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noisy projected image with DMD

ewc
Prodigy 40 points
Other Parts Discussed in Thread: DLP7000

Hi all,

I'm using a DLP7000 in an imaging application. I direct a 470nm, coherent laser source onto the DLP7000, and project an image of the DMD onto my sample. My setup just uses a single lens, for focusing the image. However what I find is that the image I obtain is somewhat noisy: 

[Image of obtained pattern from "Zhu et al. (2012) Nature Protocols"]

Is the noise in the projected image due to diffraction of the light from the DMD? What are the possible ways to reduce this noise?

Thank you!

  • 0
    TI__Guru 54705 points

    Hello EWC,

    Thank for the diagram it is helpful.  We do need a little more information that was not part of the drawing. 

    Please tell us about the illumination light:

    • Beam expander
    • Collimated?  If not what is the F#?
    • Uniformity.  Are you filling the entire DMD or just a portion? 
    • if only a portion, what is the shape and intensity profile?
    • if the whole DMD what is the variation in intensity across the DMD array?

    Please tell us more about the projection side?

    • What is the F# of the projection lens

    Thank you,

    Fizix

  • 0 in reply to Fizix
    Prodigy 40 points

    Hi Fizix,

    I'm projecting my laser beam directly onto the DMD without any optics in between, no beam expansion at all. Therefore I'm just filling a tiny portion of the DMD (~2mm width). The beam operates near TEM01 (edited).

    On the projection side, the projection lens is f/2.

    Thank you!

    -Edmund

  • 0 in reply to ewc
    TI__Guru 54705 points

    Hello Edmund,

    Does the portion of the DMD that you are illuminating contain the entire pattern that you are attempting to project onto the screen?

    I do not think this is being driven by the diffraction.  Diffraction only limits the rays to specific directions but the rays are not extraordinary rays and should follow geometric optics in the lens.

    You may want to try a beam expander and/or a lens to make the effective illumination NA larger.  Please let me know the result if you try this.

    Fizix