Abstract: An optical arrangement includes an infrared imaging system operating in conjunction with a first beam having wavelengths less than 15 microns, and a coherent infrared source generating a second beam having wavelengths shorter than the first beam wavelengths. Also provided is an objective lens arrangement including an objective lens having an aperture formed in one side of the objective lens. A partially reflective member is located between the objective lens arrangement, and the imaging system and infrared source. A T.V. camera is provided for receiving an image through the objective lens aperture. The first beam is directed to the imaging system from a region being imaged, and the second beam is directed from the infrared source to the region being imaged. The respective beams are directed to the partially reflective member so as to cause the respective beams to pass through the objective lens along substantially the same optical path as each other.

Abstract: Detector apparatus includes a diffraction grating (11) having a period such that the incidence of coherent point-source radiation upon it produces a number of spaced self-images of the grating behind it. A Moire grating (12) is placed to coincide with one of these self-images and a detector array (13-16) is placed behind the Moire grating to detect the resulting interference fringes.

Abstract: Detector apparatus includes a dispersive prism (10) and a diffraction grating (11) of the type which produces only zero and first order diffraction patterns. Located behind the diffraction grating (11) so as to interact with the first harmonic content of the diffraction patterns is a Moire grating (12) having half the pitch of the diffraction grating (11). Detector means including at least two pairs of detectors (13-16) is located behind the Moire grating (12) to detect the presence of Moire fringes.

Abstract: An optical element for location between a source of radiation and a detector (13) includes a first optical surface (10) have a central transmissive area (11) and a surrounding area (12) reflective to radiation from direction of the detector (13). A second optical surface (15) is spaced from the first surface (10) towards the detector (13) and has a central reflective area (16) arranged to reflect radiation passing through area 11 towards the reflective area 12. A transmissive area (18) of the second surface (15) surrounds the central area (16), and is itself surrounded by a reflecting area (17) concentric with the detector (13) and forming a reflective shield for the detector.