Simple optical knife-edge effect based motion detection approach for a microcantilever

Abstract

Here, we describe a simple optical motion detection method for a microcantilever by positioning a microcantilever in front of a photodetector and focusing a light to the side of the cantilever in the in-plane direction. The out-of-plane vibration of the microcantilever, acting as an knife-edge itself, modulates the amount of light reaching the photodetector, allowing the alternate motion detection scheme. The method presented offers the optical responsivity around 0.3 mW/μm, which is high enough to observe the thermomechanical fluctuations of a microcantilever in order of a few pm/Hz. The demonstrated detection scheme can reduce the complexity and the relative size of the detection configuration, often required in the conventional methods, and would be useful as a complementary technique to existing ones.