Help with safety Glasses OD7 532nm 5mW

[Merrick15]

Hello,
I am new to this laser forum and wanted to ask a couple question to someone with experience working with laser safety shields/goggles.

To start, I will provide information about the laser I am using. I am using a 532nm 5mW green laser that is fitted into a SIRT laser training pistol. I use the SIRT pistol for dry fire practice on cardboard scale targets in my apartment at an average distance of 3 yards. The green laser hits on cardboard targets are read by a computer software called L.A.S.R to give feedback on shot time and accuracy.

I purchased a pair of NOIR ARG OD7 for 532nm safety glasses for two purposes. The first, is I am concerned about repeated exposure at close distances to diffuse reflection from my green laser causing eye damage. I am purposely not blinking to maintain a good sight picture of my SIRT pistol sights. So safety is my main priority.

The second reason I purchased these glasses is the high optical density would prevent me from seeing the laser dot emitted from the SIRT pistol on my targets because the glasses should block the reflected green laser radiation. The advantage to not being able to see the laser impact because of the glasses is that I have to totally rely on my pistol's sight picture, the way one does with a real pistol. Seeing the green dot on a target can allow a person to visually walk their shots onto target, or become target focused which is bad in competitive shooting sports.
[URL=http://s53.photobucket.com/user/bauman32/media/IMG_2294.jpg.html][/URL]



My issue with the glasses are that I can still see a white dot image of the laser off a target through the glasses.
Ex) view looking through at laser hit
[URL=http://s53.photobucket.com/user/bauman32/media/IMG_2296.jpg.html][/URL]

However, when I shine the laser directly through the goggle there is no dot image of the laser projecting through the glasses.
[URL=http://s53.photobucket.com/user/bauman32/media/IMG_2298.jpg.html][/URL]



Can anyone please explain why the direct laser is blocked but the diffuse reflection is visible as a white/orange dot?

 

[diachi]

Looks like there is some mild fluorescence on the surface your laser is hitting - producing an orange glow that's not normally visible due to the brightness of the green dot. Once you put the glasses on the green dot is blocked, but the orange can come right through.

 

[Merrick15]

Although it could be a issue with fluorescence I am doubtful that is the issue. My understanding of fluorescence with green lasers are that it can cause orange reflections of the green laser off of orange objects. All objects that I shine my SIRT pistols green laser on are green when viewed with the naked eye.

My issue is regarding my safety goggles and the ability to see a laser dot even through glasses that are rated OD7+ 180-532nm which includes the wavelength of my laser.

I can always see a dot projection off the object my laser is illuminating when viewed through my safety goggles, as illustrated in the images in my first post.
However, when I shine my laser directly through the OD7+ safety glasses no laser dot is visible beyond the filter lens. In this case the goggles do what they are designed to and filter out all of the green laser wavelength.

I would like to know why the laser dot is visible when viewed through the glasses. Shouldn't the laser dot I am viewing through my googles be filtered out? It is surprising to me that the dot is not visible when the laser is directly shined through the glasses filter lens but is visible when looking through the glasses at an object the laser is illuminating.

I have this issue with both pair of safety glasses I have purchased. One is OD7+ 180-532nm from NOIR laser shields. The other pair are OD5+ 190-532nm from Phillips Safety products.

Can anyone explain this?

 

[diachi]

Can anyone explain this?

Yes, fluorescence - a shorter wavelength photon (green, 532nm) being absorbed by a material which then emits a longer wavelength photon - in this case orange.

The laser dot itself isn't visible, the longer wavelength emission from the material (caused by the laser dot) is visible because your glasses don't block that wavelength - if anything they'll enhance your ability to see orange and red by filtering out other wavelengths in the blue-green part of the spectrum.

Point the beam at a piece of unpainted/uncoated steel, or some other uncoated/unpainted metal - you won't get the orange dot that you do elsewhere because the metal won't fluoresce. You might see a hint of something from the glasses themselves fluorescing, but it shouldn't be to nearly the same extent as with a white painted wall.

Here's an example - but with UV instead of green:

There is *NO* blue laser emission here, that laser is UV (Short wavelength), completely invisible to both the naked eye and the camera. The blue (longer wavelength) you see is from a sheet of paper fluorescing. On a piece of metal the dot is completely invisible because the metal doesn't fluoresce. Same thing happens with your green, you just end up with a different colour, in this case, orange.

 

[Merrick15]

Thanks Diachi,
The second explanation made much more sense to me. As you recommended I tried out a piece of untreated steel from a kitchen spatula and had no visible dot viewed through the glasses.
[URL=http://s53.photobucket.com/user/bauman32/media/Mobile%20Uploads/image_4.jpeg.html][/URL]
[URL=http://s53.photobucket.com/user/bauman32/media/Mobile%20Uploads/image_3.jpeg.html][/URL]

I appreciate you helping me understand what is going on here. The phenomenon of Fluorescence sucks for my intended purposes but at least I am no longer mystified....Still frustrated by it but no longer mystified. Thanks again for the education with this issue.

 

[Laser Chick]

I was going to suggest point the laser at a multitude of different materials as I have seen a phenomena like this using a 405nm laser.
Darn good information diachi :gj: :beer:

 

[diachi]

No problem I'm not sure how you are set up but perhaps you can use a material that doesn't fluoresce for your target? That is if you can use a different material, I'm not sure how the tracking works!

@Laser Chick - Thanks! Yeah, same effect as 405, but 405 being a shorter wavelength allows you to get blue and green fluorescence as well as orange. It's much more noticeable with 405 than with 532 though because it's typically not very bright and it causes bright fluorescence on so many materials.