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DLP7000UV: Diffraction light

Taka
Prodigy 30 points
Part Number: DLP7000UV

Hello
I am designing a laser processing machine using DLP7000UV.
We are currently in the process of creating and experimenting with a prototype.

We are verifying that diffracted light is generated in front of the imaging lens and is having a negative impact on the distribution on the workpiece surface.

Please refer to the attached PDF file for the results.
Contents of the PDF
P1: Equipment configuration
P2: Photo: Unevenness in front of the imaging lens
P3: Photo: Mirror on/off in front of the imaging lens

I have a few questions regarding this.

Q1. Is the unevenness in front of the imaging lens due to diffracted light?

If it is diffracted light, why does diffraction occur?

Is it due to the relationship between the DMD mirror structure and the laser wavelength used? The laser used is a multi-mode laser that uses light bundled with several laser diodes, so I thought that the wavefront of the light would be uneven and diffraction would be less likely to occur, but is this not true?

Q2.
If diffracted light occurs in front of the imaging lens (2), will it have a negative effect on the distribution on the workpiece surface (3)? Has such a thing been a problem in the past?
For example, the drop in output. Deterioration of distribution uniformity, etc.

Q3.
Is there a way to eliminate the diffracted light?
Is there a good optical design method to eliminate diffracted light?

Thank you for your advice.

Q20240502.pdf

  • 0
    TI__Guru 54350 points

    Hello Taka,

    Q1. Is the unevenness in front of the imaging lens due to diffracted light?

    This is possible, but this really needs an optical engineer to model the system to be sure.

    If it is diffracted light, why does diffraction occur?

    Diffraction occurs as a fundamental interaction of the periodicity of the laser (temporally and spatially - i.e. frequency and wavelength) and the spatial periodicity of the array of DMD micro mirrors.  

    Is it due to the relationship between the DMD mirror structure and the laser wavelength used? The laser used is a multi-mode laser that uses light bundled with several laser diodes, so I thought that the wave-front of the light would be uneven and diffraction would be less likely to occur, but is this not true?

    The variation in the multimode laser is still not enough to overcome the diffraction effect.  It may make it a little more diffuse.  It may be possible to use a beam expander and then use a larger collection cone on the output optics to help further.

    Q2.
    If diffracted light occurs in front of the imaging lens (2), will it have a negative effect on the distribution on the workpiece surface (3)? Has such a thing been a problem in the past?  

    Please see the answer to Q3.  There are ways to mitigate these effects, but I encourage you to employ a design partner experienced with DMD optics.  Here is a link to possible partners.

    For example, the drop in output. Deterioration of distribution uniformity, etc.

    Q3.
    Is there a way to eliminate the diffracted light?  Please see the previous answer to Q1 - this is a fundamental interaction of laser with the DMD.


    Is there a good optical design method to eliminate diffracted light? 

    If you are using a very small numerical aperture (NA) this will be difficult.  If you can increase your NA then when the imaging optics re-converge the image at the production surface you should get better uniformity.

    Fizix

  • 0 in reply to Fizix
    Prodigy 30 points

    Thank you very much for your reply.

    May I ask you an additional question?


    Q1
    Is there an optimal optical calculation software that can be used to model "this really needs an optical engineer to model the system to be sure"? Currently I am using "ZEMAX Optic Studio". Can this software calculate the diffraction of this DMD? Or do I need software that can calculate diffraction phenomena or handle wave optics?

    Q2
    Excuse me. I was unable to find a link to a design partner with experience with DMD optics. Could you please provide the link again?

    Q3
    thank you. I understand.
    Are there any published examples of optical systems that suppress diffraction? I'd like to use it as a reference for my design.

    I would appreciate it if you could continue to respond.

  • 0 in reply to Taka
    TI__Guru 54350 points

    Hello Taka,

    I hope you had a good weekend.

    Q1

    Is there an optimal optical calculation software that can be used to model "this really needs an optical engineer to model the system to be sure"? Currently I am using "ZEMAX Optic Studio". Can this software calculate the diffraction of this DMD? Or do I need software that can calculate diffraction phenomena or handle wave optics?

    Let me talk to our optical engineers to see what they might recommend.

    Q2
    Excuse me. I was unable to find a link to a design partner with experience with DMD optics. Could you please provide the link again?

    I am sorry, apparently the link did not populate correctly.  Here it is again:

    https://www.ti.com/tool/DLP-OMM-SEARCH  - scroll down to "Order & start development"

    Q3
    thank you. I understand.
    Are there any published examples of optical systems that suppress diffraction? I'd like to use it as a reference for my design.

    Again, let me talk to our optical engineers to see what they might recommend.

    Fizix

  • 0 in reply to Fizix
    Prodigy 30 points

    Hi,Fizix

    Thank you very much for your prompt reply.

    Q1
    I look forward to your reply.

    Q2
    Thank you for the link. I would like to check these lists and decide whether I should consult with you.

    Q3
    I look forward to your reply.

    that's all
    I would appreciate it if you could continue to give me advice.

    Taka

  • 0 in reply to Taka
    TI__Guru 54350 points

    Hello Taka,

    Q1:  We are working on the release of a Matlab runtime model of diffraction that should be out by the end of next week.

    Q3:  They are still looking into this.  Please allow a couple more days.

    Fizix

  • +1 in reply to Fizix
    TI__Guru 54350 points

    Hello again Taka,

    Q1:  The diffraction model has been released and can be found here:

    https://www.ti.com/product/DLPC410#design-tools-simulation 

    Scroll down to this item.

    Q3: I am sending a friend invite to see if we can connect more directly on this.

    Fizix

  • 0 in reply to Fizix
    Prodigy 30 points

    Hello Fizix,

    Thank you very much for the reply
    I'll check out the site you introduced.

    Taka