GB1251424A - - Google Patents

Abstract

1,251,424. Lasers. DEFENCE SECRETARY OF. 19 Feb., 1970 [21 March, 1969], No. 14934/69. Heading H1C. A laser has an electro-optical Q switch controlled by a step waveform so that each step alters the laser cavity Q by a discrete amount and produces a laser output pulse. The laser rod L, Fig. 1, is pumped by a flash tube F, each flash being initiated by a pulse from a timing circuit activates generator G to apply a stepped waveform being separated by a time interval short compared with the fluorescence lifetime of the laser material. The Q switch comprises a Pockels or like cell P2 and a calcite polariser P1, oriented so that with a voltage applied to the cell light is not transmitted through the switch. The voltage is derived from a supply rail through a high resistance R1, Fig. 2, and the cell may be shorted by pentodes V1, V2. The timing circuit T applies two pulses to the pentodes so that first V1 then V2 conducts and a step waveform appears across the cell. The first part of the waveform renders the Q switch partially tranmitting, and the second part renders it wholly transmitting. The two laser output pulses thus produced may be made the same amplitude by adjusting R5. The time between pulses may be altered in the range 30 nanosecs to 6 Á sees without loss of efficiency. The pentodes of Fig. 2 may be replaced by cold cathode discharge tubes or by thyratrons.