DIY Laser Safety: How to Test Pointers and Save Your Eyes

Analog

Lifer
Jan 7, 2002
12,755
3
0

In the last 20 years, green lasers have shrunk from table-size lab equipment to pocket-portable presentation tools (not to mention cat toys). But making laser pointers a household item may have come at a cost. A new study from the National Institute of Standards and Technology reports that some cheap laser pointers can emit more than 10 times as much invisible infrared light as bright green light, making them more likely to blind kids and pets.
“It’s a serious problem,” said NIST physicist Charles Clark, a coauthor of the study. “If green goes into your eye, you’ll probably blink because you can see the green. But with infrared, you won’t blink. The first indication that you have that infrared is coming in is that you’d start to lose your vision.”
Luckily, there’s a science fair-worthy way to test your laser pointer for safety. All you need is a digital camera, a webcam, a CD and a few paper cups.

When green laser pointers first hit the market in the 1990s, they would set you back about $400. These days, they go for as low as $7.75 on Amazon. The average pointer makes its bright beam of light in three steps, each of which was a highlight in laser development when it first came out. “It’s like a little lesson on quantum physics all in itself,” Clark said.
The trick is to convert two photons of long-wavelength, low-energy infrared light into one photon of short-wavelength, high-energy green light in a process called frequency doubling. First, two AAA batteries fuel a diode laser — similar to a standard red laser pointer — which emits infrared light at a wavelength of 808 nanometers. That light gets funneled into a crystal of a material called neodymium-doped yttrium orthovanadate, which is common to lab lasers. The crystal’s electrons respond by getting excited and emitting infrared light at 1064 nanometers, which goes through a second crystal made of potassium titanyl phosphate. That crystal combines two infrared photons into one photon with half the wavelength and double the energy, the familiar 532-nanometer green light.
The standard green laser pointer also includes a shield to keep any of the infrared light from escaping. But in the pointer that Clark and his colleagues examined, the shield was entirely missing. There wasn’t even a holder where a shield should be.
“That was a design choice,” said NIST physicist Edward Hagley, a coauthor of the study. “What we think happened is, if one of the suppliers decides to get rid of the filter and save 50 cents, they can reduce the price a little bit and drive everybody out of business. Then everybody else has to do the same thing.”
Hagley noticed the problem when he bought three $15 laser pointers last December as Christmas presents for his in-laws. Each pointer claimed to emit 10 milliwatts of power, but one of them glowed with a much dimmer green beam. Not only was the dim pointer missing its infrared shield, it also turned out to emit 20 milliwatts of invisible infrared light during normal use. The extra infrared is probably due to a misalignment between the diode laser and the crystals, making the conversion from infrared to green light less efficient.
The total power isn’t that much, about a thousandth of the output of a typical flashlight, Hagley noted. The danger is that laser light is a focused beam of a single wavelength of light, meaning 20 milliwats is enough to burn a hole in your retina before you blink.
“It is a very big safety hazard,” Hagley said. “People who have these laser pointers shouldn’t think they’re safe just because they’re not outputting much green. I know my kids would stick them right in their eyes. And that would be bad.”

So before you let your cat chase a laser pointer beam across the floor, the authors suggest a do-it-yourself test to see how much infrared light your laser puts out. Most digital cameras or camera phones are sensitive only to visible light, but webcams can take images of light well into the infrared portion of the spectrum (or can be easily modified to do so). The authors suggest cutting a few notches in two paper cups, one to stabilize the laser and the other to hold a CD vertically. The CD acts as a diffraction grating, which spreads the laser light out across all its wavelengths.
Place a piece of paper with a hole in it between the laser and the CD, and aim the laser through the hole. The light reflects off the CD and onto the paper, where it can be photographed by either the digital camera or the webcam. Comparing the images reveals how much invisible light your laser produces.
The authors emphasize that you should always take standard safety precautions when doing experiments with lasers: Don’t look into a direct, reflected or diffracted laser source; keep your eyes well above the laser level; wear safety glasses. The precautions are spelled out in detail in the NIST paper.
It’s a simple setup, but it’s impressive even to other physicists. “Their experiment design is very clever and illustrates the problem brilliantly,” commented laser physicist Thomas Baer of Stanford, who was not involved in the study.
This isn’t the only possible test, Clark added. “We wanted to crowdsource a solution to the problem,” he said. “There are other methods people may think up. Having a method out there might stimulate community activity, quantify it further, and perhaps put pressure on the manufacturers to use safer designs.”

Image: 1) Flickr/sara sotin 2) NIST 3) NIST. The top image shows the visible diffraction pattern; the bottom shows extra light in the infrared.

 

lxskllr

No Lifer
Nov 30, 2004
57,420
7,601
126
I think Ruby posted something similar awhile ago. She linked to that article in any case.
 

Wyndru

Diamond Member
Apr 9, 2009
7,318
4
76
Does this mean that if the laser lets out a low amount of infrared, it's ok for pets? I always thought they were all bad for animals, since there is no real guarantee that they will automatically blink when the light hits their eye. I've always been hesitant to play with a laser pointer with my cat.
 

sandorski

No Lifer
Oct 10, 1999
70,101
5,640
126
Just send it FedEx overnight to the folks at the Large Hardon Collider. They'll figure out the precise output.
 

lxskllr

No Lifer
Nov 30, 2004
57,420
7,601
126
Does this mean that if the laser lets out a low amount of infrared, it's ok for pets? I always thought they were all bad for animals, since there is no real guarantee that they will automatically blink when the light hits their eye. I've always been hesitant to play with a laser pointer with my cat.

