscopy method comprising providing a sample in a container, rotating the container, while rotating the container, directing a beam of electromagnetic radiation through the container, the beam comprising one or more wavelengths selected from the group consisting of visible wavelengths, infrared wavelengths, and ultraviolet wavelengths, and measuring characteristics of the beam after it passes through the container. Also an absorption spectroscopy apparatus comprising a container holder, a drive rotating the container holder, means for, while rotating the container, directing a beam of electromagnetic radiation through the container, the beam comprising one or more wavelengths selected from visible wavelengths, infrared wavelengths, and ultraviolet wavelengths, and means for receiving the beam after passage through the container.

Abstract: A photoacoustic spectroscopy method and apparatus for maintaining an acoustic source frequency on a sample cell resonance frequency comprising: providing an acoustic source to the sample cell, the acoustic source having a source frequency; repeatedly and continuously sweeping the source frequency across the resonance frequency at a sweep rate; and employing an odd-harmonic of the source frequency sweep rate to maintain the source frequency sweep centered on the resonance frequency.

Abstract: A photoacoustic spectroscopy method and apparatus for maintaining an acoustic source frequency on a sample cell resonance frequency comprising: providing an acoustic source to the sample cell to generate a photoacoustic signal, the acoustic source having a source frequency; continuously measuring detection phase of the photoacoustic signal with respect to source frequency or a harmonic thereof; and employing the measured detection phase to provide magnitude and direction for correcting the source frequency to the resonance frequency.

Abstract: A wavelength modulated photoacoustic spectrometry system and method comprising: generating light from a light source; passing the light through a sample area; sampling sound produced by the light passing through the sample area with an acoustic detector; and controlling wavelength of the light with a wavelength controller, wherein the wavelength controller modulates the wavelength according to a waveform comprising square components.

Abstract: A method and apparatus for demodulating a plurality of frequency components output from a photodetector in a wavelength modulation spectroscopy system and determining absorption line shapes from the demodulated data. Demodulation is performed with a homodyne demodulator. Line center magnitudes of selected even harmonics of the demodulated output frequency components are measured and the absorption line shape is calculated from the relationship between these magnitudes.

Abstract: Disclosed are a method and apparatus for dual modulation of an optical spectroscopy laser. Demodulation is accomplished in a manner resulting in measurement of absorbance of a gas species, as well as stabilization of laser wavelength and baseline noise reduction.

Abstract: An improvement to wavelength modulation spectroscopy systems operating at frequency .OMEGA. and having a photodetector generating output with frequency components .OMEGA., 2.OMEGA., . . . n.OMEGA., where n is an integer greater than one, the improvement comprising a demodulator operating at frequency .OMEGA.+.delta., where .OMEGA.>>.delta., and additionally recovering signals at n.OMEGA.+n.delta.. The system provides information on multiple detection harmonics simultaneously, no phase adjustment is needed, and the system uses a heterodyne demodulation with its inherent low-noise advantage.

Abstract: An improvement to a dual-modulation line-locking device for wavelength modulation spectroscopy employing a lowpass filter to generate a nonnormalized error signal and a bandpass filter and RMS-to-DC converter to generate a centering signal. When the error signal is approximately zero and the centering signal is large, the wavelength is coincident with the center of the absorption feature of the sample.

Abstract: The disclosure is directed to a method and apparatus for ionization modulated mass spectrometric analysis. Analog or digital data acquisition and processing can be used. Ions from a time variant source are detected and quantified. The quantified ion output is analyzed using a computer to provide a two-dimensional representation of at least one component present within an analyte.