Researchers at the National Institute of Standards and Technology (NIST) have been developing a novel way of measuring laser power. Their device, called the Radiation Pressure Power Meter (RPPM), makes its measurements using the force exerted by the laser light itself.
The NIST team has now fully tested this instrument at the highest power to date – 50 kilowatts (kW) – using a laser at the High Energy Laser Systems Test Facility (HELSTF), operated by the U.S. Army and located in New Mexico. By comparison, a 5-kW laser beam can cut through an inch of steel. Traditional techniques for gauging laser power require using an apparatus to absorb all the energy from the beam as heat. Measuring the temperature change allows researchers to calculate the laser’s power.
But with very high laser powers, this conventional method becomes tricky to implement. If the instrument is not properly cooled, it could be destroyed by the laser beam that it is supposed to measure. Instead of acting as a heat sink, NIST’s RPPM works by measuring the pressure of laser light on a mirror.