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Thread: Accurate Divergence Calculator

  1. #1
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    Default Accurate Divergence Calculator

    Hi, Y-all.
    I've just built 2 laser modules using Opnext's HL6388MG diode. I did measurements (see pix) and calculated using "Pseudonomen137's JScript mRad Calculator." I got 1.009 mRad. At the aperture fast axis was 5mm and at 65 feet was 25 mm. Does this sound correct? Or might this be Full width half max or something else?
    Thanx in advance.
    -Steve
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    -edit-
    This calculator came up with 1.01 mrad . About the same. I guess they're using the same calculations .. But are they right to the standards?
    Last edited by steve-o; 10-30-2011 at 18:17. Reason: added link

  2. #2
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    Default

    Quote Originally Posted by steve-o View Post
    Hi, Y-all.
    I've just built 2 laser modules using Opnext's HL6388MG diode. I did measurements (see pix) and calculated using "Pseudonomen137's JScript mRad Calculator." I got 1.009 mRad. At the aperture fast axis was 5mm and at 65 feet was 25 mm. Does this sound correct? Or might this be Full width half max or something else?
    Thanx in advance.
    -Steve
    Click image for larger version. 

Name:	DSC00440.JPG 
Views:	25 
Size:	78.4 KB 
ID:	28389Click image for larger version. 

Name:	DSC00439.JPG 
Views:	19 
Size:	59.4 KB 
ID:	28390Click image for larger version. 

Name:	DSC00445.JPG 
Views:	20 
Size:	310.5 KB 
ID:	28391Click image for larger version. 

Name:	DSC00442.JPG 
Views:	24 
Size:	110.4 KB 
ID:	28392

    -edit-
    This calculator came up with 1.01 mrad . About the same. I guess they're using the same calculations .. But are they right to the standards?
    divergence = arctan((Df-Di)/2l)*2

    arctan((25mm-5mm)/39624mm)*2=0.001009 radians = 1.009 mR

    Hints:

    do put the calculator in radians mode before calculating the arctan if you want the result in radians
    If your calculator doesn't have a radians mode there are pi radians in 180 degrees
    don't mix units - if Df and Di are in mm then the length between them MUST be in mm
    if you have the same Motorola Droid phone that I do the scientific calculator sucks *period*
    final hint:
    the tangent of 1 milliradian approximately = .001 on a unit circle - in other words, when you're working with small angles you can skip the arctan calculation, it's already close enough for government work - In fact for artillery, the government rounds pi off to 3.2 - Artillery can be very forgiving of small errors.

  3. #3
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    Thanks for the info, Laserist. (No, I don't have a droid phone, my jitterbug has limited capabilities .. (j/k) .
    I did an experiment with some triangle measurements/ calculations just now, and the results were very close, so I'm concluding that these are full angle measurements and will be acceptable for results.
    Thx again,
    -S

  4. #4
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    Small angle approximation can be used here. (Diameter2-Diameter1)/distance = divergence.

    Diameter 2 is at a distance (mm)
    Diameter 1 is at aperture (mm)
    distance is distance between dot and aperture (m)
    divergence is in full angle (mRad)

    (25-5)/19.81 = 1.009

  5. #5
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    Oh, wow. Simple, easy. Melikes simple! Thanks Xytrell. I'm going to save that one in my 'Lasers' folder :]

    ______________________________________

    So, just to clarify, if anyone (company, etc) lists a laser's divergence as "FWHM" it is actually 1/2 of the total divergence, right?
    Last edited by steve-o; 10-31-2011 at 10:40.

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