Laser pulse code communication

If a 3-kHz bandwidth is assumed for voice communication by PCM, and a 16-level (4 bit) quantization for an intelligible pulse code format, the gas laser must be capable of a minimum pulse rate of 30 kHz. To attain such a high pulse rate, it is necessa.ry to reduce the pulse width while increasing the repetition rate. An argon gas laser was built with the capability of changing the pulse width, the peak input current and the argon gas pressure. The various laser parameters were measured and studied to determine the optimum conditions for a PCM laser system. The five strong argon lines of 5145, 5017, 4965, 4880, and 4765 radiated from a confocal cavity using an air-cooled fused quartz tube whose active length is 14.5 inches. The gas was ionized with a 6-kV pulse applied to a coil of wire wrapped around the quartz tube. Both ends of the tube were connected to a gas reservoir to reduce gas pumping problems. A hot cathode with a capacitor at the anode provided the pulsed current to excite the plasma.