Measuring vibrational frequency of vibratable pins

摘要

Measuring vibrational frequency of a pin attached at one end by collimating two laser beams onto the pin and back scattering the beams. The back scattered frequency is modulated by doppler effect and is heterodyned with the original beam frequency to produce a signal representative of each modulating frequency. The representative signals are summed together and also subtracted from one another. The summed and subtracted signals are representative, one of the vibrational frequency of the pin and the other of the degree of focussing accuracy of each laser beam onto the pin.