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Inline Laser Power Measurement by Photon Momentum



John H. Lehman, Paul A. Williams, Daniel W. Rahn, Kyle A. Rogers


We present a measurement scheme and instrumentation for quantifying laser power by means of photon momentum. The optical design is optimized such that the incoming laser beam is minimally perturbed and is available for other purposes along the incoming beam axis. Additionally, the geometry of the instrument gives access to the small but measurable transmittance between two passive mirrors that face the force sensor. The force sensor is based on a commercially available weighing instrument (“scale”) that has a temporal response of approximately 5 sec and a readability of approximately 1 µg (~2 W). Our measurement results are shown for 500 W, but the mirror and mass (or force) calibration are suitable for very high power up to 50 kW and beyond. The optics are based on commercially available, off-the-shelf mirrors optimized for the angle of incidence and maximum reflectance at the wavelength of 1070 nm. The size of the complete instrument has an input aperture of ø75 mm, but this constraint is only a matter of optimizing the beam path and box geometry.
Applied Optics


Radiation Pressure, Photon Momentum, Laser Power, kilogram


Lehman, J. , Williams, P. , Rahn, D. and Rogers, K. (2019), Inline Laser Power Measurement by Photon Momentum, Applied Optics, [online], (Accessed April 20, 2024)
Created February 6, 2019, Updated February 5, 2019