Created by admin on 08/04/2025

Tutorials Digital holography

ZoomFFT for speeding up off-axis computation (and more)

Github DOI

When performing the computation for some tasks such as off-axis holography, we often have to compute the entire FFT of a signal or an image while being only interested in a very small part of the spectrum. The rest of the information is just discarded. While the FFT algorithm and its implementation in standard computing libraries are very efficient, we can still take advantage of a slower approach which only computes what we need. The ZoomFFT algorithm does just that! And it's already available in standard packages such as SciPy for Python or in MATLAB. Using off-axis holography as an example, I will show how to save time – or not – using ZoomFFT.

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Created by sebastien.popoff on 01/07/2024

Tutorials Spatial Light Modulators

A practical guide to Digital Micro-mirror Devices (DMDs) for wavefront shaping

 

Sébastien M Popoff1 , Louis Malosse2 , Rodrigo Gutiérrez-Cuevas1 , Yaron Bromberg3 , Jean Commère2 , Marie Glanc2, Raphaël Galicher2, and Maxime W Matthés1

Citation Badge ArXiv Github

 

Digital micromirror devices have gained popularity in wavefront shaping,  offering a high frame rate alternative to liquid crystal spatial light modulators. They are relatively inexpensive, offer high resolution, are easy to operate, and a single device can be used in a broad optical bandwidth. However, some technical drawbacks must be considered to achieve optimal performance. These issues, often undocumented by manufacturers, mostly stem from the device's original design for video projection applications. Herein, we present a guide to characterize and mitigate these effects. Our focus is on providing simple and practical solutions that can be easily incorporated into a typical wavefront shaping setup.

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DMD

Created by sebastien.popoff on 16/12/2022

Tutorials Highlights

Compensating for phase drifts in holographic measurements

Red dot

Digital holography allows measuring the complex amplitude of a given wavefront. We presented in detail the off-axis holography approach. However, it requires a separate reference arm. Due to air flow, vibrations, or other perturbations, the optical path length difference between the two arms can fluctuate in time, even in controlled lab experiments on a good optical table. This means that the phase of the measured wavefront is estimated up to a global phase that can randomly change over time. This is very detrimental for transmission matrix measurements as the relative phase between each column has to be precisely estimated. This is particularly true when the measurement time can take few minutes or more when using a liquid crystal spatial light modulator that has a limited frame rate. In [R. Mouthaan et al., Appl. Opt. (2022)], the authors propose a simple yet robust way to compensate for phase fluctuations, even when the phase changes completely between two frames.

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Created by sebastien.popoff on 01/10/2021

Talks Tutorials Others

Spatiotemporal control of light

Joel A. Carpenter
October 2021

Gerchberg-Saxton is a phase retrieval algorithm, which attempts to retrieve the phase corresponding to two intensity images taken in the near and far-field respectively. It can also be used for calculating computer-generated holograms (phase masks) that generate a desired.

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