Full-dynamic phase modulator for heterodyne interferometric vibration measurements

A novel full-dynamic phase-demodulator for heterodyne interferometric vibration measurements is described. Contrary to a conventional phase-demodulator, which has a limited dynamic range of +/- 90 degree(s), the proposed phase- demodulator has an unlimited dynamic range. This allows to recover phase information for displacements of the surface under test which are much greater than the wavelength of light. Noise measurements of the demodulator show that, for a carrier-to-noise ratio of 70 dB within 3 kHz bandwidth, a phase noise of less than 3 (mu) rad/(root)Hz can be expected. Finally, a digital version of the full-dynamic phase- demodulator with an extended frequency response has been developed. The comparison between the analog and digital phase-demodulator versions is discussed and examples of phase recovery are presented.