Holographic interferometer sensitivity estimation in optical measurements

Abstract

Interferometers used for high-precision spectroscopic measurements are considered. The choice of a holographic interferometer is supported because of it implements the spatial-spectral method of holographic interferometry. With this holographic interferometer one can measure in real time the displacements of the phase center of a coherent light flux over a wide dynamic range and record the measured data in digital form. Based on the mathematical relations elucidated by the authors in previous publications, and based on the results of experimental studies, we have been able to numerically estimate the sensitivity of a holographic interferometer to spatial movements of phase centers (focus points) of light fluxes—point light sources that form a holographic interferogram. We establish the dependence of the normalized level of light flux intensity in the central region of the holographic interferogram on the displacement of a real point light source along the normal to the plane of the Fourier hologram. From the results of mathematical simulation we show that the sensitivity of a holographic interferometer to the movements of a real point light source normal to the plane of the Fourier hologram depends on the optical circuit parameters of the holographic interferometer when exposing the hologram and on the measurement parameters. In this case, the sensitivity of a holographic interferometer to specific movements of a real point light source can only be estimated experimentally. We propose to increase the sensitivity of a holographic interferometer by using a thin converging lens in its optical design. A mathematical relation has been obtained and studied for the gain coefficient of the phase advance of a light flux with a spherical wavefront. Given the known parameters of the thin converging lens in the optical circuit, we can use this relationship to numerically estimate the increase in sensitivity of a holographic interferometer that implements the spatial-spectral method of holographic interferometry. It is shown that the sensitivity of the holographic interferometer to the displacement of an imaginary point light source normal to the plane of the Fourier hologram is 2.86 times greater than its sensitivity to the same movement of a real point light source. It has been established that the sensitivity of holographic interferometer with a volumetric Fourier hologram and a thin converging lens in its design can be increased by no less than an order of magnitude compared with the sensitivity of known optical interferometers. The results of assessing the sensitivity of the holographic interferometer implementing the spatial-spectral method of holographic interferometry to displacement of point sources of real and imaginary light fluxes, as well as the resulting ratio for the gain coefficient of the phase advance of the light flux by the thin converging lens, will be useful for high-precision measurements of linear and angular movement of objects, as well as in the construction of photonic device structures. From the results of the study based on the holographic interferometer, an experimental sample of an acousto-electric transducer has been developed and manufactured, which has high sensitivity over wide dynamic and frequency ranges and is intended for use in acoustic locations of unmanned aerial vehicles.