Be careful to Dragonlaser goggles

[Arayan]

I did a preliminary test on two safety goggles for green lasers (532 nm), and I found something that I did not expect:
I blocked a green beam (<5 mW Laserglow Anser) with goggles from Dragonlaser and from Elitelasers. Those from DL (OD> 4 for 190-533nm) let through a clearly visible green dot (at various distances), while those from EL (OD> 4 for 200-540nm) totally block the beam (at various distances).
So be careful to use those from DL for high power lasers!!

 

[Asherz]

I also find this when point my greenie through them, but I think this output is IR... Since I'm expecting your green isn't IR filtered, neither is mine and this will cause a small output of light, mixed with a small amount of green light escaping may cause a bright dot.

If I do this with my PHR (405mm) I get no output what so ever through my goggles.

 

[Arayan]

...but I think this output is IR... Since I'm expecting your green isn't IR filtered...

I think it is not IR because the laser has an IR filter (guaranteed by Laseglow) and the dot is visible to the naked eye and green colored.

 

[Asherz]

I think it is not IR because the laser has an IR filter (guaranteed by Laseglow) and the dot is visible to the naked eye and green colored.

Touche, the only other thing I can think of is that DPSS lasers don't always give out exactly 532nm, and the wavelength varys 1-2nm due to different variables?

As an example, a 1 to 5 mW green laser like that in a green laser pointer with a discrete cavity will have an effective cavity length of around 10 millimeters. For the 10 mm cavity, the free spectra range (FSR) - same as longitudinal mode spacing - is about 15 GHz. This is also the maximum shift in frequency of the fundamental that can occur due to temperature changing cavity length before the mode must hop to remain stable. 15 GHz at 1,064 nm is about 1 part in 20,000 or 0.05 nm. But once doubled to 532 nm, the shift becomes only 0.025 nm.

/samsFAQ

That bit of info shows that green DPSS lasers are not going to shift enough to leave the goggles range, I don't have any more theories left :S

 

[Deleted member 8382]

Wait, good goggles must let some green in but keep that input under 5mW. How would you see the dot trough them if they didn't?

 

[Asherz]

Wait, good goggles must let some green in but keep that input under 5mW. How would you see the dot trough them if they didn't?

This is true, but then again when I shine my PHR through my DL goggles, I get no output at all, but when I shine it against the wall and look through my goggles I can still see it, I assume what you see is the florescence due to the violet, but not the actual violet laser output.

 

[Arayan]

Wait, good goggles must let some green in but keep that input under 5mW. How would you see the dot trough them if they didn't?

Yes, I can't see the point if I wearing the goggles but I think that it should be able to block a beam with power ranging between 3 and 5 mW

 

[mfo]

I did a preliminary test on two safety goggles for green lasers (532 nm), and I found something that I did not expect:
I blocked a green beam (<5 mW Laserglow Anser) with goggles from Dragonlaser and from Elitelasers. Those from DL (OD> 4 for 190-533nm) let through a clearly visible green dot (at various distances), while those from EL (OD> 4 for 200-540nm) totally block the beam (at various distances).
So be careful to use those from DL for high power lasers!!

Please provide us with a link showing exactly which goggles you tested. I'm guessing these?

Laser Glasses - UV to Green Lasers Protection 190-548nm :: Laser Safety :: Dragon Lasers

You'll notice that each set of goggles comes with a graph. All goggles will block out different wavelengths of light, some better than others. For example...

You'll see that the slope starts to decline around 532nm in that graph. While it does provide some protection for that area, you are better off buying glasses specifically designed for 532nm where the graph will remain high for that wavelength. Also, you can't hold the laser on the same spot on the glasses. The laser will melt the plastic and bleach the coating, making them useless.

One more thing, don't go by looks alone, use a LPM to confirm your suspicions without a doubt.

 

[HIMNL9]

In most cases, those that are sold as "laser goggles" are NOT laser goggles, but just safety goggles with some degree of protection from UV and/or IR, like the ones that you buy at hardware stores for grinder use ..... the difference is that some of them (very few ones) have a dye in the lenses that effectively block the lasers of some colors (like the ones that i had tested from Focalprice, that are made as UV protections, and have a dye that effectively blocks also the 532nm), where others, instead, are just orange plastic, good for some light UV filtering, but not for any decent laser protection.

