IR filter

[Av8or]

Hi

I bought the Dealextreme 5mw laser pointer (DealExtreme: $7.15 5mW 532nm Green Laser Pointer Pen with DX Logo (2*AAA)).

I know this may put out around 5-10 MW (HOPING FOR 5, not a ton more), but do i need an IR filter for the 5mw power (assuming ur not an idiot when it comes to lasing yourself directly in the eye). I will sometimes shine my red laser (<=5mw, IIIa) on a mirror and have it reflect on to the ceiling, but i don't lase myself in the eyes. Is it safe to do that w/ a 5mw green, w/o an IR filter? The IR should maintain coherence with the green beam, so if u don't lase ur self w/ the green beam than the IR shouldn't get u, right.

IF it's a last resort to get a lower power (i.e. if it's way overspec from 5mw), is it possible pot mod a green to a LOWER power?

Thx

Av8or (no, that does not mean i will use this anywhere near a plane, know that's just idiotic and downright evil).

 

[Arshus]

At 5-10mW power, a reflected/refracted beam should do little dammage. At such a low power, I wouldnt worry about the IR comming from that thing either.

-Sal

 

[Leodahsan]

don't listen to arshus. These pens output 5mW of green and have been tested to >25mW of IR: thats perfect to damage your eyes.
Just don't point it. If you want a filter, open a old webcam that does not detect IR (test it with a remote control, search the forums, some cameras have it), remove the filter and glue it on the pen. Just don't try to open if you like the aesthetics.

 

[anselm]

Don't listen to Leo either, an IR filter for a 5mw is overkill.
The IR diverges rapidly, it's not focused like the green beam.
The trouble with IR is:
say you have a 200mw green that has 150mw green plus 50mw of IR, just as an example.
Then you have your safety glasses that block the green but not the IR.
That's when you have a problem, when you think you are safe, but in reality aren't.

Leo's tip to obtain a filter is good though.

 

[Leodahsan]

lol @ anselm, if he is asking for an IR filter, he's probably uncareful and is worried about the risks (probably he got the laser on his eye, and search the internet and saw IR and blah blah..)
it is behind the lenses, it is collimated too. People have tested they to have 25mW of IR (australian customs test it too )

http://laserpointerforums.com/f52/laser-review-boblaser-com-700mw-532nm-handheld-laser-60249.html

search for (ctrl+F) "Yes - that is a little eclipse of IR right there."
that is 700mW: but uses crystals and lenses, just like chinese lasers.



edit: are you stalking me? lol @ anselm

 

[RA_pierce]

How much infrared leaks, how it diverges, the power of the green, and all that...
It depends.
The only way to know is to test your laser.

I've modified and repaired lots of greenies including the DX Newwish pens.
I've personally tested the IR output and the green output in terms of power and divergence.

Generally (not always) the IR from these pens is around 20-30mW. It comes out in a splotchy mess of a beam at 2-3mRad.
I have seen these output anywhere between 0-40mW of green. On average, the green will be 7-10mW - average over 1 minute.
The power is usually inconsistent and dependent on temperature.
IMO, modifying these lasers for 5mW is pretty much futile, since they can vary so much with temperature.

This laser can be modified easily to output a lower power (simply disassemble and turn the potentiometer). Doing this not only decreases the green output, but the IR output as well.

Regarding the IR... Filters can be found online (I believe radiantelectronics.org has them).
The only time you will be exposed to IR from this laser is if you are exposing you eyes/face to the green as well.
The first safety mechanism is the finger that presses the button. Keep that in mind.

If you really want a laser that outputs exactly 5mW of green and not 30mW of IR (no modification required) shop at Z-bolt.com.

 

[Leodahsan]

IMO the first safety mechanism is to not point at face/eyes/living things/vehicles.
IR filters can be bought from rayfoss @ 3usd a piece

 

[Arshus]

How can a pen that meters 5-10mW have 25mW of IR? Doesnt the meter meter TOTAL output? Or do you guys mean just a random Ebay pen that may be overspec?

And also, I heard you really should have an IR pass filter (not an IR blocking). These can be bought at camera store and such, you just ask for an R-72 IR pass filter. Those cheap green colored IR filters generally let a fair amount of IR along with the green.

-Sal

 

[anselm]

And also, I heard you really should have an IR pass filter (not an IR blocking).

And then do what with it?:thinking:
Measuring the actual IR, assuming the filter would block the green?

 

[Arshus]

And then do what with it?
Measuring the actual IR, assuming the filter would block the green?

Yeah, I got that advice from jack at opto re: how to properly measure IR.

And btw, my bad on the 1st post didn't see he bought a DX pen. In my mind I thought I was an already metered 5-10mW pen. I agree, most of the greens I get from IQS have anywhere from 15-30% IR.

-Sal

 

[RA_pierce]

When measuring for IR, I use an IR filter that blocks 99.9% of 808nm and is AR coated to pass 98% of 593-473nm. Not a "cheap" filter.

 

[Leodahsan]

You need to know the actual loss of the filter too. Some block 1% of green and blue light so, if you need ACCURATE (I say.. 0.1% accuracy) you will need two filters. If they are 99.9% certified as RP said, you do not need the test tho.

@Arshus
DX says: 5mW
Meter says: 29mW
Eye says: not 29mW of green, 5mw at most
Brain says: 24mW of IR
Australian customs says: You shipment has been seized. Laser test: 29mW

 

[Arshus]

Hey RA, how accurate do you think an IR reading would be on a beam being filtered though 532 goggles?

@leo: lol yeah the only thing DX is right about is 5mW of green.

 

[Leodahsan]

The accuracy of the IR reading can be calculated by the VLT IMO. if the goggles are 50% VLT so the IR reading will be 50% lower.

BUT... VLT means visible light transmission (I think it is transmission) so IR could not be there so.. check your manufacturer's glasses datasheet/specs sheet for further info.

 

[RA_pierce]

Hey RA, how accurate do you think an IR reading would be on a beam being filtered though 532 goggles?

@leo: lol yeah the only thing DX is right about is 5mW of green.

The accuracy of the IR reading can be calculated by the VLT IMO. if the goggles are 50% VLT so the IR reading will be 50% lower.

BUT... VLT means visible light transmission (I think it is transmission) so IR could not be there so.. check your manufacturer's glasses datasheet/specs sheet for further info.

Well, the only way to find out is to find out.
I could give an estimate based on my gut, but that would just be a guess.

When it comes to measuring the power of a laser, an LPM is needed. There isn't really a way around it.

But, I think if you are just looking for a number that is close and not too precise, filtering out the green with some good goggles should be ok.
I turned my only IR laser into a greenie so I can't measure with my goggles, otherwise I would.

 

[Arshus]

Well what I'm talking about for example is when I point a laser at my Laserbee and then put my glasses in between the aperture and the thermopile, so the beam has to go through the glasses on its way to the thermopile. In theory, this should filter out green light and any readings the LPM subsequently gives would be heat generated by something other than 532nm light, in this case, probably IR light.

For example, I did this with my O-like 400mW green laser, and got the above output plots. The left is an output plot of the laser's total output, and the right is a plot of the laser's output filtered by the 532 goggles. As you can see on the right there is a peak of 30mW on the IR plot. If the laser's peak on the total output graph is 530mW, then:

(30/530)*100 = 5.66% IR?

The question is: Is this meaurement accurate for the purposes for determining how much IR the laser is emmiting?

Thanks,

Sal