Direct measurement of radiation pressure and circulating power inside a passive optical cavity

Microfabricated sensor device for CW and pulsed laser power measurements

On-line measurement is a trend of development toward laser-based applications. We present a fiber-integrated force sensor device for laser power measurement with both CW mode and pulse mode based on laser radiometric heat and radiation force sensing simultaneously. The sensor device is fabricated using a standard microfabrication process. Laser intensity is determined through the displacement of a movable mirror measured by an integrated Fabry-Perot interferometer. Compared with the performance of the device in the ambient condition, a non-linearity error of 0.02% and measurement uncertainty of 2.06% is observed in the quasi-vacuum condition for CW laser illumination. This device can measure a CW laser power with a 46.4 μW/Hz^1/2 noise floor and a minimum detection limit of 0.125 mW. For a pulsed laser, a non-linearity error of 0.37% and measurement uncertainty of 2.08% is achieved with a noise floor of 1.3 μJ/Hz^1/2 and a minimum detection limit of 3 μJ.

High amplification laser-pressure optic enables ultra-low uncertainty measurements of the optical laser power at kilowatt levels

We present the first measurements of kilowatt laser power with an uncertainty less than 1 %. These represent progress toward the most accurate measurements of laser power above 1 kW at 1070 nm wavelength and establish a more precise link between force metrology and laser power metrology. Radiation pressure, or photon momentum, is a relatively new method of non-destructively measuring laser power. We demonstrate how a multiple reflection optical system amplifies the pressure of a kilowatt class laser incoherently to improve the signal to noise ratio in a radiation pressure-based measurement. With 14 incoherent reflections of the laser, we measure a total uncertainty of 0.26 % for an input power of 10 kW and 0.46 % for an input power of 1 kW at the 95 % confidence level. These measurements of absolute power are traceable to the SI kilogram and mark a state-of-the-art improvement in measurement precision by a factor of four.

Radiation pressure measurement using a macroscopic oscillator in an ambient environment

In contrast to current efforts to quantify the radiation pressure of light using nano-micromechanical resonators in cryogenic conditions, we proposed and experimentally demonstrated the radiation pressure measurement in ambient conditions by utilizing a macroscopic mechanical longitudinal oscillator with an effective mass of the order of 20 g. The light pressure on a mirror attached to the oscillator was recorded in a Michelson interferometer and results showed, within the experimental accuracy of 3.9%, a good agreement with the harmonic oscillator model without free parameters.

Miniature force sensor for absolute laser power measurements via radiation pressure at hundreds of watts

We present a small power meter that detects the radiation pressure of an incident high-power laser. Given its small package and non-destructive interaction with the laser, this power meter is well suited to realizing a robust real-time, high-accuracy power measurement in laser-based manufacturing environments. The incident laser power is determined through interferometric measurement of displacement of a 20 mm diameter high reflectivity mirror, mounted at the center of a dual element spiral flexure. This device can measure laser power from 25 W to 400 W with a 260 m W/H z noise floor and ≤ 3.2% expanded uncertainty. We validate our device against a calibrated thermopile with simultaneous measurements of an unpolarized 1070 nm laser and report good agreement between the two systems. Finally, by referencing to an identical mechanical spring that does not see the incident laser, we suppress vibration noise in the power measurement by 14.8 dB over a 600 Hz measured bandwidth. This is an improvement over other radiation pressure based power meters that have previously been demonstrated.