Don't shine it in their eyes, and keep it moving. That's what they want anyway. A light that just sits there is boring :^D
 

Wyndru

Diamond Member
Apr 9, 2009
7,318
4
76
Don't shine it in their eyes, and keep it moving. That's what they want anyway. A light that just sits there is boring :^D

I'm just figuring I'm going to accidentally expose his eyes to it eventually while I'm bouncing it around. So it doesn't matter if it's for split second while I'm moving it around? I thought any exposure caused damage, even slight.
 

lxskllr

No Lifer
Nov 30, 2004
57,420
7,601
126
I really don't know tbh, but I'm thinking the chance of injury is very slight. The cat's looking at the dot on the floor/wall, so they won't usually be getting direct contact by looking at the laser bore.
 

sandorski

No Lifer
Oct 10, 1999
70,101
5,640
126
I really don't know tbh, but I'm thinking the chance of injury is very slight. The cat's looking at the dot on the floor/wall, so they won't usually be getting direct contact by looking at the laser bore.

All you need to entertain a cat is a flashlight or a shadow(hand in front of light).
 

SoulAssassin

Diamond Member
Feb 1, 2001
6,135
2
0
When we test fiber cables for light I usually pull out the camera phone and shine the light into the lens and look at the screen. Bit different than a green laser I suppose.
 

destrekor

Lifer
Nov 18, 2005
28,799
359
126
Wait... :hmm:

Is the infra-red not shining like the laser?

So, the green visible is from an actual laser - a controlled beam with no light moving anywhere but the path of the laser.

That's why, without a diffraction medium, you don't see the beam, you see where the beam hits.

Can regular atmosphere diffract enough of the light off the path and into our eyes?

Thus, wouldn't the IR light follow the exact same path?

So, wouldn't you have to shine it directly into the eyes for potential damage?
 

Rubycon

Madame President
Aug 10, 2005
17,768
485
126
Couple of things...

First any laser >5mW is NOT a pointer and should NEVER be used as such. Granted it's hard to find even so called 5mW pointers these days that are actually <5mW now because of cheap manufacturing, average efficiency of DPSS conversion AND the pump diode size used...

Even with this it's quite irresponsible to use a Class IIIb laser as a pet toy! Get a dollar store red pointer that WILL be safe if you want to tease cats. They don't care and will see it just fine.

That said, the whole IR thing with POINTERS is just a little overblown - well perhaps a lot. Even without the IR filter in place the amount escaping is not really much of a hazard IF you follow basic (common sense people!) laser safety. The IR will not be collimated nearly as well as the visible emission at 532nm. The IR does not "travel with" the green in a way that it's "highly dangerous" [sic] all the way to beam's end as some would believe. Decent DPSS lasers whether lab modules or cheap pointers, however, SHOULD have an IR filter in place. 808 and 1064 have no business coming out the aperture in a product certified for 532 emission. It also skews proper power readings taken on entry level equipment that's not using a selective metric.

Finally soon there will be direct diodes producing these (desired?) colors directly completely eliminating the rogue IR radiation issue altogether. Of course it brings about another issue - raw power! These are class IV devices (well over 1/2 watt CW!) and that's in another league all on its own.
 

halik

Lifer
Oct 10, 2000
25,696
1
0
Err isn't the IR beam as focused as the laser? Ie if you're not looking into the laser pointer, it's really not an issue?
 

DrPizza

Administrator Elite Member Goat Whisperer
Mar 5, 2001
49,606
166
111
www.slatebrookfarm.com
Bump for this:

checked ebay for a green laser. I'd prefer to get a decent 5mW laser, and a "safe" one at that for a couple of particular uses in my classroom that the red lasers simply don't do a good enough job on. Actually, a 30mW or 50mW that has a safety lock would do even better.

I'm clueless where to get a decent laser though. i.e. I recognize that probably 90&#37; of the ones sold on Ebay as 5mW probably aren't. Anyone?
 

Analog

Lifer
Jan 7, 2002
12,755
3
0
Bump for this:

checked ebay for a green laser. I'd prefer to get a decent 5mW laser, and a &quot;safe&quot; one at that for a couple of particular uses in my classroom that the red lasers simply don't do a good enough job on. Actually, a 30mW or 50mW that has a safety lock would do even better.

I'm clueless where to get a decent laser though. i.e. I recognize that probably 90&#37; of the ones sold on Ebay as 5mW probably aren't. Anyone?

for $24.95: 50mW green: http://ledshoppe.com/Product/ledp/LP1076.htm 50mW violet: http://ledshoppe.com/Product/ledp/lp9008.htm lower power for less money too: http://ledshoppe.com/laserpointer.htm
 

0roo0roo

No Lifer
Sep 21, 2002
64,862
84
91
I'm just figuring I'm going to accidentally expose his eyes to it eventually while I'm bouncing it around. So it doesn't matter if it's for split second while I'm moving it around? I thought any exposure caused damage, even slight.

almost no chance, anyways, you probably have a cheap red laser right?

in any case the cat or dog is looking at the top, not the pointer.

pets are pretty hazard resistant. they simply don't live long enough to accumulate the damage that messes with humans.
 

DrPizza

Administrator Elite Member Goat Whisperer
Mar 5, 2001
49,606
166
111
www.slatebrookfarm.com
@Analog - I wonder if they ship 50mW lasers to the US. I'm not sure what the exact rules are, but saw another company that won't ship >5mW to the US (and >1mW to a few other countries.)