MadSci Network: Physics

Re: Why are there no ultraviolet-spectrum laser sights for firearms?

Date: Tue Jun 7 11:57:30 2005
Posted By: Guy Beadie, Staff, Optical sciences, Naval Research Lab
Area of science: Physics
ID: 1117931289.Ph

Hello, Julian.

Interesting question – I hadn’t thought of it before you asked.  In 
principle, there is no reason why one couldn’t make a UV laser sight.  In 
practice, however, there are two big problems: 1) the lasers and 2) the 

The kinds of lasers you’d need (small, bright, yet low-powered and 
electrically driven) are only now coming on the market.  That means that 
they’re too expensive, too short-lived, and likely have too poor a beam 
quality to make a good laser sight.  We can imagine, however, a time in 
the near future in which they’re easily available.  Even then there may 
not be any UV laser sights.

A big problem with a UV laser sight would be viewing a focused image of 
both the laser spot and the target at the same time.  Whether you’re 
looking at something with your naked eye, through a scope, or using a 
camera, the image you see is brought into focus through different optical 
materials – usually lenses.  The problem is that UV light is going to 
focus much differently through these lenses than any other kind of light.  
So, unless you spend an awful lot of money (and size & weight) on 
designing a UV-corrected imaging system, you won’t be able to view the 
laser spot as a small, focused object on your target … which kind of 
defeats the purpose.

I can tell you how large this effect can be from personal experience.  I 
remember the first time I walked into a lab that had optical fibers 
transporting very blue laser light.  Since I could dimly see the blue 
color, it wasn’t even truly UV light.  From the doorway it looked like the 
fibers were about 1/2 an inch in diameter.  When I walked up to the fiber, 
however, I saw that it was the size of any other bare optical fiber: not 
much thicker than a human hair.  What made it appear so thick from 15 feet 
away was the inability of my eye to focus light that blue, when everything 
else from that distance was in focus.

So, there you have it.  A UV laser sight wouldn’t be impossible to make or 
use.  It would, however, be very expensive and complicated.  There would 
have to be a very compelling reason to use UV light in order to justify 
the expense.

Note: I didn’t put in a link to any UV laser company, since such a site 
wouldn’t really be an educational one.  If you really want to know what’s 
available, however, you can always do an internet search on “blue laser” 
or “blue diode laser” … diode lasers are the small, electrically-driven 
lasers that you have in CD/DVD players, and would be the best choice for a 
laser sight.

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