An imaging Fourier transform spectrometer (10, 210) having a Fourier transform infrared spectrometer (12) providing a series of images (40) to a focal plane array camera (38). The focal plane array camera (38) is clocked to a multiple of zero crossing occurrences as caused by a moving mirror (18) of the Fourier transform infrared spectrometer (12) and as detected by a laser detector (50) such that the frame capture rate of the focal plane array camera (38) corresponds to a multiple of the zero crossing rate of the Fourier transform infrared spectrometer (12). The images (40) are transmitted to a computer (45) for processing such that representations of the images (40) as viewed in the light of an arbitrary spectral "fingerprint" pattern can be displayed on a monitor (60) or otherwise stored and manipulated by the computer (45).

An optical scanner for use in conjunction with an infrared spectrometer is disclosed. The optical scanner translates a beam of radiation to a stationary spot on a traveling sheet of material so that ample integration time within the spectrometer is achieved. The beam path impinges on the traveling web and the radiation is reflected off the traveling web back through the optical scanner and recombined at an interferometer. The beam of radiation is kept stationary with respect to both the traveling sheet and the carriage which houses the spectrometer.

Temperature measurements of sheet material such as paper can be obtained directly from an analysis of the absorption spectrum of water in the infrared region. The technique is based in part on the recognition that the central wavelength position of a selected moisture peak is dependent upon the sheet temperature; the wavelength position also has a known temperature sensitivity. Thus, once the wavelength position of this moisture peak is ascertained, the moisture temperature of the product being monitored can be calculated. The position of the moisture peak is preferably obtained from the derivative of the peak. By measuring the size of the infrared absorption and the wavelength position of the absorption peak, both the moisture content and the moisture temperature of the sheet material can be determined. The data is used for process control. Tunable laser diodes are particularly suited as the source of infrared radiation for the temperature sensors.

An optical translation technique for moving the interrogation spot at which a triangulation system measures the displacement of a target is disclosed. In normal operation of the laser triangulation sensor, an incident laser beam is projected from a sensor head onto a surface of a web that is facing the sensor head. Radiation is reflected from the surface and detected by the sensor. The distance from the sensor head to the web surface is calculated by triangulation. With optical translation, both the incident ray path and the captured ray path are translated with a plurality of high refractive index geometries such that the nominal functioning of the triangulation sensor remains undisturbed. The optimal position on the sheet wherein the interrogation spot will be located can be ascertained.

A sensor for measuring at least selected component in a composition can include: (a) a broadband light source, (b) an acousto-optic tunable filter (AOTF), (c) means for generating a beam of light from the light source and directing the beam of light at the AOTF wherein the AOTF is tuned to pass detection light having a desired wavelength range to detect the presence of the at least one component in the composition, (d) means for directing the detection light of known wavelength to the composition, (e) detection means for receiving light that emerges from the composition, and (f) a control signal generator configured to provide the AOTF with at least one desired wavelength range that is characteristic of the least one component in the composition. As an example, the sensor can be used to measure the thickness of optically transparent films.