Experimental and theoretical investigations of the spontaneous infrared radiation fluctuations of a high-pressure, high-current argon discharge.
The equations describing the spontaneous fluctuations of photon radiation are given by the Bose-Einstein statistics. These equations are applied to calculate the statistical fluctuations of photon radiation emitted by a nonhomogeneous plasma. By using a photodetector, the radiation fluctuations are transformed into corresponding output current fluctuations. The detector must have special properties as to sensitivity, noise, frequency response, and transmission characteristics. The InSb photodetector described here has the required properties. As a radiation source, the plasma of a stationary argon arc discharge at high pressure was used. By measuring and calculating the continuous photon radiation, it is possible to determine the temperature distribution in the plasma. Investigations of the electrical conductivity confirm the temperature distributions. Because of the high temperatures, as well as the sufficient optical thickness in the infrared spectral range, determination of the fluctuation factors is made possible. Considering the experimental difficulties, the agreement between measured and calculated factors is good. Instabilities in the plasma have been considered and eliminated in the experimental procedure.