• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 31 subscribers
  • Views 776 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DLP 4100 kit IR reflection efficiency

Cameron Simmons
Prodigy 20 points

Can anyone tell me the correct way to mount the DLP 4100 DMD with respect to an incoming light source?  I thought I had mounted at the correct angle but am experiencing poor reflection efficiency, (around 50% when I expect about 95%,) and with the mirrors all in the "on" state using the explorer software I get about 3 beam reflections with small angular deviation from each other and they are all very dim.  Putting all mirrors in the "off" state produces one reflection with higher efficiency but I would like to use the "on" state. 

For specifics regarding my setup, I am shining the light in at 24 degrees from normal incidence and at 45 degrees from the horizontal axis of the mirrors.  I am hitting the DMD with 400 mW of power from a 1064 laser with about a 5mm spot and am measuring 247 mW from the "off" state reflection, 165 mW total from the "on" state reflection in 3 beams with a slight angular spread, and 277 mW from the "floating" state reflection.  I appreciate any help!

Thanks!

Cameron

  • 0
    TI__Guru 54705 points

    Hello Cameron,

    Welcome to the DLP section of the TI-E2E community. 

    First, are you using an IR optimized DMD or a visible DMD? 

    I am guessing that several things are happening here:

    1. Although the mirrors are made of aluminum and the reflectivity is up near 95%, there are also diffractive losses, window transmission losses and "fill factor" losses.  At the very best you might get somewhere around 80%. [Unless you mean 95% relative to the "floating" state reflection.]
    2. Since you indicate that there are 3 spots with slight angular deviation from each other this sounds like you are getting mutiple reflections in the window.  This leads me to believe that you might be using a visible DMD whose window is not optimized for IR.
    3. Since you are using collimated coherent light with the DMD you should be seeing diffraction orders.  The order nearest the "on" state may or may not be in a "blaze" condition for 1064 nm. 

    Which DMD are you using (i.e 0.55" XGA vs 0.7" XGA vs 0.95" 1080p)?

     

    Fizix

  • 0 in reply to Fizix
    Prodigy 20 points

    Thank you Fizix,

    The box says 0.7 XGA IR DMD.   I had that idea too that maybe I received the incorrect coating but I think I have the right coating.  The efficiency I reported is based on the numbers in my earlier post.  I  input 400 mW and got those powers after reflection off the DMD.

    I hear what you say about the diffractive losses and window transmission losses but I am not getting close to 80% and should I expect such a wide range in output intensities between the off, on and floating states? 

    I also am thinking you are right about the diffraction causing the spots in the on state.  I am certain the reflections are not off the window because they go away when not in the in different states.  Did my orientation for the DMD with respect to the incoming light sound like it was the appropriate angle?  I may have to play around and see what happens.

    Thank you for your help!  It is very appreciated to have someone to talk this through.

    Cameron

  • 0 in reply to Cameron Simmons
    TI__Guru 54705 points

    Hello Cameron,

    Since you verify that you are using an IR DMD then I agree with you that window reflection is not likely to be the culprit.

    As far as the wide range of variation between the off state and on state, the answer is that it is quite possible.  Please check the paper I wrote concerning using DMDs with laser illumination:

    focus.ti.com/pdfs/dlpdmd/Using_Lasers_with_DLP(r)_Technology.pdf

    Fizix

  • 0 in reply to Cameron Simmons
    Intellectual 500 points

    Dear Cameron, I just wanted to add a tip with regards to adjusting the coherent illumination on the DMD .

    When you are illuminating the DMD with a laser source without imaging involved you'd be able to see the diffraction effect and if you look closely you can see those dots you mentioned.   Now if your angle is set correctly the dots astigmatism should be minimal, meaning as close as possible to full round circle rather than oval. you can move the system and watch the dot's until you set it to an optimized angle by watching the ratio of the two axes. 

    Since you are using a NIR laser, you could use a camera connected to a computer or monitor for support you in the adjustment process.

    Regards,

    Yuval