Abstract

Methods used at the National Bureau of Standards for determining the power or energy in laser beams depend on calorimetric comparison of laser power or energy and the calibrating electrical power or energy. For this comparison, it is essential to know the fraction of the incident radiant energy that is converted to heat and measured by the calorimeter. This fraction, the effective spectral absorptance, is measured by adding an auxiliary calorimeter, which covers practically all of the opening in the main calorimeter. A laser beam enters the main calorimeter through a small hole in the auxiliary calorimeter. The reflected laser energy and the excess thermal radiation are measured by the auxiliary calorimeter. The data analysis is based on the theory of calorimetry derived from a linear heat-flow problem. Time-dependent functions relating the transient temperature responses of the calorimeters to various constant power inputs are determined experimentally from known electrical inputs. The effective absorptance is found by comparing transient responses for electrical and laser inputs.

© 1975 Optical Society of America

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