IR danger? Power meter tests and Pictures!

[RA_pierce]

Whether or not IR is really dangerous has been a question that has been debated many times before.
My goal here is to clarify the issue with facts.

For this I used my Laserbee I to test the power of the IR leakage emitted from a very common type of green laser used today, the O-like 150mW module. The Laserbee I is a thermal power meter, so the power measurement is not affected by wavelength.
The tests were done with 1.2V NiMH batteries for lower power levels closer to 100mW. I thought this would be a good "in between" measurement to cover some lower power greens and also the medium power greens.
I used my cellphone camera to take the images in which the IR is visible.

Note: The Laserbee I can only read down to 5mW, so when it reads 0mW, the total power can be no greater than 4.99mW.

The results are below.

I hope these results will help clear some of the fog around the subject.

I would have liked to do these tests with several different lasers but this was the only unfiltered one I have at the moment. If anyone else has more information, please feel free to contribute.

EDIT: I would like it if this could be stickied either here or in the General section because I think this could be helpful information for n00bs and some older members alike... I just don't know how that gets done...

Thanks all for reading.

THUMBNAIL:

 

[Jaseth]

Very nice, this will no doubt be of great help to many!
Thank you!

Seb

 

[Benm]

I am affraid these measurements still are only valid vor the very specific laser you tested. In general, it is very hard to say how much IR any dpss laser will leak, and to what extend this is collimated with the green beam.

Conceptually, it is not likely for the IR leakage to be collimated with the green at any distance, with the IR often coming out at much greater divergence and hence reduced risk.

The problem is you cannot safely assume this to be so for each and every dpss laser on the market.

 

[RA_pierce]

I am affraid these measurements still are only valid vor the very specific laser you tested. In general, it is very hard to say how much IR any dpss laser will leak, and to what extend this is collimated with the green beam.

Yes, however, with all of the green lasers I have owned, the IR leakage is almost exactly as is described here, where the divergence is much larger than that of the green output, but still well collimated in comparison to an LED, for example.

Conceptually, it is not likely for the IR leakage to be collimated with the green at any distance, with the IR often coming out at much greater divergence and hence reduced risk.

Not sure what you mean here... that's exactly what my results illustrate...

The problem is you cannot safely assume this to be so for each and every dpss laser on the market.

Of course not, that is why I was hoping others might have some information of their own to contribute to get a more complete answer to whether or not IR leakage is anything to worry about.

 

[lasersbee]

I am affraid these measurements still are only valid vor the very specific laser you tested. In general, it is very hard to say how much IR any dpss laser will leak, and to what extend this is collimated with the green beam.

Conceptually, it is not likely for the IR leakage to be collimated with the green at any distance, with the IR often coming out at much greater divergence and hence reduced risk.

The problem is you cannot safely assume this to be so for each and every dpss laser on the market.

By the Photos I can see that the tests were performed very close
to the LaserBee I Thermopile sensor and any divergence of the
IR beam would have been minimal at that distance...
unless you are saying the IR beam of a 532nm Laser is greater than
30 degrees...
(In my personal experience the IR beam of any tested lasers in the
shop has been below 10 degrees)

Agreed... I have not personally tested every green DPSS laser on
the market...


Jerry

 

[ZRTMWA]

Wow great post! Nice pics too! I actually made a thread about IR and O-like modules a couple weeks ago, billg519 graciously tested his:

http://laserpointerforums.com/f45/amount-ir-o-like-modules-47319.html

 

[RA_pierce]

By the Photos I can see that the tests were performed very close
to the LaserBee I Thermopile sensor and any divergence of the
IR beam would have been minimal at that distance...
unless you are saying the IR beam of a 532nm Laser is greater than
30 degrees...
(In my personal experience the IR beam of any tested lasers in the
shop has been below 10 degrees)

Agreed... I have not personally tested every green DPSS laser on
the market...


Jerry

Yes, in order to collect all of the IR on the sensor, the readings had to be taken pretty close. With the collimating lens removed, the divergence angle was >15 degrees.

ZTRWMA: Thanks, that helps the cause. Hopefully we can get more info compiled.

 

[Benm]

Of course not, that is why I was hoping others might have some information of their own to contribute to get a more complete answer to whether or not IR leakage is anything to worry about.

I am interested in the complete picture too. I have never encountered any green laser that had a narrow output of IR - at least compared to the green. The green comes out with divergence in the order of 1 mrad, the IR in the order of several degrees - so it does spread out over a great area at a distance of a meter (or foot for that matter).

One interesting aspect is that there are 2 IR frequencies to worry about: 808 and 1064. By practical construction i dont see much of a change of the 808 being collimated with the green, but the 1064 is another matter.

If the laser uses intra-cavity doubling or the doubling crystal mounted straight to the 1064 nm solid state laser, i would expect the 1064 to be collimated reasonably well with the 532. This would only pose a problem if the doubling process is rather inefficient and not intra-cavity.

One problem is that it is hard to check for 1064 nm leaking specifically. Digital cameras may still be able to see 1064 nm, but how can you tell it apart from 808?

