Autodyne measurements of micro and nano vibrations by the low-frequency spectrum of diode laser

The research results of autodyne signal formed under reflection of semiconductor laser radiation from vibrating reflector have been presented. The influence of feedback coefficient and distance to vibrating object on an autodyne signal form has been shown. The method of reverse problem solution in autodyne interferometry of nonharmonical vibrations has been described. The suggested method allows us to restore the amplitude and form of mechanical vibrations for autodyne system developed for interference system separated from the light source. A method of amplitude determination of mechanical vibrations from the spectrum of autodyne signal of semiconductor laser is described. The relation between the vibration amplitude of an object and the frequency of spectral component with the maximum amplitude in the spectrum of the autodyne signal has been obtained. The least-squares method was used to obtain the approximation coefficient. Measurements of vibration of micron amplitude of piezoelectric plate were carried out with the help of a semiconductor laser autodyne system. A method for the quantitative monitoring of nanometer vibrations based on the autodyne detection effect in a semiconductor laser has been developed. It is shown that the semiconductor laser autodyne can be used for measuring vibration amplitudes in the range from one nanometer to 10 mum in the frequency band from a few hertz to several hundred megahertz. With the aid of a lock-in amplifier, the lower threshold of measured vibration amplitudes has been reduced to one angstrom.