MODULATION OF A HELIUM-NEON GAS LASER.
NAVAL CIVIL ENGINEERING LAB PORT HUENEME CALIF
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The modulation of a 38-cm gas phase laser operating at a wavelength of 6,328 angstroms was accomplished through the use of amplitude modulation techniques. The modulation was applied directly to the DC-excited plasma tube through a suitable transformer in series with the tube and power supply. Modulation was limited by the natural Gaussian frequency distribution of the doppler-broadened gas plasma and by optical beat notes occurring in the output beam of the laser. The experimental results obtained with ammonium dihydrogen phosphate crystals used as optical modulators are reported. Minimum light shutter action has been observed when as much as 6 kv was applied to the faces of thin crystals. The modulated light beams were detected with photomultiplier and associated circuitry. The photomultiplier has been used to observe modulation products on the laser beam at bandwidths of 50 to 100 MHz, but optical beat notes on the unmodulated beam have been detected at frequencies up to 394 MHz. Observation of the low-frequency part of the spectrum has disclosed the presence of a shot-noise level whose magnitude varies as the inverse of the output frequency. Author
- Lasers and Masers