Characterization of a 10-MHz quadrant APD for measuring frequency oscillations and tip displacements of microcantilevers

Abstract

The room-temperature response of a 10-MHz quadrant avalanche photodiode (APD) is investigated for detection of high frequency oscillations and tip displacements of fabricated microcantilevers. Currently, no quadrant detectors with a response bandwidth in the megahertz range are available, and oscillations on the order of a few microseconds cannot be resolved. A comparison is made between optical and opto-mechanical measurements to characterize this detector by investigating the frequency response and signal-to-noise (SNR) of pulsed laser signals up to 10 MHz and reflected laser signals from freely vibrating microcantilevers up to 1.64 MHz. The power level of the minimum detectable signal incident on the APD is found to be 28.2 ± 5.0 nW for optical measurements and 1.0 μW ± 5.0 nW for opto-mechanical measurements.