Photothermal measurements at picowatt resolution using uncooled micro-optomechanical sensors

Abstract
Deflections of bimaterial microcantilever beams were optically detected with 400 fm resolution at room temperature. This enabled photothermal radiation detection with resolutions of 40 pW for power and 10 fJ for energy. The resolution was improved by an order of magnitude by optimizing the thickness ratio of the two beam materials, as well as by modulating the incident radiation at sufficiently high frequency to be in the range of the thermal white noise limit of the cantilever vibrations. Radiative power was detected with a noise spectral density of and 250 pW/Hz and detectivity, D*, of 4.6×107 cm Hz/W.