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DLP4500NIR: NIR optical system alignment

Marco Tramacere
Prodigy 155 points
Part Number: DLP4500NIR

Hello everybody

I'm setting up my own spectrophotometer in NIR region (1300-2500nm)

I just want to know from you the best way to align the optics, filter, grating, DMD, detector. My light source is a traditional tungsten bulb lamp

I have been thinking that it could be done through a laser pointer (whose wavelength should lie in the 1300-2500nm region): putting the laser pointer as source and maximize the response from detector

Let me know if exist a way more professional and suitable (how did you do with DLP NIRscan EVM?)

Thank you very much

  • 0
    TI__Mastermind 30600 points
    Hi Marco,

    Give me a little time to look into this and see what recommendations we're able to provide you.

    Thanks,
    Paul
  • 0 in reply to Paul Goedeke
    TI__Mastermind 30600 points
    Hi Marco,

    Have you taken a look a this application note: www.ti.com/.../dlpa049

    Pages 7 to 9 should be of interest to you.

    -Paul
  • 0 in reply to Paul Goedeke
    Prodigy 155 points

    Hi

    I have taken a look to the pdf document but it doesn't explain how the optical alignment has been. Don't you know how it is done? Someone of you has designed the optical path and has to know it somehow

    Thank you

  • 0 in reply to Marco Tramacere
    TI__Expert 6995 points

    Marco,

    The NIRscan optics was designed taking into account the manufacturing tolerances of slit position, grating angle, DMD position, and optical lens position. To allow for mechanical tolerances, the slit image on the DMD is underfilled in the dispersion axis and overfilled in the orthogonal axis. This allows the proceeding factors to be compensated electronically, greatly reducing manufacturing time. The degree of underfill chosen should be matched to a tolerance analysis, which shows the expected location of the image of the slit. In most cases, the resolution of the DMD far exceeds the required measurement resolution. 

    However, the slit must be actively aligned during manufacturing. The slit position is adjusted to focus the slit on the DMD by running scans and looking at the detector signal to find the peak signal. 

    Mechanical design included features that serve as light traps for reflected light from light-blocking filters, unused reflected grating orders, and DMD off-state light. These mechanical features force these rays to undergo multiple reflections before bouncing back to the detector. In order for these light blocks to be effective, the chassis was coated with a wavelength absorbing coating in the NIR region. 

    Wavelength calibration is performed at the factory through the use of a NIST calibrated light source and determining the location of the peaks and were they land on the DMD. Also, optical distortion is compensated by looking at how these peaks lie across the height of the DMD. During manufacturing, the curvature of the slit on the DMD is analyzed and a set of calibration factors are created to bend the patterns to match the optical curvature of each system.

    Best regards,
    Pedro