Ferranti Plc

Gec Ferranti Defence Systems Limited

Hillary G Sillitto

John C Parker

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.

Detector apparatus for detecting coherent point-source radiation

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.

Detector apparatus for detecing coherent monohromatic point-source

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.

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Hillary G Sillitto