GB1068515A - Laser system - Google Patents

Abstract

1,068,515. Lasers. UNITED AIRCRAFT CORPORATION. Oct. 4, 1963 [Oct. 8, 1962; April 16, 1963], No. 39103/63. Heading H1C. [Also in Divisions G1 and H4] Laser action is controlled by time varying the refractive index of the medium or a part thereof which is traversed by the laser light beam by means of ultrasound. A ruby laser element 2 pumped by lamp 4 is provided with a reflecting end coating 12 and is positioned as shown to form an optical cavity with mirror 14, an ultrasonic cell 16 being interposed between the mirrors 12, 14. If the width of the laser beam is narrower than the wavelength of the sound wave in cell 16 the laser beam is refracted back and forth in a sinusoidal manner along the plane of mirror 14 and since lasing action only takes place when the laser beam isreflected back into the system by the mirror 14, i.e. once every half-cycle of the sound wave the laser output is synchronized thereto, Figs. 2, 3 (not shown). The frequency of the lasing action may be made to vary in addition by regulating the intensity of the pumping of the laser. The elements of the system may be brought together to reduce losses, Fig. 1A (not shown). In the embodiment of Fig. 4 (not shown) both ends of the ruby (2<SP>1</SP>) are provided with reflective coatings (12<SP>1</SP>), (14<SP>1</SP>) and ultrasonic waves generated by transducer (18) are passed through the ruby to receiver (21<SP>1</SP>) so that an output of evenly spaced laser pulses is produced, the refraction of the electromagnetic radiation beam occurring internally of the ruby (2<SP>1</SP>). Fig. 1 may be modified, Fig. 5 (not shown), by deviating mirror 14 from parallelism with mirror 12 and introducing a delay between the initiation of the pumping of the laser and the excitation of the ultrasonic cell. When the electromagnetic radiation beam is refracted by the sound waves in the cell lasing action will occur with a very large burst of energy. In the absence of a sound wave lasing action is prevented. Two ultrasonic cells may be placed at right angles to each other, Fig. 6 (not shown), so as to deflect the laser beam simultaneously horizontally and vertically. If the wavelength of the ultrasonic wave is made less than the width of the laser beam then the latter is diffracted rather than refracted. In the arrangement of Fig. 8 the optical cavity of the laser is defined by reflecting end plates 152, 154 and the focal point of the curved surface of mirror 154 is such that light incident on surface 168 from aperture 166 of opaque plate 164 at the focal point of lens 162 will be reflected back through the aperture to the laser element 150. The laser beam is diffracted by the ultrasonic wave in cell 156 and the intensity of the orders of diffraction are such that the intensity of the zero order falls off almost to zero and then rises slightly as the ultrasonic wave intensity increases whereas the intensities of the higher orders of the diffraction pattern increase and decrease as a function of the ultrasonic wave intensity, Fig. 10 (not shown). If cell 156 is excited by an unmodulated output from transmitter 160 so as to set up an ultrasonic wave of sufficient magnitude to suppress the zero order then since plate 164 is placed so that only the zero order of the diffraction pattern is passed therethrough no lasing will occur. An output is obtained by removing the diffraction pattern or by reducing the intensity of the ultrasonic -wave. The laser output may be modulated by amplitude modulating the ultrasonic wave. In the embodiment of Fig. 7 (not shown) a laser output is passed through an ultrasonic cell positioned outside of the optical cavity of the laser, the ultrasonic wave being frequency modulated with the result that the sound wave acts as a diffraction grating which is moving with the velocity of the sound waves perpendicular to the direction of the emitted light. By modulating the sound wave in accordance with intelligence it is desired to transmit it is shown that the frequencies of two orders of the diffraction pattern other than the zero order are varied in accordance with the changes in frequency of the ultrasonic wave so that the light beam is frequency modulated.