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Optical Power Meter

Patent Number: 9,625,313


A metal cube (RPPM) mounted on a metal surface has round holes cut in each side.
Credit: NIST
A NIST RPPM unit: Laser beam enters though one portal and exits through another after being reflected from a mirrored surface inside.

NIST scientists have devised a radically new method of determining laser power by measuring the radiation pressure exerted by a laser beam on a reflective surface.

High-accuracy power measurements are essential to many manufacturing processes that depend on precise control of laser output. Conventional techniques for gauging laser power involve aiming the beam into an apparatus that absorbs all the beam’s energy as heat. The change in temperature is a measure of power. 

But this method requires the laser to be taken out of service during calibration, preventing precision measurement of the laser’s power while it is in use, leading to potential inconsistencies. Without this information, some manufacturers may have to spend more time and money assessing whether their parts meet manufacturing specifications after production. Moreover, instruments that can support high-power measurements are large and require significant operating infrastructure. 

Power measurements while lasers are at work on the factory floor

By contrast, the compact NIST Radiation Pressure Power Meter (RPPM) gauges the power of a laser beam by measuring how much the beam’s radiation pressure displaces a mirrored surface: The greater the displacement, the larger the beam force and thus the higher the power. Because the beam is reflected, not absorbed, it proceeds to its application on a production line as measurements are made.

Wide power range, easily integrated into manufacturing operations.


  • Real-time measurement does not interrupt laser use
  • Measurements up to 500 kW with well-quantified uncertainty
  • Components customizable for different laser frequencies and power
  • Faster measurements than conventional technology
  • Simplified power scalability
  • Provided by NIST as a Standard Reference Instrument available for purchase


  • Laser cutting
  • Laser welding
  • 3D printing
  • Robotic lasers
  • Directed energy weapons


The RPPM is extremely well suited to industries — such as ship, automotive, and aircraft fabrication and assembly — that make use of precision laser cutting and welding, as well as the use of robotic lasers in automotive manufacture.

Created March 24, 2020, Updated April 6, 2020