A Cheap Green Laser

Posted 2006.09.10 1.00 in Lasers

When I was new to the exciting world of high-power green lasers, like many folks I didn’t really know much about what I was getting in to. I had learned that there were pocket-sized ‘laser pointers’ that could pop balloons and light matches, and I wanted in on that kind of fun.

I had found the Wicked Lasers web site and saw what they had but it seemed kind of pricey. So like many of us, I went to ebay to see what was there, cheaper.

I should have known better because a) cheaper means both ‘less expensive’ and ‘poor quality’, and b) if something seems too good to be true then it probably is.

Nonetheless, I soon found an auction listing for an ’80mW Green Laser Pointer’. The price was almost $100 less than Wicked Lasers wanted for their 75mW laser. And the vendor was in Canada, which meant faster shipping and no duties / brokerage, and no hassles at the border. So I plunked out the money, and in a few days, it arrived.
green ebay laser


The Good, Bad, and Uncertain

Sure enough, the first match I put it to ignited almost instantly. I was wowwed, I was happy. Strangely though, the second match I tried, smoked a bit then did nothing at all.

Soon I realized that it was only super-powerful in the first few seconds. Then its power tapered off considerably. You could even see it, shine the bright green dot on a white wall and it went from blinding, to just bright, really fast.

During all this time, I was still reading and learning and gaining more experience. I quickly learned the complicated way that green lasers work – much more complicated and finicky than a red laser pointer. Over at Green Lasers UK they have a great little tutorial on how green lasers work and how they differ from red lasers. Suffice to say, I soon understood that there are two ways to state laser power: peak, and average. Wicked Lasers might cost more but the stated power is their average. Cheap lasers usually seem inexpensive because they quote you the peak power – a rating which it might only attain once or twice, if ever.

By this time, I had decided that I wanted to get involved with lasers quite a bit, so I decided to invest in a laser power meter. The LaserCheck by Coherent was the most inexpensive, small meter that would work fine for the ranges I was looking for.
Coherent LaserCheck

So I got my meter, checked all my lasers, and lo and behold, it worked for all the red and infrared ones, but not the cheap green one! The reading was crazy, like over 400mW! Was my new LaserCheck not working? No, it works fine. I soon learned that the LaserCheck, which measures optical brightness, is easily confused by multiple-wavelength lasers. My ‘green’ laser was putting out green at 532nm, but also infrared, at 808nm and/or 1064nm. (For information as to why there is IR in a green laser, see the link above.)

Aha! Here is another way for the unscrupulous to get away with selling what seems like a high-powered laser. If you take a cheap green 5mW pointer and remove the IR filters, you will still have 5mW of green light, but now you also have a lot (as much as over 100mW) of IR light as well! So you can sell your cheap green pointer, as a 50mW, 80mW, or even 100mW laser, make lots of money, and claim that you are not lying since it is in fact generating that much IR!


Safety Matters

So what’s wrong with a little IR in the mix? First, it’s not a little it’s a lot. Second, it’s invisible, you can’t see it. Third, if you’re relying on laser goggles rated at 532nm to protect your eyes, you may as well wear no goggles at all because they won’t do anything to block the IR, and worse than nothing, you might take some extra risks in the belief that your eyes are protected since the green dot is dull and doesn’t hurt to look at! Additionally, the IR is not as well-collimated, so it spreads out more, which means you might not even know you’re getting dangerous specular reflections of IR in your eyes, because the green is not reflecting your way.

Wicked Lasers sells great laser goggles at a great price – but they are not rated for IR! If you buy cheap lasers, shell out for expensive goggles. If you buy quality lasers, you can afford the lower-priced goggles. Where would you rather spend your lasers-money? Good expensive lasers, or goggles?

