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Divergence

Alaskan

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You can see the spot from a PL520 single mode laser diode on clouds bases up to about 7,000 feet high (when in a relatively dark area without a lot of city lights). DTR sells a set of R, G and B single mode laser diodes which all have low divergence beams when collimated to 4 mm or larger diameter. The longer the focal length of the collimating lens, the larger the beam diameter and the lower the collimated divergence.

Any laser diode can produce low divergence if the beam is expanded enough, even our multimode laser diodes. The worst of them for divergence; the NUBM44 450 nm laser diode, can also have low divergence, but you are going to expand the beam to several inches diameter to get it.

https://sites.google.com/site/dtrlpf/home/diodes/rgb-diode-budle
 



brendon7358

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I'm guessing your PL520 is the *sram unit for $25 on Dtr's sight..
Mine is in a pen size defiant flashlight host and is doing 100mw at .325mA with the G2.
I see your sig shows a 515nm diode, are you not happy with the spec's or is it just under powered?
No, the pl520 was a custom build by someone else when green diodes first came out. I got the 515 hoping the divergence would be comparible to the 520 but it isn't. I am aware of how beam expanders work, I want something that has good divergence with a standard G2 or 3 element lens.
 

Alaskan

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If you look at the raw divergence of single mode laser diode data sheets, if you can find them, you can get a relative idea of which laser diode will produce the lowest divergence, they will show the divergence for each axis of the diodes uncollimated output. Anything with less than 20 degrees in each axis is fairly good, I've seen a few of them down to 15 degrees, even lower to below 10 degrees in the slow axis. One axis will have a larger divergence than the other, unfortunately, but the lower the degrees, the lower the collimated divergence will be for a given lens size. I like using large lenses over 3 inches diameter for my laser pointers, large diameter lenses will tame the worst diverging offenders :) and when used with single mode laser diodes, wow... ultra low divergence.

Edit: I was collecting low divergence laser diode data sheets for awhile, haven't updated my collection with more docs for awhile now, but here's a link to what I have:

https://imageevent.com/qdf_files/technicalgoodies/experimentersfolder/irandlightwavecommunications/laserdiodedatasheets/lowdivergencelaserdiodedatasheets
 
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