I had also one of those light orange safety goggles, same as those that some company sell as laser goggles (i mean, the ones that have the lenses and the frame made in a single mold of orange plastic, not the ones with the black frame and red lenses), and when i've tried them with a 50mW laser, at least 1/4 of the light was passing through, like in the pics that Arayan have posted about dragonlaser ones ..... these are NOT laser goggles, this density is also not just OD1, is only 2 stops !!


Edit: BTW, OD1 means that 1/10 of the light pass, 2 stops means that 1/4 of the light pass ..... forgot to say this, sorry.

 

[mfo]

Edit: BTW, OD1 means that 1/10 of the light pass, 2 stops means that 1/4 of the light pass ..... forgot to say this, sorry.

I thought each OD rating dropped the power by one tenth?

OD1 = One tenth power.
OD2 = One hundredth power.
OD3 = One thousandth power.

 

[Arayan]

Yes, the link is right and according to this graph the goggles should have an OD of around 4 for the wavelength of the laser used (approx. 532 nm) with an average power <3 mW (residual IR less than 1% of total output )

 

[mfo]

Yes, the link is right and according to this graph the goggles should have an OD of around 4 for the wavelength of the laser used (approx. 532 nm) with an average power <3 mW (residual IR less than 1% of total output )

Well, prove they are not up to spec and get a refund then.

 

[HIMNL9]

I thought each OD rating dropped the power by one tenth?

OD1 = One tenth power.
OD2 = One hundredth power.
OD3 = One thousandth power.

Yes, sorry i mixed OD and stops

OD1 = pass 1/10 (or 10%)
OD2 = pass 1/100 (or 1%)
OD3 = pass 1/1000 (or 0.1%)
and so on ..... where instead photographic "stops" just divide by 2 each previous value ..... i mean

1 stop = pass 1/2
2 stops = pass 1/4
3 stops = pass 1/8
and so on .....

 

[Arayan]

Thanks to HIMNL9 and mfo for pointing out the right way to read the Optical Density

I had also one of those light orange safety goggles, same as those that some company sell as laser goggles (i mean, the ones that have the lenses and the frame made in a single mold of orange plastic, not the ones with the black frame and red lenses), and when i've tried them with a 50mW laser, at least 1/4 of the light was passing through, like in the pics that Arayan have posted about dragonlaser ones ..... these are NOT laser goggles, this density is also not just OD1, is only 2 stops !!

in fact I did this test because it seems strange that the lenses were orange when the complementary color of green is red

 

[denton808]

it is possible to not have any dots. i have a 300-360mw+ IR filtered green laser and a orangish safety glasses. when i shine my laser at it there is no dot at all. the light hits the glasses and is immediately dispersed as yellow light. when i wear the glasses and shine on the wall, it is just a yellow dot.

if i had to guess, that is why this safety goggle costs 60 dollars instead of cheapy 10-25 dollar ones. the dot is clearly visible, but it's certain that no gren laser passes through, or at the very least not focused, and mostly just yellow dispersed light.

let me know if anyone has any other thoughts.

 

[HIMNL9]

@ denton: It's not matter of colors, it's matter of how much light pass through them, that grant you some protection, or no protection.

I mean, if you have a lens that left pass 20% of the light, no matter if you see it yellow instead green, it's always too much ..... in the same way, if you have a neutral grey OD3 lens, that left pass 1/1000 of the light, no matter if you see the green, the protection is still decent.

As in my tests, as you see, the beam don't pass through the lens (in the measure cycle), and the dot that you see is orange, but this is probably due to some sorta of low level fluorescence of the paper from the green beam ..... cause if it was green light passed through the lens, it had to be visible also directly, passing the beam through the lens to the paper, where instead is only visible shooting the beam to the paper and looking through the lens ..... and also it had to be measurable from the beam passed through the lens, where instead it's measured only the IR part (that the red goggles don't block)

So, basically, the better way for judge a laser goggle, if you don't have a certification document (and also if you have it, if for that ..... i'm always cautious), is to make some measures with a good LPM ..... and, in case you don't have an LPM, can always do a quick test ..... point the beam through the lens (not focused to burn, for not ruin them) to a piece of white paper, repairing the paper from reflected light ..... if you cannot see ANY spot on the white surface, nor green nor yellow, it can be ok ..... where instead, if for any reason doing this, you can see any spot on the paper, there's something bad in the lenses.