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Difference in Collimating Lenses?

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Hey again everyone, my last post was talking about problems with creating a 300mw laser with one of those cheap laser diodes from eBay. Since then, I've go that working, and have also made a 200ish mw blu-ray laser from a blu-ray sled laser diode. I have pulsed it at like 80Hz with a 555 timer, (for visual effect, not actual purpose)

Basically the blu-ray laser diode is in a housing with a collimating lens meant for a 808nm laser. I have focused it to infinity, and it is fairly clear.

Would investing in a collminating lens for a violet laser make the dot clearer, and more in focus?
 

DrSid

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There are two main parameters of the lens. Output aperture size and losses.
Aperture size defines diffraction limit, and thus divergence - larger lens = smaller dot (at any distance).

Losses are affected mostly by reflections on the lens elements surfaces, and sometimes also in the lens material. Both are highly dependent on wavelength. This is why we use different lens for UV and IR. Lens which we use for visible and near visible spectrum usually differs only by different coating, to lower losses by reflection. The difference between 808 and 405 could be tens of %. Even some lens for same wavelength differ by 10% or more, the coatings are just that important.

So if you would use 405nm tuned lens of same diameter as those 808nm lens, you will get more power, but same divergence. Same dot size. The power can improve drastically however.

If you would use larger lens, you would get better divergence and better dot. But those are hard to get.

Different lens can also have different quality. Cheap plastic lens will not focus so well, will get scratched easily, and can have bad beam splash. Expensive glass lens are usually a lot better.
 
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