An off-axis transmission holographic scheme, in which a 1:1 lens and a hologram are treated as a single rigid entity, is found to reconstruct a 3-D diffraction-limited image when reconstructed, with a reference beam reversed back through the original lens–hologram unit. Reconstruction can be performed with wavelengths other than the recording wavelength, provided achromatic lenses are used, and the reference beam angle is properly changed for reconstruction. Comparisons are made between He–Ne and ruby laser holograms. Two-micron resolution of the combustion of solid rocket propellants at high pressures is achieved at a working distance of 6 cm.
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