Abstract: A method of making a light equalizer comprises the steps of mixing two different powdered crystalline materials, each of a slightly different index of refraction so as to provide scattering of selected wavelengths of light. The materials are compacted under pressure to form an integral body containing a plurality of light scattering centers. The exterior surfaces of the body are covered with a reflective coating except for two opposite ends through which the selected wavelengths of light can be transmitted so as to provide a substantially uniform distribution of light at its output.

Abstract: A methane detector comprising a He-Ne laser in which the plasma tube forms a portion of the resonant cavity and the laser can be stimulated to emit at two different atomic resonances at separate wave numbers .nu..sub.1 and .nu..sub.2, one of which is more strongly absorbed by methane than the other. Means such as a beam splitter disposed in the resonant cavity, are provided for directing two beams outwardly from the cavity to a pair of detectors each provided in the path of a respective beam. The cavity is tuned so that its length L meets the criterion m/2L = .nu..sub.1 -.nu..sub.2, m being a number of half integers. Means are provided for cyclically varying the gain of the laser across one free spectral range through some tuned center value.

Abstract: An optical system is provided to minimize the angle-dependent transmission characteristics of interference filters, the optical system including a light equalizer having an output aperture across which each area element exhibits substantially the same emission intensity regardless of the distribution of light into the input aperture of the equalizer. The output aperture of the equalizer is disposed at the focal surface of collimating optics and the resultant collimated light constitutes the input to the interference filter.The equalizer is embodied in a transmissive element which is divided into pairs of transmissive channels, the number of such pairs increasing with the distance from the input aperture. The interface between the adjacent channels is, at least in part, leaky as by being substantially half transmissive half reflective. The exterior surface of the equalizer is covered with an internally reflective coating except for the input and output apertures.

Abstract: A light equalizer having an output aperture across which each area element exhibits substantially the same emission intensity regardless of the distribution of light into the input aperture of the equalizer. The equalizer is embodied in a stack of a plurality of transmissive elements, a number of which provide a multiplicity of light scattering centers. The exterior surface of the equalizer is covered with an internally reflective coating except for the input and output apertures.