Optically excited mechanical vibrations in micromachined silicon cantilever structures

Mechanical vibrations in micromachined silicon cantilever structures with typical dimensions of 1000x80x5 micro cubicmeters by the local absorption of pulsed laser light at 780 nm or LED light at 830 nm respectively. The motion of the cantilevers could be detected with a fiber-optic Michelson interferometer and a reflective multimode fiber optic pick-up system. In addition, the cantilever deflection could be measured with a poly-silicon-piezoresistor located at the base of the silicon beam. At the experimentally determined optimal fiber position a signal to noise ratio of about 6 could be realized for the detected signal at a bandwidth of 5 kHz and optical power levels of 56 myW. Using an optical fiber with 125 mym diameter the optical power density is well below the value of 5 mW/square millimeter suggested for explosive environments. (IMT)