Wicked’s goggles work well for the wavelengths they’re designed for. These pics compare what the goggles look like to your eyes, and what they look like to infrared laser light:
Goggles for different lasers
   
Guess which ones are for IR Lasers
If you were relying on goggles for 532nm (the orange/red lenses) and your laser had lots of IR in it… well you get the point right?

Ok sure, the weak green laser might burn pretty good because it’s got all that IR in it. But it will only burn stuff good up close, because the IR isn’t well-collimated. And you might be slowly and unknowingly losing your eyesight, every time you use the laser!

See, there are no pain receptors at the back of the eye. You can’t see the IR so there is no blink response or aversion response. And the brain is very adept at compensating for partial vision loss, by filling in the blank spots with information from the opposite eye. Most people don’t even know they’re born with a 10 degree blind spot in both eyes (where the optic nerve enters) because the blind spot in the right eye is compensated with data from the left, and vice versa. So little bits and pieces of your vision might be slowly going away, permanently, and by the time you realize it, it is far too late to do anything! This is why having IR mixed in with your green laser is unsafe.


Knowledge Is Power

Ok. So I have established that my cheap green laser has a high initial peak but then quickly tapers off, and I am pretty sure it has no IR filter. A few more tests pretty much confirmed the IR filter situation: I took photos of the dot, using a DV Camera in normal and in ‘nightshot’ mode. In ‘nightshot’ mode it can see near IR light, and the results were pretty conculsive, and obvious.
IR halo around green dot
Here you can see the IR ‘halo’ clearly visible around the green dot. The dot is distorted and stretched because it is being refracted through a cheap plastic prism.

Still learning more, I finaly found out what brand-name the laser is appearantly made by. It’s a NewWish, which are a new manufacturer in China. The manufacturer probably aren’t trying to be malicious; appearantly they’re relatively new and they just produce what is ordered. If the distributor wants to save a dollar or whatever by omitting the IR filter, that’s them, not the maker’s fault.

What is bad of course are all the guys on ebay and elsewhere, hawking these things, and they don’t even know about the potential hazards. Or if they know, they don’t care.


Fixing It

Ok, so I’ve got a laser which is potentially dangerous to me and others around me. I smartened up and ordered a WL Fusion 125mW but in the meantime I’m not just going to throw out the cheap green laser. What to do?

Obviously the answer is to add an IR filter. The caveats: If it is just a cheap green pointer, then adding the IR filter will make it safe, and also reduce it to being just a cheap pointer. No burning power, no balloon popping. Just boring old safety. But, these are the risks you run when you buy on the cheap.

So, where to get an IR filter, and how to know if it’s working? Edmunds Optics sells IR filters that cut-off just over 700nm and also pass over 90% of the green wavelengths, so they’re a good choice. A bit pricey though, at $40-ish for a 12.5mm size. Talk about adding insult to injury, eh? Buy an overpriced unsafe laser, then spend another $40 to make it safe and take all the fun out of it.
IR filter

I’m still looking for cheaper sources…crap there’s that word again, ‘cheap’. Ok, here’s what I did. I have a lot of electronics junk. I dug up an old USB web cam from my junk box. Web cams, in fact all digital camera type devices, incorporate an IR filter of some kind. Why? Their image CCDs are very sensitive to IR light. If there were no IR filter all their pictures would look funny, i.e. would look different than we see the world, because they see the IR and we don’t. This webcam, new, cost me about $40. But it was worth nothing today, so I disassembled it, got the lens carrier out, and removed the lens. The IR filter was square, about 12.5 x 12.5 mm, and was glued into the plastic lens holder. Before trying to get it out, I figured to test it first.

Note: The IR filter is blocking IR from outside, getting into the camera. So the side of the filter that faces out of the camera is the side you want to face into the laser. Incase it makes a difference, and I think it does.

So I slid the lens holder over the laser and got out my trusty LaserCheck. If it works, I will get a realistic reading. If it doesn’t, I’ll get a nutsy reading like I did before.


