Thermal Mode of Sapphire Shells and Depth of Modulation of Radiation of Pulsed-Periodic Sources of Infrared Radiation

The factors that determine the two most important characteristics of powerful infrared radiation sources, peak power and the depth of the radiation modulation in the spectral regions 1.8--4.2 μm and 3.0--5.0 μm, are investigated. The distributions of temperature fields in the discharge channel and in the system of two sapphire shells separated by a gap with the gas are given. It is shown that in the pulsed-periodic mode of operation with a pulse repetition rate of 450 Hz, the temperature field in the heated shells is practically stationary and causes, at high electric powers, the appearance of a constant radiation of the material of shells. As a result, the fraction of the discharge radiation in the total radiation of the source decreases, which negatively affects the depth of modulation. The temperature drop over the wall thickness is much smaller than the temperature difference in the gas gap. Data on the time dependence and the structure of heat losses on the inner shell are given. The spectral dependence of the depth of modulation is obtained under conditions of different cooling intensities, it is established that starting from about 4.9--5.2 μm, the lamp practically loses modulation properties in the infrared region. In this case, a sharp decrease in the depth of modulation begins from wavelengths of about 3.5 μm. The methods and design solutions that contribute to the increase of the modulation depth due to the reduction of the constant component of the radiation and the increase in the peak power of the radiation are considered in detail. The results obtained make it possible to reduce the laboriousness of experimental work in designing devices of this type

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