Optically Excited And Interrogated Micromechanical Silicon Cantilever Structure

Micromechanical silicon cantilever structures of typical dimensions 1 mm x 80 μm x 5 μm have been excited by absorption of pulsed light from diode laser at 790 nm or a LED at 830 nm respectively. The excitation motion of the cantilevers was measured by means of a fiber-optic Michelson interferometer as well as a reflective multimode fiber optic pick up. In addition to the optical signal the electrical signal of a thin film piezoresistive transducer localized at the base of the cantilever has been measured. The optimal fiber position with respect to the cantilever was determined experimentally. At this position a signal to noise ratio of about 6 could be realized for the detected signal at 5 kHz bandwidth for optical power levels of 56 pW. Using a 125 μm diameter optical fiber this corresponds to an optical power density of 4.6 mW/mm2 which is below the critical value of 5 mW/mm2 suggested for explosive environments.