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Thread: Opinions regarding divergence based on laser diode output aperture and spread?

  1. #1
    Join Date
    Aug 2014

    Default Laser diode divergence question

    Can someone please help answer this diode divergence question for me?

    I can calculate the divergence of the raw uncollimated output of a laser diode by knowing how wide the slow and fast axis beam outputs are in degrees, but I am thinking the emitter size also plays a part, true? If my thoughts are correct, I could determine the divergence from a specific diode by knowing the emitter aperture size and how many degrees wide the slow and fast axis rays are? Will knowing these figures alone allow the amount of divergence to be calculated for a specific beam diameter after collimation?

    If interested, here is the diode I want to calculate the divergence for if expanded and collimated to a 100mm wide beam: and data sheet

    The emitter size is 1 X 3 um, extremely small! If I remember the man right, I was once told I could divide the emitter aperture by the diameter of the collimated beam output to determine the expansion factor for a diode output and from that the divergence, if also knowing the angle of spreading the diode produces from each axis.

    Is this how it is done? Divide the size of the expanded beam by the diode aperture or emitter size to determine the expansion factor, then divide the diodes raw output in mRad by the amount of expansion to get the expected divergence after collimation? For a fast axis of 30 degrees, I'm calculating that is equal to about 523 mRad, using that fugure, the 3um size of the emitter and expansion when using a 100mm diameter lens, I'm showing an incredibly low amount of divergence for the fast axis, after collimation, am I correct that this calculates to .0156 mRad? What would the real world mRad likely be?

    I've been told the practical mRad would probably be closer to .1 at best due to optical problems, anyone think I could get a lower number? Using the .0156 mRad figure, if comparing the power delivered 1000 meters distance away between a 1.5 mRad laser and a .0156 mRad laser of the same output power, there would be several thousand times the intensity at a 1000 meter distance delivered by the .0156 mRad laser, over five thousand times more power six miles away. Doing the calculations comparing a 1.5 mRad laser output to a .1 mRad, the figure is much less, about 125 times more power. If I can achieve .1 mRad with this laser diode into a 100mm diameter lens I would be very satisfied.

    Last edited by Laser57; 11-10-2015 at 16:40.

  2. #2
    Join Date
    Aug 2014


    OK, I was able to get the answer from a LPF member, gave up, too impatient I am! But on another subject, does anyone know if there are any IR single mode laser diodes with emitter sizes smaller than 1 x 3um ? If so, where might I order one?

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