Measurements have been taken of the radiative flux density, the spectrum, and the temporal behavior of laser induced underwater sparks. When a 30-MW Q-switched ruby laser was focused into water, the resulting spark revealed a blackbody-like spectrum with a temperature of 15 000°K. The spark was delayed in time by 15 nsec with respect to the laser pulse and had a temporal behavior very similar to the laser pulse producing it.

A comparison of projected thermoelectric and thermionic refrigeratorsA theoretical analysis of single-barrier thermionic emission cooling in semiconducting materials is performed using Fermi-Dirac statistics. Both maximum cooling and coefficient of performance are evaluated. It is shown that the performance of a thermionic refrigerator is governed by the same materials factor as thermoelectric devices. For all known materials, single-barrier thermionic refrigeration is less effective and less efficient than thermoelectric refrigeration.

Specific contact resistance measurements are reported for Al-Ti ohmic contacts to epitaxial p-type 6H-SiC as a function of epitaxial doping. The circular transmission line method was used to measure the specific contact resistance including the sheet resistance of the epitaxial layer and the modified sheet resistance under the contact. Epitaxial layers with Al doping between 5.5×1015 and 2×1019 cm−3 yielded specific contact resistances between 2.9×10−2 and 1.5×10−5 Ω cm2. A good theoretical fit to the contact resistance data was obtained by assuming the metal-6H-SiC barrier height to equal 0.37 eV.

Saturation of the junction voltage has been observed to occur at the onset of lasing in cw stripe-geometry (AlGa)As double-heterostructure junction lasers. Simultaneous measurements of the nonlasing but amplified spontaneous emission confirm that saturation of the optical gain and spontaneous emission accompany the voltage saturation as expected. With well-behaved lasers the observed saturation is maintained over currents to at least 50% above threshold. In other devices, a loss of saturation is commonly observed to occur simultaneously with a nonlinearity in the current dependence of the lasing emission.

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