Micromachined force scale for optical power measurement by radiation pressure sensing

TL;DR

This paper presents a novel micromachined force scale that measures laser power via radiation pressure without absorption, enabling fast, in-line laser monitoring with a compact silicon device.

Contribution

It introduces a silicon micromachined force sensor for optical power measurement based on radiation pressure, with a nulling electrostatic force technique and demonstrated fast response.

Findings

Response time less than 20 ms

Noise floor at 2.5 W/√Hz

Operates with 250 W laser in open-loop

Abstract

We introduce a micromachined force scale for laser power measurement by means of radiation pressure sensing. With this technique, the measured laser light is not absorbed and can be utilized while being measured. We employ silicon micromachining technology to construct a miniature force scale, opening the potential to its use for fast in-line laser process monitoring. Here we describe the mechanical sensing principle and conversion to an electrical signal. We further outline an electrostatic force substitution process for nulling of the radiation pressure force on the sensor mirror. Finally, we look at the performance of a proof-of-concept device in open-loop operation (without the nulling electrostatic force) subjected to a modulated laser at 250 W and find its response time is less than 20 ms with noise floor dominated by electronics at 2.5 W/root(Hz).