An Absolute Radiometer with Uniform Response; Fabrication, Characteristics and Analysis

An absolute radiometer with uniform response over the surface of the receiver is made. Good uniformity of response is attained by suppressing heat losses transferred from the receiver to its surroundings. Suppression of heat losses is achieved by placing the radiometer in a vacuum, putting a hemispherical mirrow over the front surface of the receiver, and coating the rear surface with gold. The response varies by 0.2% over a large area of the receiver 15 mm in diameter, the sensitivity is 0.171 V/W, and the time constant is 14 s. The characteristics of the radiometer are derived entirely from a thermal model in good agreement with experimental results, and the effect of the hemispherical mirror is investigated by the Monte Carlo method from the viewpoint of radiation heat transfer. The analysis provides a guideline for making better radiometers.