GB996555A - Improvements in or relating to apparatus for assisting vision under conditions of poor visibility - Google Patents

Abstract

996,555. Television. GENERAL ELECTRIC CO. Ltd., and E. R. THOMAS. Feb. 26, 1964 [March 14, 1963], No. 10245/63. Heading H4F. Apparatus for assisting vision under conditions of poor visibility, e.g. fog or mist, comprises a pulsed light source 1 and a photoelectronic image converter 2 having a control electrode or gate to which is fed a control signal from a control signal generator 3 so that the converter does not produce a visible image in response to the light received by it during the period and immediately following the period when each pulse of light is emitted from the source, the arrangement being such that only light that is reflected back from beyond a critical distance from the apparatus causes the converter to produce an image. Light source 1 may be a current stimulated gallium arsenide diode in a lasing or a non-lasing mode, a light stimulated laser or a gas laser, which emits regularly recurrent flashes of light 4, Fig. 2, of short duration t e.g. of a few nanoseconds, at a rate of once every microsecond, the light being in the visible or near-visible part of the spectrum. Curve (b), Fig. 2, shows the waveform of the control signal pulses 5 supplied by generator 3, each pulse being of duration T nanoseconds spaced x nanoseconds apart, the frequencies of flashes 4 and pulses 5 being the same. As only light received by intensifier 2 during intervals between pulses 5 produces an image, only the light reflected back from objects beyond a certain distance l from the apparatus will produce images. Thus object B produces an image but object A doesn't, thus avoiding the back scatter of light from near fog particles. The fluorescent material on the screen of the intensifier 2 preferably has a short response time and a relatively slow decay.