Switching technology is a topic of major concern in the pulsed power community and a subject of ongoing study. Research is being conducted at the University of Texas at Arlington to investigate the possibilities of switching thyristors or silicon controlled rectifiers, SCR's, in the nanosecond time scale.; This thesis describes the optical initiation of regenerative switching of thyristors while operating at a temperature of 300K and 77K. This is the first experiment to determine the switching characteristics of a thyristor at 77K or liquid nitrogen temperatures. Emphasis is placed on the optical absorption characteristics of silicon at increased wavelengths and decreased temperatures. The optical absorption depth increases in silicon from 1mm at 1.06 {dollar}mu{dollar}m and 300K to 10 cm at 1.06 and 77K generating a substantial improvement in switching capabilities of the thyristor when operated at cryogenic temperatures. It is shown that the current rise time through the thyristor changes from 200 ns to 25 ns when the temperature is lowered to 77K and switching is initiated with laser light of 1.06 {dollar}mu{dollar}m.
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