Multiple reflection assisted Laser Doppler Vibrometer setup for high resolution displacement measurement

TL;DR

This paper presents a high-resolution, non-intrusive laser Doppler vibrometer setup that uses multiple reflections within a high-Q cavity to enhance displacement measurement resolution beyond traditional limits.

Contribution

The authors introduce a novel LDV-based displacement sensor utilizing multiple reflections to significantly improve measurement resolution beyond λ/4.

Findings

Achieved 72 nm displacement measurement with ±14 nm error

Resolution enhancement through phase multiplication in a high-Q cavity

Measurement mainly limited by reflectivity and physical dimensions

Abstract

Non-intrusive displacement measurement technique has a distinct edge over displacement sensors working in contact mode. Laser Doppler Vibrometry based schemes (LDV) offer such an advantage. However, the measurements are limited up to $\lambda/4$, where $\lambda$ is the wavelength of optical source. An experimental design of high resolution non-intrusive displacement sensor working on the principle of basic LDV is being presented here. Resolution enhancement has been achieved through phase multiplication using multiple reflections within a high-Q cavity created by a vibrating surface and a high reflection mirror kept parallel to each other. Displacement of 72 $nm$ has been measured with an error range of $\pm 14$ $nm$ through direct counting of characteristic peaks in "half cycle" of the interferogram. The experimental design offers a straightforward route to measure displacement and the measurement resolution is mainly limited by the reflectivity and physical dimension of moving source.