NIST has invented an instrument that permits full and accurate characterization of a multi-kilowatt laser beam without attenuating it or perturbing its direction. This radiometer has been tested for laser powers up to 10 kW, but the maximum power is limited only by the irradiance allowable on the mirrors and as such, is expected to operate at much higher power levels. The unique three-mirror design allows the absolute power to be measured via radiation pressure (from the force on one mirror) while the negligibly-small fraction of light that leaks through the other two mirrors can be measured concurrently for a variety of laser beam parameters such as transverse profile, temporal response, spectral signature, etc.
Providing a vertically directed force simplifies the force calibration process and permits lower overall measurement uncertainties. Because this design redirects the laser beam to impinge on a horizontal mirror for force measurement, this allows the use of a variety of "off-the-shelf" scale technologies and force-sensors which reduces cost.
For laser beams in the anticipated power range of this instrument, there is currently no means of measuring the beam parameters in an absolute (fully-calibrated) sense without perturbing (absorbing or scattering) it. By pairing a radiation-pressure power measurement with a parasitic beam profilometer located behind one of the turning mirrors, we enable the absolute power to be measured as well as the relative beam profile. The relative beam profile can then be calibrated with the absolute power for an absolute measurement of intensity distribution. This same approach can be taken for other relative measurements such as fast power response, spectral content, etc.
Laser and Optics