(a) Model to explain photoemission in CsBr/metal photocathodes with photon energy less than the band gap. (b) Model to explain the photoemission in photocathodes with photon energy less than the band gap.
(a) Behavior of a sample with time operating at an initial current density illuminated with a laser. (b) Behavior of a sample at a current density illuminated with a laser. The sample was previously operated for more than under similar conditions. The fluctuations in the photoyield are due to laser spot motion due to floor vibrations and laser power changes due to a defective laser cooling system.
Behavior with increasing temperature of the photocurrent vs time (seconds) of a sample (upper) and with decreasing temperature (lower). The upper figure data were obtained during illumination with a focused laser beam after a wire heater built inside the sample holder was turned on. The heat was stopped after about when the sample holder reached over . The lower figure was obtained during the cooling cycle. In both cases the UV laser beam was interrupted at controlled intervals to study beam blanking effects. A similar behavior was observed utilizing infrared laser heating with the IR beam illuminating simultaneously the focused laser spot on the sample.
Model geometry and parameters utilized for the laser heating calculations of the sample on a sapphire substrate. A temperature dependent thermal conductivity for sapphire was utilized.
(a) Calculated temperature distribution on the GaN sample caused by illumination with a radius laser spot at . Results are presented for two different incident laser powers. The maximum temperature of the heated spot is shown in the figure. (b) Calculated dependence of the maximum spot temperature with laser beam radius.
Model geometry and parameters utilized for the laser heating calculations of the sample on a diamond substrate.
Calculated maximum temperature of the GaN sample with sapphire and diamond substrates.
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