1983 Volume 22 Issue 6 Pages 508-521
The measurement of radiant power output from laser is becoming more important to manufactures and users of laser, because of the increasing applications of laser.
For the purpose of making precise measurement and setting standards of the laser power, calorimeters using the dc power substitution method have been developed in several national laboratories in the world. The common problem encountered in the calorimetric techniques of laser power measurement is that it is very difficult to evaluate the amount of dc power to be substituted for laser power since the surface reflectance of the absorber and other complexities including thermal equivalence relationship between laser and dc power remain unknown.
In this paper, calorimetric methods for precise measurement of laser power are surveyed, and a new double calorimeter designed to establish the CW laser power measurement standard is discussed. The double calorimeter consists of a standard thermopile unit (conduction-type calorimeter) having fast response and an electronic-cooling calorimeter (isothermal-type calorimeter) of which the thermal load is borne by the thermpoile unit. In a description of the principle of the double calorimeter, the substitution ratio of dc power for laser power (which is termed the effective efficiency) in the thermopile unit is defined. The thermopile unit and the electronic-cooling calorimeter are operated simultaneously, and the effective efficiency of the thermopile unit is determined.
The details of study on the optical and thermal characteristics of the unit to obtain the optimum structure and performances are newly described. The specifications of the unit to be used for precise measurement in the low power (1-50mW) and the medium power (0.03-1W) ranges are described. For the measurement system, a twin-type calorimeter is discussed in detail. Various errors related determining the effective efficiency are theoretically and experimentally evaluated. We obtained the systematic errors of ±0.27% for the low power range and ±0.42% for the medium power range respectively. The international comparison of He-Ne and Ar laser power measurement conducted by Electro-Technical Laboratory as the pilot laboratory is also described.
