Abstract: The present invention relates to a method and apparatus for starting and maintaining a long electrical arc in an arc chamber containing a few atmospheres of pressure of an ionizable gas. An electrical potential difference is maintained between two fixed primary electrodes while a short arc is created between the first primary electrode and a pilot electrode, creating ionized gas. The ionized gas is caused to flow towards the second primary electrode thus creating a region of ionized gas between the two primary electrodes, and hence causing a long arc to be struck. This method does not require relative electrode movement as was the case previously.

Abstract: Avalanche photodiodes include a substrate of a high resistivity material having at least a first surface. The substrate is of a particular conductivity type. In the substrate and at the first surface are a plurality of spaced apart regions of the same conductivity type as the substrate and defining the individual photodiode elements of the avalanche photodiode. Occupying the area at the first surface of the substrate not occupied by the spaced regions and extending into the substrate is a discontinuous layer of the same conductivity type as the spaced regions but of a conductivity concentration much lower than the conductivity concentration of the spaced regions. On the first surface of the substrate covering the discontinuous layer and slightly overlapping the spaced regions is a patterned passivation layer. The improvement of the present invention over the prior art is the addition of the discontinuous layer which reduces the electrical noise in the output signal of the avalanche photodiode.

Abstract: In an electro-optic laser beam modulation system wherein the polarization modulation of the laser beam is converted into intensity modulation by an analyzer positioned in the path of the beam, a pair of photo-electric detectors detects a portion of the input and output beams. A divisor registers the ratio between the intensities detected. A compensator rotates the polarization of the output beam to establish a desired ratio, and a comparison system is connected to the divisor and the compensator to maintain the desired ratio.

Abstract: A communication system uses a laser beam directed along a path and a retrodirective reflector to return the beam along the same path. The front face of the retrodirective reflector is covered by a layer of an electro-optic material which, in response to an electric field produced by a vidicon, modifies the reflectivity of the reflector. The laser beam, when passing through the electro-optic material, is modulated by the output of the vidicon, and the modulated beam is returned along the given path to a suitable receiving means.