Qinetiq Limited

The Secretary of State for Defence in Her Majesty's Government of the

Gary Cook

The need to have a large single crystal of photorefractive material for devices such as optical limiters, optical memory, and beam couplers, is avoided by providing a photorefractive body () comprising small photorefractive particles () coupled by a couplant (), for example glass, which is refractive index-matched to the particles. Such a body may comprise a fiber (), or a bulk body (). For many uses it will be necessary to align the photorefractive particles in the body and this can be achieved using fluid flows or electrostatically. Methods of making the particles, and of making photorefractive bodies are disclosed. Devices incorporating particle-couplant matrix bodies are disclosed.

Non-linear optical bodies and devices

A glass fiber () has a core () provided with Raman laser effect particles () embedded in a glass matrix (), with glass cladding () around the core. The refractive index of the glass matrix () is matched to that of the Raman laser effect particles () so as to avoid scattering. It is not necessary to have a single crystal of Raman laser material to create a laser effect in the glass fiber. A length of fiber in the order of meters or tens of meters can produce optical laser light. It is possible to have a single fiber () emit laser light at different frequencies due to Stokes and Anti-Stokes emissions. A simple laser device can therefore produce several colors of laser beams.

Laser effects and laser devices

An optical inspection system () for comparing surface structures of test and reference objects comprises a laser (), a photorefractive crystal () and a detector (). A refractive index grating corresponding to a diffraction pattern of a surface structure of the reference object is present within the photorefractive crystal () and acts as a spatial filter for light diffracted by surface structures of the test objects. If a surface structure of a test object matches that of the reference object, little or no light reaches the detector (). If the surface structure of a text object differs from that of the reference object, light of greater power reaches the detector (). The system () provides a simple pass/fail comparison test and light incident on the detector () requires no interpretation or other processing. The system () may be adapted to allow simple imaging of an edge of an object.

Optical inspection system based on spatial filtering using a refractive-index-grating

A continuous wave laser device () comprises a convoluted path or fiber () of Raman laser material that has been micromachined on to a substrate, the laser material fiber being covered by protective cladding (). A 1 cm diameter substrate can have tens of meters of fiber fabricated on it and with a suitable choice for the laser material, e.g. Diamond, can output tens of hundreds of Watts of laser power. One possible use envisaged is as multicolor laser diodes, for example for projection television systems.

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Malvern, United Kingdom

Gary Cook