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Micromirror Reflectivity

Daniel --
Prodigy 10 points
Other Parts Discussed in Thread: DLP4500NIR

Hello,


Is there any data available for the reflectivity (in terms of wavelength) for the micromirrors used in the DLP products? Are they the same for every DMD, or are there any special coatings for different wavelength regions?

I am looking for data, especialy for 760-780nm and 1064nm wavelength.

Another thing I would like to ask is, about the damage threshold for the above mentioned wavelengths? I find values for 400-700nm of 25W/cm^2. For the NIR DLP it is between 700-2000nm only 2-4W/cm^2. Since I will need power densities that are around 20W/cm^2, it would be great if there are any more specific details about it. I guess the main damage threshhold is due to the mirror reflectivity?

Or is it possible to get higher power densities for 780nm with the DLP range 400-700nm than the mentioned 10mW/cm^2? (I guess this is just a warranity thing)

Thank you!

  • 0
    TI__Guru 54225 points

    Hello Daniel,

    Welcome to the DLP section of the TI-E2E Community forums.

    Individual µ-mirrors for all DMD devices closely follow the reflectivity curve of bulk aluminum.  Please see the Wikipedia image at:   Aluminum-Gold-Silver Reflectivity  <-- click

    However that is only part of the story.  The total refectivity is also dependent on window transmission and wavelength pixel size and incident angle, which determines the diffraction efficiency.  Please see the technical documentation on window transmissivity at:  Wavelength Transmittance Considerations for DLP DMD Windows (Rev. C)  <-- click

    System optics are also an important part of the effective reflectivity that you can achieve.

    The power handling is determined by a number of factors, but the most important is the size of the thermal interface at the back of the package and to a lesser degree the pixel size.  The devices you list at 25 W/cm2 have a fairly large thermal interface (and also have larger pixels - 13.68 or 10.8 vs 7.56 µm).  The specification for the the DLP4500NIR is based on testing TI has perfrormed.

    You are correct that the specifications in the datasheet are the terms of the warranty for a device.  Although this does not prevent you from working outside these bounds, it does void the warranty.

    This discussion assumes that you are using a homogeneous and continuous light source.  If you plan to use pulsed laser then individual pulse energy becomes important separately from the average array temperature.

    Fizix