Temperature measurement on MOEMS micromirror plates under illumination

Abstract

The Fraunhofer Institute for Photonic Microsystems (IPMS) develops and fabricates MOEMS micro-mirror arrays for a variety of applications in image generation, wave-front correction and pulse shaping. In an effort to extent the application range, mirrors are being developed that withstand higher light intensities. The absorbed light generates heat. Being suspended on thin hinges, and isolated from the bulk by an air gap, the mirrors heat up. Their temperature can be significantly higher than that of their substrate. In this paper we describe an experiment carried out to verify simulations on the temperature within the mirror plates during irradiation. We created a structure out of electrically connected mirror plates forming a four-point electrical resistor, and calibrated the thermal coefficient of the resistor in a temperature chamber. We irradiated the resistor and calculated the mirror temperature. In the experiment, the temperature in the mirror plates increased by up to 180 °C. The mirrors did not show significant damage despite the high temperatures. Also, the experiment confirms the choice of heat transport mechanisms used in the simulations. The experiment was done on 48 ?m x 48 ?m mirrors suspended over a 5 ?m air gap, using a 355 nm solid-state laser (4 W, up to 500 W/cm²)