GB947568A - Light control arrangement - Google Patents

Abstract

947,568. Optical ranging; optical masers. F. FRUNGEL. Oct. 2, 1962, No. 37247/62. Headings H3B and H4D. The distance between a given point and a distant object is measured by directing light pulses at a predetermined pulse frequency from said given point to the distant object to be reflected thereby, observing through a light valve, at an observation point close to said given point, the said light pulses as they are reflected by said distant object and returned to said observation point, alternately opening and closing said light valve at a frequency identical with that of the light pulses, adjusting the phasing of the opening and closing to provide a delay relative to the production of the light pulses such that they display a maximum relative intensity as viewed through the light valve, and measuring the delay to provide, in consideration of the known velocity of light, an indication of the distance from the given point to the distant object plus the distance from said object to the observation point. In the apparatus shown in Fig. 2, the light pulses are produced by a spark gap device 10 under the control of a quenched spark gap device 11 and timing control 9. The excitation voltage is produced by an A.C./D.C. power pack 12 and a tank capacitor 13. The current passing across the spark gap also passes through the primary of an impulse transformer 14, the current pulse having the shape shown in Fig. la. The impulse transformer is constructed to produce at its output, the first derivative of the input, the voltage pulse at its output thus being as shown in Fig. 1b. This pulse is delayed by fixed delay lines 16<SP>11</SP> and variable delay line 16, before being applied across the plates of a Kern cell 3 in the form of the pulse shown in Fig. 1c. The light pulse produced by spark gap 10 is directed towards the distant object 101 and is reflected thereby to be picked up by the Kerr cell arrangement which comprises a first polarizing filter 4a, the Kern cell 3, and a second polarizing filter 4b, having its plane of polarization at 90 degrees to that of filter 4a. When a voltage is applied across the Kern cell plates the plane of polarization of light passing therethrough is twisted through 90 degrees. The arrangement will thus act as a light valve, opening when a voltage is applied across the Kern cell. In use delay line 16 is adjusted until the opening of the Kern cell light valve coincides with the return of the reflected light pulse, as determined by maximum light intensity being observed by an observer 103 through telescope 104. The propogation distance can then be determined from the delay induced by delay lines 16<SP>11</SP> and 16 and the velocity of light. In a second embodiment, Figs. 3 and 4, the light pulse source is a laser, comprising a tubular ruby crystal 24 surrounded by a plurality of parallel connected light tubes 23, and with a single light tube 23a running down the centre of the cylinder. The ruby and light tubes are enclosed in a conductive cylinder 22a forming one electrical connection for the light tubes and giving the arrangement a small inductivity. A light intensity measuring device may be substituted for the observer 105 with its output controlling the adjustment of the delay line 16. Specification 719,296 is referred to.