I am studying the possibility to use the dmd for a confocal microscope. A big issue for me at the moment is the diffraction pattern I am obtaining in the detector, superimposed to the object image. Are there solutions to overcome this problem?
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Could you give more detail on what your setup is and what you are seeing? Diffraction is a physical property of the geometrically repetitive structures of the DMD and the wave properties of light. However, there may be architectural considerations which can minimize the effects. I can't offer anything specific until I know your arrangement in more detail.
thank you for your reply.
The system we are evaluating at the moment uses an LED source (and not a laser) without polarization (I guess it would be needed, but we would not want to move towards a laser source, anyway).
The incident angle is 24 degrees with respect to the dmd "0 state", in order to use the "on" state to send light parallel to the dmd axis. At the moment the illumination path creates a converging beam to the dmd (probably a parallel one would be better, I guess). Then there is a tube lens infinite conjugate and the microscope objective.
A displaced mirror actually acts as spatial beam splitter and reflects the light in the imaging path. I am experiencing - at the moment - that the sample creates a pattern after the imaging lenses when is located at the confocal distance. I am introducing a mask in the imaging path to spatially remove all the light but the one due to the sample. However, of course, even the backscattered /refracted light coming from the dmd itself is partially allowed to reach the ccd.
If this problem does not affect the image when I need a very low level of light in the sample, it becomes very critical when I need to go inside the sample itself (I am dealing with human cells). My samples, in fact, have very low level of diffusion, so they are a bit a nightmare ...
I am pretty sure the undesired light is coming from the dmd because I can detect it even when no samples are placed after the objective, and even when I completely remove the tubelens and the objective.
Thank you and regards
Thank you for the response and description of your system. I'm afraid that I can't tell from this level of detail how to address your question. It is probably necessary to see a diagram or optical layout with distances, stops, shielding, etc. to evaluate your system. There is some diffractive scattering from a DMD, but the details depend on many factors, primarily optical path - both illumination side and collection side.
I can make it possible for you to establish a private link with me so that you may feel more free to give details. I'm sending you a Friend request, which will allow us to have a private conversation.
I am trying to build the same system that Michele built, DMD based confocal microscope for biological application too, but I am having troubles getting the diffraction pattern through the tube lens. I used a pair of lenses in order to shrink the image and to fit it to the back of the objective but it did not work. Can you please send me a Friend request ? I would like to chat with you about it.
I have sent you a friend request.
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