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DLP7000: diffraction

yoshitaka
Prodigy 60 points
Part Number: DLP7000

Hello. 

I am using a DLP7000. It has a usable wavelength of 400-700nm and a micromirror pitch of 13.68㎛.
The light source is a multimode laser diode with a wavelength of 450nm.

Currently, I have tried to set up the projection optics with a single biconvex spherical lens, but it does not handle diffracted light well.

When using a DMD with a coherent light source, diffraction will occur, so how should the optics be designed to collect only the zero-order or up to ±1st- order light?

Thank you in advance.

  • 0
    TI__Guru 54605 points

    Hello Yoshitaka-san,

    Could you give more detail about "it does not handle diffracted light well."  If possible can you show images of the resulting focused spot.

    I would like to clear up some misconceptions.  The 0th order is not always the brightest order, but rather is the order with no dispersion.  If you turn the DMD off so that the mirrors are nominally flat, then the brightest order is the 0th order.  When you turn the mirrors on (or off) the energy will move to other orders.  

    Ideally you should illuminate from about 24 degrees from the array normal (window normal) and at -45 degrees from the top of the DMD.  From the upper left corner in the diagram on page 20 of the DLP7000 data sheet - https://www.ti.com/lit/ds/symlink/dlp7000.pdf. 

    When illuminated this way the energy should move to about the 9,9 order.  However since the tilt angle is 11 - 13 degrees, it may be divided up between the 8,8; 8,9; 9,8 and 9,9 order.  Please look at the following white paper that I wrote:  https://www.ti.com/lit/wp/dlpa037/dlpa037.pdf. 

    Fizix