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DLP7000: Spectral Reflectivity

Danilo A.
Mastermind 28740 points
Part Number: DLP7000
Other Parts Discussed in Thread: DLP650LNIR

Hi Team,

Our customer is requesting for the following informations regarding our DMD devices.

1. Spectral reflectivity of DLP7000 and DLP700UV at 230nm to 850nm

2. Spectral curve of reflectance of DLP650LNIR at 700nm to 2500nm

Regards,

Danilo

  • 0
    TI__Guru 54705 points

    Hello Danilo,

    Spectral reflectivity is a bit more complex to measure on a Digital Micromirror Device (DMD) that a bulk surface.

    We do publish window transmission data that can be found in this document:

    Wavelength Transmittance Considerations for DLP DMD Windows (Rev. E)

    Then you can use the reflectivity of bulk aluminum as a very good approximation of the reflectivity of the micromirrors themselves.

    However, for the array reflectivity there is an "effective fill factor" that accounts for the mirror gap as seen from the "on state" illumination direction.

    Then the f # of the illumination and of the projection optics and their angles to the DMD array affect the relative reflectivity.

    And last, the diffraction efficiency under these same conditions.This is why we do not publish numbers for the "reflectivity" because it can be misleading.

    In our experience it has been much more "illuminating" (please pardon the pun) to set up a mock-up system on an optical bench and make the measurements.  I regret that we do not have a simpler answer for you.

    What are your requirements?

    Fizix

  • 0 in reply to Fizix
    TI__Genius 9500 points

    Hello Fizix,

    Thanks for looking into this. We've shared this thread to the customer and apparently he wants us to post his responses on his behalf. Can you help us address his follow-up questions below?

    "With regard to the transmission data provided it seems that the window material used for DLP DMD is limiting the reflection from the micro mirrors and not the mirror surface. To my knowledge Aluminum has a high reflectivity all over range 200nm to 900nm (with angle dependency of course). Please correct me if I am wrong.

    We think about using the TI DLP DMD for a set-up using light of range 220nm to 900nm, collimated onto the micro mirror array with angle of incident of 20degree. the micro mirrors are thought to be set to plane position in normal operation mode and tilted when light selection is done.

    1) Can you confirm that window transmittance is the only limiting factor why the DPL DMD is not suitable for wavelength below 300nm?

    2) if so, can you provide a different window material like UV Grad Fused Silica or Anhydrous Quarz or alike (that is more tranparent in UV)?

    3) Can you provide me with the effective fill factor (= reflective area / non-reflection area) for 0°AOI and 30°AOI?"

    Thank you very much for your help.

    Kind Regards,

    Jejomar




  • 0 in reply to Jejomar Ildefonso
    TI__Guru 54705 points

    Hello Jejomar,


    A quick note on reflectivity of the aluminum mirrors.  There is some angular dependence, but it is not significant.3

    You are correct that the primary driver of lower throughput as you go into the UV range is the material of the windows.  Moreover, there are other considerations once you get below 363 nm.  These can be found in this document:

    System Design Considerations Using TI DLP® Technology in UVA (363 – 420 nm) (Rev. A)

    We do not offer DMD's with other window material.

    Moreover, the windows have an AR coating designed for the wavelength range they are intended to be used.  It is very difficult to develop an AR coating that works well across a very broad range of wavelengths (i.e. 200 - 900 nm).

    Regarding fill factors, some of the data sheets have footnotes for the efficiency conditions that sometimes include effective fill factor.  They are typically for 2 x tilt angle (24 degrees for most of our devices).  That would be close enough for a first order approximation.  

    I hope this helps.

    Fizix