# Simultanous two-wavelength phase unwrapping using external module for multiplexing off-axis holography

## TL;DR

This paper introduces a dual-wavelength external holographic microscopy system that captures two interferograms simultaneously to enable phase unwrapping over extended thickness ranges in 3D imaging.

## Contribution

It presents a novel optical multiplexing approach for simultaneous dual-wavelength interferogram acquisition in off-axis holography.

## Key findings

- Successfully imaged a 7.96 μm step target.
- Quantitatively imaged 30.5 μm copper pillars.
- Extended the measurable thickness range in 3D phase imaging.

## Abstract

We present a dual-wavelength external holographic microscopy module for quantitative phase imaging of 3D structures with extended thickness range. This is done by simultaneous acquisition of two off-axis interferograms, each of which at a different wavelength, and generation of a synthetic wavelength, which is larger than the sample optical thickness, allowing two-wavelength unwrapping. The simultaneous acquisition is carried out by using optical multiplexing of the two interferograms onto the camera, where each of them has orthogonal off-axis interference fringe direction in relation to the other one. We used the system to quantitatively image a 7.96 um step target and 30.5 um circular copper pillars.

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Source: https://tomesphere.com/paper/1904.01445