ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
We describe an energy transfer process whereby a moving particle loses (or gains) kinetic energy upon interacting with the moving optical potential of a swept beam of light. This approach is akin to a gravitational assist maneuver for interplanetary satellite propulsion. Special consideration is given to the stopping condition. For analytical convenience, we examine the Rayleigh scattering regime, providing examples at small and large scattering angles. A 5% uncertainty in the initial particle speed and position has negligible effect on the slowing/speeding ability when the beam size is much larger than the particle.
ABSTRACT
The intensity-dependent rocking frequency of an illuminated semicylindrical refractive rod (or "optical wing") on a flat, nonslip surface is investigated. Both longitudinal and transverse radiation pressure forces (scatter and lift forces), as well as radiation pressure torque, transform the mechanical system into one having a bistable potential energy above a critical intensity. The equation of motion may be written as a parametrically driven nonlinear bistable harmonic oscillator, resulting in complex rocking dynamics. The effects of linear and sinusoidal intensity modulation schemes are explored, and experimental conditions to verify these results are discussed.
ABSTRACT
An optical wing is a cambered rod that experiences a force and torque owing to the reflection and transmission of light from the surface. Here we address how such a wing may be designed to maintain an efficient thrust from radiation pressure (RP) while also providing a torque that returns the wing to a source facing orientation. The torsional stiffness of two different wing cross-sections is determined from numerical ray-tracing analyses. These results demonstrate the potential to construct a passive sun-tracking, space flight system or a microscopic surface measurement device based on RP force and torque.