Results

And…it worked! I got a sensible reading! I proceeded to take a series of test readings, at the three wavelengths, with the filter and without:

Wavelength No Filter With Filter
532 nm 401.0 mW 52.1 mW
808 nm 35.4 mW 3.68 mW
1064 nm 64.1 mW 8.16 mW

Well, now this is interesting! At 808nm, the IR is reduced by about 90%. And at 1064nm the IR is reduced by about 87%. It’s impossible to know how much the green is reduced, since we can’t get a good reading of just the green without a filter. But 50mW is still acceptable – a heck of a lot better than a 5mW pointer anyways…?

So, I pried the IR filter out of the webcam’s lens holder and (keeping track of which side was which) I used a little medium-strength lock-tite to affix it inside the aperture cover of the green laser. Now my green laser has an IR filter! Yippee! Now it’s reasonably safe!

Here’s a closeup of the IR filter, glued into the laser’s aperture cap:
IR filter in place

Obviously the IR filter I am using, was never designed to block such intense sources of IR, so there is bound to be some IR leakage. Who knows, the filter might even break down at some point, so I will test it periodically and find out.

But, what about the other problem? The power spike then rapid loss? Well now I can get accurate measurements, so it must be time for another chart:

Initial Peak 125.0 mW
After 5 Seconds 44.8 mW
After 10 Seconds 28.8 mW
After 15 Seconds 16.7 mW

Oh… Uh… Ok. So my 80mW laser has an initial peak of 125mW. Yeah that’s good. That’s why it will burn a match or pop a balloon almost instantly, when first turned on.

The rest of the numbers aren’t so great though, are they? I didn’t bother to test the reading past 15 seconds, I don’t really want to know. I guess the good news is, if I want to let my cat chase the green dot around, I just have to leave the laser on for half a minute first, then it’s probably safe for her to chase after that.

Footnote Regarding the Measurements:
The LaserCheck wavelength setting simply adjusts a ‘formula’ that the LaserCheck uses to calculate power – it does not filter anything. So setting it to 808 doesn’t just measure the 808 light and ignore the other lines, it simply measures everything and assumes it is all 808nm. So the readings are not assumed to be absolute or completely accurate – I have neither the experience or equipment to measure the relative strength of the separate lines. This is merely the best I can do, with the tools and experience I have at home in my livingroom. Your mileage, as always, may vary.


Summary

With the IR filter infront of the laser, the IR ‘halo’ is completely gone now, as visible in these Before and After shots:
IR halo around green dot
IR image: No IR Halo
Both images taken with the DV camera in Nightshot mode, the dot at about 3 feet, after reflecting through a cheap plastic prism (the cause of all the deformation and ‘star’ effects is the prism).

So, not really the great deal I initially thought. The cost of the laser, the cost of the IR filter I had to add, and the final results showing the under-achieving performance, all add up to… yep, that’s right: If it seems too good to be true, it probably is!

I should add: I’m not bitter or angry. I’m not upset at being cheated or ripped off. I took the chance, I bought a cheap laser from an unknown dealer on ebay. I’m dissapointed, but mostly in myself for letting myself get sucked in by the too-good-to-be-true vibes. I also have to acknowledge the educational aspect: it was my first green laser, my first ‘high power’ laser, and it has inspired me to learn quite a bit about DPSS frequency doubled lasers, IR filters, etc.

Save your money, and buy your lasers only from reputable dealers – where there is a warranty, a returns policy, and some level of responsibility.

I’ve shared my experiences with you all, so you can hopefully learn from them, save your money, save your eyeballs, and play safe!


The Fine Print
Information provided on this page is based on my own personal experiences. Although I purchased my Cheap Green Laser at Ebay, I have not identified the individual seller. Outside of the general recommendations given on this page I won’t warn against any specific laser or brand. I suggest laser buyers accept the responsibility of doing their homework before making a purchase, as much as I suggest laser sellers do the same and learn about the products they are selling.

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