# Extended Depth-range Dual-wavelength Interferometry Based on Iterative Two-step Temporal Phase-unwrapping

## TL;DR

This paper introduces an advanced dual-wavelength interferometry method that extends depth-range and enhances sensitivity by using iterative two-step temporal phase-unwrapping with a least squares approach on phase-shifting interferograms.

## Contribution

It proposes a novel extended depth-range dual-wavelength phase-shifting interferometry technique that improves phase unwrapping accuracy and sensitivity over previous methods.

## Key findings

- Demonstrates high precision in simulated experiments
- Extends depth-range effectively
- Improves sensitivity in phase retrieval

## Abstract

Phase retrieval is one of the most challenging processes in many interferometry techniques. To promote the phase retrieval, Xu et. al [X. Xu, Y. Wang, Y. Xu, W. Jin. 2016] proposed a method based on dual-wavelength interferometry. However, the phase-difference brings large noise due to its low sensitivity and signal-to-noise ratio (SNR). Beside, special phase shifts are required in Xu's method. In the light of these problems, an extended depth-range dual-wavelength phase-shifting interferometry is proposed. Firstly, the least squares algorithm is utilized to retrieve the single-wavelength phase from a sequence of N-frame simultaneous phase-shifting dual-wavelength interferograms (SPSDWI) with random phase shifts. Then the phase-difference and phase-sum are calculated from the wrapped phases of single wavelength, and the iterative two-step temporal phase-unwrapping is introduced to unwrap the phase-sum, which can extend the depth-range and improve the sensitivity. Finally, the height of objects is achieved. Simulated experiments are conducted to demonstrate the superb precision and overall performance of the proposed method.

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Source: https://tomesphere.com/paper/1704.08139