GB1272234A - An optical image intensifier - Google Patents

Abstract

1,272,234. Lasers. NIPPON SELFOC CO. Ltd. 4 Aug., 1969 [22 Oct., 1968], No. 38968/69. Heading H1C. [Also in Division G2] A laser amplifier comprises as an active medium a rod 6 whose refractive index n decreases from a maximum value N according to the square of the distance r from its axis, as given by the equation n = N(1-ar<SP>2</SP>) where a is a positive constant. Such a refractive index gradient is stated to cause the medium to act as a series of convex lenses. The amplifier is incorporated in an image intensifier, Fig. 1, an object P being illuminated by light transmitted from a source 12 through a fibre guide 2. An image Q 1 is formed by a lens 4 and transmitted through a fibre guide 3 to the laser amplifier 5, which comprises a neodymium doped glass rod 6 and a pump 7. The image is projected on to a film or screen 8. Each of the fibres in guides 2 and 3 preferably has a refractive index variation given by the above equation, as described in Application No. 38648/69. In another embodiment, Fig. 2 (not shown), guides 2 and 3 are replaced by a common fibrous body having the above refractive index variation. The light source 1 may be a laser generator with an output suitable for amplification by rod 6, such as a neodymium doped YAG, or may be a white light source. In the latter case a filter may be used which passes only radiation suitable for amplification by rod 6, thereby minimizing heating of the object P. If the fibre guide 3 is long, laser amplifiers may be disposed therein at intervals. An optical isolator such as a Faraday effect device may be used at the input of the intensifier to prevent effects of backward radiation. The rod 6, and the common guide of the second embodiment, may be made by the method described in Specification 1,269,101.