 

[lasersbee]

One problem is that it is hard to check for 1064 nm leaking specifically. Digital cameras may still be able to see 1064 nm, but how can you tell it apart from 808?

Perhaps by using a filter that specifically filters only 808nm or 1064nm
and using an IR sensitive camera in conjunction with a 532nm specific
filter....

Jerry

 

[Benm]

Sure, that would be perfectly feasible if you could find such a filter.

If you could devise a setup that would block both 808 and green but passes 1064, it would at least be possible to make some measures as to how much 1064 actually comes out.

My gut feeling says it will typically be very little since the doubling is (as far as i know) always done intracavity nowadays, with HR-1064 coatings on either end of the 2 crystal assembly. Still, i am curious to how little 'very little' actually is

 

[LSRFAQ]

A littrow prism, brewster prism, or a diffraction grating would solve this nicely. You have to watch, black and white ccd cameras have great response at 808 nm, but very poor response at 1064, are down to half response at 1100 nm, they have almost no sensitivity at 1.2 microns, and nothing at 1.3. So You need a IR viewing card or a good high gain camera to see the 1064. Mid IR cameras do exist, but are beaucoup dollars.

I'll let you in on a secret, most older green phosphors of the zinc sulfide variety have their light quenched by bright IR from 700 nm to 1200 or so, the IR shows up as a dim spot on the glowing green phosphor. The ZNS stuff from Post Apple has worked for me in the past. You coat it on a card using clear flat krylon spray paint, then dusting the wet card with powder.. You pump it with a UV or deep blue lamp or led, and hit it with the IR. IR is clearly visible as a dim spot. Newer blue or green ceramic phosphors from ebay do not work at all. Ie the Strontium or Cerium YAG ones, do not work, although we have seen the effect weakly on a orange yag phosphor from one company.

Reagents - Zinc Sulfide

These work better, are inexpensive, and known to cover the 1064.

http://www.thorlabs.com/thorProduct.cfm?partNumber=VRC4D05

Here are low cost gratings:

http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=1490


Steve

 

[Benm]

If they are sensitive from 700 to 1200 nm, how do you tell the effects of 808 and 1064 apart?

To do the measurements required, you'd need a high pass filter in the 900-1000 nm range to make it work. A grating could work to accomplish such separation just fine, only leaving the problem to obtaining a camera with known 1064 response.

 

[LSRFAQ]

If they are sensitive from 700 to 1200 nm, how do you tell the effects of 808 and 1064 apart?

To do the measurements required, you'd need a high pass filter in the 900-1000 nm range to make it work. A grating could work to accomplish such separation just fine, only leaving the problem to obtaining a camera with known 1064 response.

With a transmission grating, you'll get a 0th order, where some of the beam passes straight through unmolested, in the center.
808 will be closer to the 0th order then 1064. The weaker second and third (and so on) orders will repeat with 808 closer to the 0th order and 1064 outwards. If you run the grating in Raman-Nath mode, you'll get spectra on either side of the 0th order.

A 110Vac neon lamp or IR has IR lines as well as visible, and a neon lamp is going to set you back all of 2$ for a pack of two at radio shack.. Remember to use a ballast resistor if you buy a bare , unpackaged lamp or led... If you google neon spectra many line tables will pop up. A few minutes at digikey, mouser, or electronic goldmine etc will find you IR leds with known center frequencies. LEDs tend to be wide, 20-40 nm wide, but have a strong peak to their spectrum.

supercircuits.com sells low cost IR NTSC cameras.. Remember NTSC?? Its that thing before digital TV, but most digital TVs and many frame grabbers still have NTSC ports.

No laser experimenter should be without a grating, anyways.. Its one of those useful things to laminate and put in one's wallet.

This guy sells filters, bandpass, edge pass, high pass, low pass, dichroic combining, laser line, you name it, he usually has some neat surplus from his company on ebay:

eBay Store - BJOMEJAG EBUYER STORE: Dichroic Beamsplitters, Fluorescence Emission, Fluorescence Excitation

setting up a reflection grating with two slits to make a monochromator is not hard either.


Steve

 

[Benm]

A slit and grating approach could indeed work for telling the wavelengths apart. I've never seen it demonstrated on a practical dpss laser as a method of testing, but it is perfectly viable to set up.

You might have to remove the IR filter from the camera to get it too work though. Even the cheapest of webcams will have some ir filtering in place to prevent totally odd looking images from coming out. 808 may not be filtered well because its very close to what should be visible, but 1064 is a fair bit further away.

 

[LSRFAQ]

One nice thing about Supercircuits' 20$ little camera, a IR filter is NOT included.

Gratings work great with multiline lasers, and the 808, if there, should really be a diverging blob right at the end of the laser, while 1064 should be pretty close to a decent beam, but defocused a bit, unless its a very expensive laser with a achromat as the collimator.

Steve

 

[Things]

I have found with cheap green lasers today that the crystals and lenses are usually so small (To save money) that any IR within the unit is probably lost before it even comes out of the laser.

TBH, IR is overrated in green lasers. What I think scares most people is they can't see it, but you will be fine as long as you DON'T shine your laser right into your eye! If you are shining it into your eye, you have more than IR to worry about!