Created by sebastien.popoff on 21/09/2018

Tutorials Spatial Light Modulators

How to calibrate linearly aligned nematic liquid crystal based SLMs

 

I previously posted a tutorial presenting a technique to calibrate spatial light modulators (SLMs). The approach was based on measuring the interference between two paths that have been reflected off two different regions of the SLM. This technique is always valid but requires aligning a mask, using a lens, and capturing and processing images of interference patterns. Nowadays, most phase-only SLMs based on liquid crystals use linearly aligned nematic crystals. Unlike twisted nematic liquid crystals, they allow phase-only modulation on one polarization while not affecting the orthogonal polarization. This feature can be used to simplify the calibration setup to characterize the SLM with a common path interferometer, not requiring a precise alignment [1]. Furthermore, it only needs a photo-detector, compared to a digital camera in the previously presented approach. This is convenient to measure the inevitable phase fluctuations of an SLM, usually around a 100 to 400 Hz frequency. In this document, we briefly describe the principle of the characterization scheme as presented in [2] and show typical results of the calibration and phase fluctuations.

Written by Paul Balondrade and Sébastien M. Popoff

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Created by sebastien.popoff on 29/10/2016

Tutorials Spatial Light Modulators

Setting up a DMD: Diffraction effects

I recently acquired a Digital Micromirror Device (DMD) and when I started setting up the experiment, I faced a problem I did not anticipate which is closely related to blazed gratings. Due to the fact that the surface of a DMD is not flat, diffraction orders are shifted compared to the optical axis. This shift depends on the pixel pitch, the wavelength, and the incident angle. A close look at this diffraction phenomenon is important to configure an experimental setup properly. It is even relevant to consider this effect before choosing the appropriate DMD model to buy.

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Created by sebastien.popoff on 17/10/2016

Tutorials Spatial Light Modulators

Control a Vialux DMD with Python

Vialux provides Texas Instrument DMD (Digital MicroMirror Devices) chips with an electronic board to send and display image sequences at high speed (up to 30kHz). While they provide a C++ dll, Labview, and Matlab codes, I did not find any tool for Python. I share here a simple module that wraps the C++ functions for Python. It allows using in a simple manner the basic functions while providing the advanced features of the ALP API.

DOI

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Created by sebastien.popoff on 09/10/2016

Tutorials Spatial Light Modulators

Easy generation of Laguerre Gauss beam with Python and an SLM

I want to share a simple Python written by José Salazar-Serrano. This program aims to generate a Laguerre Gauss beam with a phase-only spatial light modulator (SLM). It uses the slmPy and requires the wxPython and opencv modules to run. The full description of the package and the files are available on the Github repository.

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