GB1073179A - A laser - Google Patents

Abstract

1,073,179. Lasers. INTERNATIONAL BUSINESS MACHINES CORPORATION. Oct. 27, 1964 [Oct. 31, 1963], No. 43685/64. Heading H1C. A laser is pulse-frequency modulated by means of an electro-optic crystal included within the laser cavity. As shown in Fig. 2, a laser comprises a ruby crystal 22 surrounded by a pulsed helical flash lamp 24 which may have conventional reflecting and cooling accessories. A beam of stimulated radiation 25 may pass through a polarizing prism 28 having a vertical transmission plane: alternatively, if a 90 degree or 60 degree oriented ruby is used, the polarizing prism is unnecessary. Lenses 30, 32 reduce the plane-polarized beam which passes into a cylindrical waveguide cavity 34 containing centrally an electro-optic crystal 38 having a linear electro-optic effect and a high electrooptic coefficient such as NH 4 H 2 PO 4 , KH 2 PO 4 or KD 2 PO 4 . A generator 18 generates a frequency-modulated microwave signal bearing information which signal is applied to a probe 35 to excite the cavity 34 in its TM 01 mode. The cavity 34 has an axial length equal to an integral number of half-wavelengths of the microwave carrier and a low-loss dielectric 36 such as fused quartz is used to match the phase velocity of the standing microwaves with that of the stimulated radiation. The spacing of the Fabry-Perot reflectors 40, 42 is such that the time for propagation of radiatoin between them is equal to an integral number of half-periods of the microwave carrier. The state of polarization of stimulated radiation re-entering the ruby crystal after reflection from the reflector 42 is modulated by the microwave field within the cavity 34. In Fig. 3 (not shown) laser pulses 50 are emitted from partially reflecting surface 40 twice per microwave cycle when the microwave field is substantially zero. There is described with reference to Figs. 4 and 5 (not shown) an embodiment in which a birefringent bias plate (52) is inserted in the beam between the ruby crystal and the modulator; only one fourth as much modulator power is required but laser pulses are emitted only once per microwave cycle.