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DLP7000UV: UV intensity after reflection from DMD drastically decreased.

Anonymous
Anonymous
Guru 17045 points
Part Number: DLP7000UV

Hi All,

We have a DLP7000UV DMD. We use a UV source with spectrum 320-500nm. Previously after reflection from DMD we used to get 25mW/cm^2 intensity when measured with 365nm sensor radiometer, but now with the same setting we are getting only 7mW/cm^2. We checked our UV source and it is working normal. Has the reflectivity of the DMD decreased? We noticed that we were violating the recommended UV range of 365-420nm for the DMD. But what exactly happened to our DMD? And is there any way we can fix it? Also, previously I noticed that the image loaded on the DMD used to look very bright white, but now it looks a bit greyish to me (it is not as bright as before but I am not 100% sure about it).  I have attached our UV spectrum image for your reference. I am also attaching a picture of an image loaded on to the DMD. The white rectangular part on the DMD is our image; does the image look bright enough for you?

Thank you,

Nishedh

  • 0
    TI__Expert 4530 points
    Hi Nishedh,

    Welcome to DLP section of TI E2E community. You forgot to attach the image.

    -ykc
  • Anonymous
    0 Anonymous in reply to ykc
    Guru 17045 points

    Hi ykc, sorry. Here is the image. I have also attached a picture of our DMD with image loaded on it. The white rectangle part is our image. Does the image look bright enough to you?

  • 0 in reply to Anonymous
    TI__Expert 4530 points
    Hi Nishedh,

    Please check Section 7.4 Recommended Operating Conditions in DLP7000UV datasheet. Please check footnotes also.
    There are restrictions on max illumination. Operating the device beyond these limits can cause permanent damage to the device.

    -ykc
  • 0 in reply to ykc
    TI__Intellectual 1875 points

    Nishedh

    The Optical source you are using is rated at 200 W and > 30 W/cm^2 at its output.
    The DLP7000UV is rated for max 2.5 W/cm^2 363-400 nm which is ~3.7 W total measured at the DMD window.
    Have you designed your illumination optics between the OmniCure S2000 output to reduce the optical power to operate within the DLP7000UV data sheet limits?
    Also, you need to ensure the DMD is operated with the micromirror array at 20-30 Deg. C when used with light sources below 420 nm.

    Please see our application note Considerations Using TI DLP® Technology in UVA (363 – 420 nm) www.ti.com/.../dlpa060

  • Anonymous
    0 Anonymous in reply to Carey Ritchey
    Guru 17045 points
    Hi Carey,

    We do not have any filter or anything between our UV source (spectrum 320-500nm) and the DMD. However, we have never used more than 25mW/cm^2 UV intensity on our DMD. So, what caused the DMD to fail? We want to prevent this from happening in future so we are looking for the cause.

    Thank you,
    Nishedh
  • Anonymous
    0 Anonymous in reply to ykc
    Guru 17045 points
    Hi ykc,

    We know our UV spectrum (320-500nm) was not within the specifications (363-420nm). Our DMD is directly exposed to the UV source without any filter in between. We generally use 25 mW/cm^2 illumination. The recommended UV intensity for <363nm is 2mW/cm^2. So, maybe the UVs at shorter wavelength caused this problem. But, what does "permanent damage" mean? Like what kind of damages?

    Thank you,
    Nishedh
  • 0 in reply to Anonymous
    TI__Intellectual 1875 points

    Nishedh

    How are you reducing the optical source power (OmniCure S2000 output) to  have a typical  25mW/cm^2 output from the DLP7000UV.

    What is the effective power density of the sourced measured at the DMD window ?

    Reduction in DMD efficiency is typically caused by operating the DMD with UV power density outside of the data sheet limits, this effect will be greatly accelerated if the the DMD mirror array temperature is not operated in side the data sheet limits of 20-30 Deg. C.

    See section 9.1.1 and figure 18 of the DLP7000UV data sheet http://www.ti.com/lit/ds/symlink/dlp7000uv.pdf

    Carey

  • Anonymous
    0 Anonymous in reply to Carey Ritchey
    Guru 17045 points

    Carey,

    Attached is a schematic representation of our system. The optical power source can be varied from 0-100%; if we keep it at 50% we get 25mW/cm^2 UV intensity at our stage. The intensity on DMD mirror may also be around the same value ( I think). Also, we are planning to use a 365 nm filter between the source and our new DMD mirror. I have attached its spectrum output here. Do you think we can use our DMD at 25mW/cm^2 intensity with this filter? Note: though the spectrum has peak at 365 nm, it also has some shorter wavelength UVs, so will that affect our DMD again? Please suggest.

    Thank you,

    Nishedh

  • 0 in reply to Anonymous
    TI__Intellectual 1875 points
    Nishedh

    When you are using power per unit area you need to account for the magnification / demagnification of the projection path along with its losses
    You need to measure and know the optical power at the DMD window.

    Measuring the optical power density at the final output does not tell you the power at the DMD input, or the optical losses in the projection path.

    Along with the optical power density at the DMD window have you measured the optical losses through the projection path?
    UV light can quickly damage optical coatings on the elements greatly increasing their losses as well.

    Carey
  • Anonymous
    0 Anonymous in reply to Carey Ritchey
    Guru 17045 points

    Carey,

    We have not measured intensity at the DMD mirror. We only measure it at the stage. Also, what do you think about the above attached spectrum of 365nm filter? What maximum intensity at the DMD is safe to use with that spectrum? Please suggest. We are getting our new DMD soon and we want to use that filter if it is safe.

    One more thing: can we use non contact infrared thermometer to measure DMD temperature?

    -Nishedh

  • 0 in reply to Anonymous
    TI__Guru 50025 points
    Hello Nishedh,

    The filter will help, but you really need to get a measure of how much energy is incident on the DMD. This will give a better understanding of the power on the micromirrors.

    Regarding temperature, we have found that using an infrared thermometer is challenging since what is usually seen is the temperature of the window surface.

    It would be better to have an idea of the incident power, the outbound power in the off state (so you can determine how much was absorbed), and a thermo-couple on the back of the DMD at the location described in the DLP7000UV data sheet (§ 8.6.2 on pg 34). Then you can use the information with the Array Temperature Calculation (§ 8.6.3 on pg 35).

    Fizix