Optical and infrared detection using microcantilevers

The feasibility of micromechanical optical and infrared (IR) detection using microcantilevers is demonstrated. Microcantilevers provide a simple means for developing single- and multi-element sensors for visible and infrared radiation that are smaller, more sensitive and lower in cost than quantum or thermal detectors. Microcantilevers coated with a heat absorbing layer undergo bending due to the differential stress originating from the bimetallic effect. Bending is proportional to the amount of heat absorbed and can be detected using optical or electrical methods such as resistance changes in piezoresistive cantilevers. The microcantilever sensors exhibit two distinct thermal responses: a fast one (τ₁^thermal less than ms) and a slower one (τ₂^thermal approximately 10 ms). A noise equivalent temperature difference, NEDT equals 90 mK was measured. When uncoated microcantilevers were irradiated by a low-power diode laser (λ equals 786 nm) the noise equivalent power, NEP, was found to be 3.5 nW/√Hz which corresponds to a specific detectivity, D*, of 3.6 multiplied by 10⁷ cm · √Hz/W at a modulation frequency of 20 Hz.