Laser power measurement - Measurement techniques based on radiation pressure

The aim of this article is to present the various techniques for measuring laser power and, more specifically, the new techniques based on radiation pressure for a measurement range from a few milliwatts up to around ten kilowatts. These new techniques meet a number of industrial challenges and metrological needs, such as in-situ measurement of laser power. This measurement can be carried out without interrupting the use of the laser, over a wide range of wavelengths, from ultraviolet to infrared radiation. Power measurement via radiation pressure is traceable to SI units (International System of Units) for mechanical quantities such as length and mass.

After a few definitions of radiometric quantities and the main characteristics of a laser, the article presents the main detectors (thermal and quantum) used to measure laser power. This provides a better understanding of current industrial, medical and metrological requirements, which call for the development of new detectors based on totally different principles. From a metrological point of view, the article describes the metrological traceability of detectors, presenting, for example, the cryogenic electrical substitution radiometer, the radiometric reference of many national metrology laboratories.

The use of radiation pressure for metrological purposes is the main aspect developed here. Using a simple mirror combined with a low-force sensor, it is possible to measure, among other things, the power of a laser. The numerous developments in national metrology laboratories based on this principle open up great prospects for the realization of primary laser power standards. In addition to a complementary aspect to so-called "conventional" methods, the advantages and limitations of laser power measurement by radiation pressure are presented.