Abstract: A display assembly includes a display screen having a predetermined generally planar area for displaying transmissive data. A light source is provided for generating light of predetermined intensity, and a circular Fresnel lens is disposed between the light source and the display means, the circular Fresnel lens imaging the light source through the display means and onto an opposite side of the display means. A diffuser is disposed between the light source and the display means for diffusing the light. The intensity of the light source is selected to be appropriate for direct human viewing of the transmissive data.

Abstract: A coherent tunable narrow band IR source in the vicinity of 16 .mu.m is achieved by four-wave parametric mixing in parahydrogen. A pair of colinear laser beams, one from a narrow band CO.sub.2 laser, and a second from a multiline laser with output of wave number significantly below 14,400 cm..sup.-1, is focused in a parahydrogen containing cell. The multi-line laser beam drives a Raman process in the cell. The narrow band CO.sub.2 input beam mixes with this driver beam and the Stokes wave resulting from the Raman process to produce a 16 .mu.m output beam. Tuning of the CO.sub.2 laser allows tuning of the 16 .mu.m radiation emitted by the parahydrogen cell.

Abstract: An intense broadband continuum light pulse of uniform spectral intensity and short time duration is generated. This continuum pulse is then downconverted in frequency to a region of interest, preferably in the infrared region, by applying it as a pump pulse to a molecular or atomic vapor so as to induce stimulated Raman scattering. The resulting Raman Stokes pulse surprisingly tends to have the same spectral bandwidth, intensity uniformity and time duration as the pump continuum pulse.The downconverted continuum pulse (the Raman Stokes pulse) is then used to probe a sample. The sample converts the uniform spectral intensity distribution of the probe pulse into a nonuniform spectral intensity distribution which contains the absorption spectrum of the sample. This spectrum pulse has the same spectral bandwidth and time duration as the Raman Stokes pulse and is finally upconverted in frequency to a region where the spectrum pulse can be conveniently recorded.