Here Am I

 

Hi, I'm Pi. In this blog, I will present some of my work done at home that is related to physics. Feel free to ask questions if you are interested in some of the work.

The first post will be about the first experiment that I did at home, and this was the making of an SLM (spatial light modulator) from a conventional projector.

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Project CD (a very old project, still ongoing)

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 You may be wondering why I'm interested in SLM or computer-generated holograms (CGH). Why all this? The answer is somehow complicated, but it all started many, many years ago. There was an article in the news that some scientist wrote a hologram on a CD (compact disc - if you know what it is ;). When I heard about this news I thought maybe I should try to make it also, and project CD was born (originally called CD project but I think I can not use this name ;( ). The idea was simple - write a hologram on a CD. It took some time but I managed to write something visible on a CD (on the data side). Then I started to read de documentation of a compact disc and tried to overcome all protection of data on the CD. After a long time, I managed to write a picture. Then I forgot about the project and lost all programs that I wrote for it. After some time I started again. With some background on what works and what doesn't. Eventually, I made the same progress as before (but I think the
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CGH (computer generated hologram)

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At the beginning, what does a simple CGH look like:             It's been a while since the last entry, nevertheless today I will present some work that I did one month ago. For the first time I tried to make my own calculation of a hologram. It was an easy approach, first a simple phase hologram, where you take only the phase of the light recorded on a real hologram. The results were not that good (I didn't take a photo of it, but there was not much to see). Then I started with a more complicated algorithm, but still very simple CGH (computer generated hologram) - IFTA (Iterative Fourier Transform Algorithm) also known as Gerchberg-Saxton algorithm. The results were somehow better but still some work has to be done. The input picture is shown in fig2 -a very simple image.   After feeding it to the program that I wrote in python I got three outputs, first how does the picture look after 200 iterations of the program. Since IFTA is an iteration algorithm with each iteration the
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SLM (spatial light modulator) made from a projector.

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SLM is a very interesting device. It modulates light in space, either modulating the phase or the amplitude of light. There are plenty of uses for an SLM (search in Wikipedia). The main goal of the post is to show such a device made from an ordinary video projector. There are scientific papers on how to do that (search for example "A low-cost spatial light modulator for use in undergraduate and graduate optics labs") I made my SLM some years ago, and now is the time to use it. It was made from an old LCD projector shown in photo 1 (ASK C90) it is old and dusty but it works. I removed the light bulb and I so changed the control circuit that it thinks that the light bulb is on. I took out the LCD modules (there are three for each RGB color, so three SLM :) I bought extension cables to connect the LCD module to the device (photo 2), and I made a hole in the projector so that I could connect the LCD module outside the device. We shine a laser on the LCD module and that's all
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