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ArcticMyst Security by Avery

Host Ideas - Post your wild ideas, dream pointers.

Jan 29, 2014
How about a 8X paralleled NDG7475 520 nm laser pointer using 1" collimators? This filter wheel can be the lens mount for a fairly large multi-diode laser pointer. However, that wheel is a lot larger than need be due to the spacing between lenses, maybe better to have someone machine something, but gave me an idea when seeing it on ebay.

If using this filter wheel 25.4 mm diameter lenses can be had fairly easily, but eight of them cheaply on ebay? Not likely, at least, for the focal length needed which I am calculating to be about 25 mm for the maximum beam spread angle from a NDG7475 520 nm laser diode (to be sure no clipping), the lower spec (good luck finding a real specification on this diode from Nichia) is reported to be about 45-46 degrees average (sources vary).

EdmundOptics.com offers AR coated 25.4 mm Dia 25 mm FL PCX lens for 36 dollars each in quantity of ten:
This begs the question, what focal length lens can be used with a laser diode with 35 degrees of raw divergence and stay within 25 mm diameter? Use this online calculator to determine the beam diameter from a laser diode at a given distance from the lens:

After a few iterations this result (if the beam divergence is 35 degrees), the FL can possibly be as long as 38 mm, but better to calculate for the typical divergence.


Above result: The diameter of (one side) of the beam from a 35 degree divergence laser diode at a distance of 38 mm would be close to 24 mm. Maybe too close to the full width of a 25.4 mm diameter collimation lens as collimation lenses are often only used to about 80% of their diameter, but for a laser pointer, might not be so critical, but a NDG7475 diode typically will have a divergence which is about 11 degrees wider.

Below: The 46 degree beam divergence of a typical NDG7475 laser diode would require a shorter FL collimation lens (if limited to 25 mm diameter):

I've heard this is a faked Nichia spec sheet but according to this, the divergence of the wide side can be as low as 35 degrees, but also as high as 50 deg! Perhaps better to choose a different FL lens to fill the diameter of the lens more for slightly lower divergence, maybe 20-21 mm FL?

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