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Epitaxial single-crystal chemical-vapor-deposited diamond with ͑100͒ crystal orientation is obtained from Element Six ͑Ascot, United Kingdom͒ and Apollo Diamond ͑Boston, Massachusetts͒. Both companies supply 5 ϫ 5-mm squares with thicknesses of 0.35 to 1.74 mm. Element Six also provides disks with a state of the art diameter of 10 to 11 mm and a thickness of 1.0 mm. The absorption coefficient measured by laser calorimetry at 1.064 m is 0.003 cm −1 for squares from Element Six and 0.07 cm −1 for squares from Apollo. One Apollo specimen has an absorption coefficient near those of the Element Six material. Absorption coefficients of Element Six disks are 0.008 to 0.03 cm −1 . Each square specimen can be rotated between orientations that produce minimum or maximum loss of polarization of a 1.064-m laser beam transmitted through the diamond. Minimum loss is in the range 0 to 11% ͑mean =5%͒ and maximum loss is 8 to 27% ͑mean= 17% ͒. Element Six disks produce a loss of polarization in the range 0 to 4%, depending on the angle of rotation of the disk. Part of the 0.04 to 0.6% total integrated optical scatter in the forward hemisphere at 1.064 m can be attributed to surface roughness.

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The advent of non-linear photonic crystal fibres with engineered optical properties has enabled the production of compact high-brightness super-continuum sources with a spectral power density in excess of 1 mW/nm throughout the visible and near-infrared spectral regions. Such sources have intrinsically good beam quality and, when properly collimated, the various spectral components propagate in a co-linear fashion, thus retaining spectral fidelity along the beam path. These properties are ideal for an active hyper-spectral remote sensing system.We report the construction and testing of a white light transceiver for measurement of the spectral reflectivity of remote targets. The transmission section of the transceiver comprises a commercial white light source with apochromatic optics to ensure simultaneous collimation at all wavelengths. The receiver section comprises a telescope coupled to a fibre-optic visible band spectrometer. A portion of the received light is directed onto a camera to facilitate accurate pointing of the system. The transceiver has been used to measure the spectral reflection from both diffuse and retro-reflecting targets at an outdoor range. The spectral return from retro-reflective targets was successfully measured at ranges up to 1.2 km. For diffuse targets, the useful range was limited to a few hundred metres, beyond which the signal was dominated by ambient daylight. The propagation of the white light beam along the 1.2 km has been studied. The fidelity of measured spectra was affected by atmospheric turbulence which caused the beam to break up into a time-varying pattern of coloured regions. This effect imposed a lower limit on the integration time required to measure individual spectra, independent of the signal to noise ratio.

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