Digital laser powermeter

Abstract

A digital powermeter was developed for measuring the power of laser beams using an electrically calibrated thermopile. This choice allows metrological quality measurements in a broad spectral range and an accurate calibration, but the electronic readout must meet some severe specifications concerning internal fluctuation (generally, most of commercially available radiometers, even advanced, do not). The reported powermeter has very low internal fluctuation (both drift and noise, in respect with its resolution). Original, yet simple circuitry was developed for low noise and for an accurate zero setting (even with a high background). The most important of these internal circuits is described. Statistical noise tests are also presented and some comparisons with advanced commercial powermeters. A large number of tests, each of them containing 500 - 900 measurements (values), revealed for the reported powermeter that `0' reading is the most probable noise value (i.e. the most often found), its probability being in all cases larger than 99% on the most sensitive range and equal to 100% on all other ranges.