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DLP7000: Expected Diffraction Efficiency At Blazed Wavelength ?

Maximilian Hoffmann
Prodigy 40 points
Part Number: DLP7000
Other Parts Discussed in Thread: DLP4500NIR

Dear Community/Support,

I have a DLP700 with a pixel pitch of 13.7 µm. This should meet the blazing condition at around 820 nm for an incident angle of 0 degree. 

Indeed if I vary the wavelength this seems to be the sweet spot around that area, however the efficiency is only around 60%. This is not an NIR DMD, but the one-pass transmittance of Corning 7056 is still given as 0.9 or so. 

Is this expected? If so, what explains the low efficiency at this rather high fill-factor, if the theoretical efficiency of blazed grating should be around 100%.

Best

  • 0
    TI__Guru 54555 points

    Hello Maximilian,

    Unfortunately what you are seeing is not a diffraction effect at all.  The micro-mirrors are basically aluminum.  The reflectivity of aluminum has a local minimum around 820-830 nm which dips to around 86%.  

    Further, even for a blazed order the theoretical diffraction efficiency of a DMD array (fill factor included) is around 90%.  The reflectivity coupled with two passes through the window (transmittance) and diffraction efficiency will result in a throughput around 60%.

    So the answer is, yes, this is expected.

    Fizix

  • 0 in reply to Fizix
    Prodigy 40 points
    Thank you for your answer, of course the Aluminum....
    Is there a possibility to get an NIR-AR coating on the DLP7000?
    Is there any DMD device, which has better reflectance specs, maybe Silver or the like?
  • 0 in reply to Maximilian Hoffmann
    TI__Guru 54555 points

    Max,

    Regarding the micro-mirror material, the answer is we only manufacture aluminum ones.

    We do have a DLP4500NIR, which is a "diamond pixel" device.  It is a smaller pixel (7.6 µm), so you would have to do the diffraction calculations for the smaller mirror pitch.

    Fizix

  • 0 in reply to Fizix
    Prodigy 40 points

    Thanks, for your answer. I was aware of the NIR DMD. Unfortunately it's pitch is prohibitive for my application + the 32kHz speed is important.
    Is there any way to obtain a custom made window for the DLP7000?

  • 0 in reply to Maximilian Hoffmann
    TI__Guru 54555 points
    Hello Max,

    I hadn't done the calculation, but I suspected that the pixel pitch might cause an "anti-blaze" condition at this wavelength.
  • 0 in reply to Fizix
    Prodigy 40 points

    Hi,

    and are they any custom window coatings?

    Would you share the Corning 7056 transmittance values as a csv file or the like?

    Thank you

  • 0 in reply to Maximilian Hoffmann
    TI__Guru 54555 points

    Hello Maximilian,

    There are no custom windows for the DLP7000 other than the UV an VIS that we make.

    Regarding the window transmission, we have persmission from Corning to publish the graphs of the AR coating thay apply as shown in the Window Transmission White Paper, but we do not publish the raw data.

    Fizix

    P.S.  Sorry for the delay, I have been on vacation in the mountains with no internet.