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IR filters, what are they and what do they do?

Carrier X

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Hey guys I am new to the whole laser scene but have always been very interested in expanding my knowledge about them. That being said I was looking around at some potential new lasers and saw that some had IR filters on them and wondered A) What they were B) should I only buy lasers with IR filters? I mean is it a wasted investment if the laser i buy does not contain an IR filter?

Thanks for the information.

-Tucker
 

GBD

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As the name suggests, IR is Infrared.

an IR filter filters out Infrared. This is commonly used in DPSS style lasers, where you have a pump diode (often Infrared) and a crystal that converts it into other wavelenths. The other common one are diode lasers, your violet (405nM) and red (650nM) that is.

most common is green (532nM), there are more expensive and rare ones (473nM for example), but the general idea is to filter out IR output of the laser, and pass only the visable wavelenth. Most common IR pump diodes operate at 808nM, and out of the crystal for the greens I think its converted to higher IR (1064nM) and then finaly doubled to 532nM, visable green. (although some IR leaks by the crystal and is in the output to the lens.
also, if you are not familiar, (nM) stands for nanometers, the wavelenth (from zero cross point to the other end, or peak to peak on the sine wave).
IIRC our visable spectrum is around 380nM (UV) to 750nM (low IR).

It is a good idea to get one with an IR filter, as it is better for your eyes. there has been cases where people's green lasers have stoped working, and they could only see a faint red light, while that faint red light is in the order of several hundred milliwatts. Definatly not something you want to be staring at point blank into your eye.
lasers above 5mW should be considered as an eye hazard, and goggles apropriate for the wavelenths are needed.

So its in good saftey to get yourself a laser with one.
I hope that helped you out understand more, but Im sure there are more people here more knowledgable about this then myself.
Also, a good idea is to browse around the forum more, there are quite detailed threads around with very indepth explanation of all these concepts.
 
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IR Filters remove the infrared light that is left over from the 808nm -> 532nm conversion process through the crystals. IR filters are important when taking into account the advertised power output of a laser, as a laser advertised at 100mw but has no IR filter could very well mean there is 40mW of IR and only 60mW of green light. Its mostly about getting what you paid for.

There are some people who will say that safety is an issue with no IR filter, the argument being that the diffuse reflections and high divergence of IR as it exists your laser can cause damage to your eyes because you cannot blink as you cannot see the IR light, which makes sense, but I have never seen any laser that outputs enough IR (Besides an IR laser :p) that is focused enough to pose any significant risk. It just diverges too quickly.


Helpful?

EDIT: GBD makes a good point about people looking into their laser and getting hit with IR, although ive never read any stories like that, its a good idea NOT to look into the end of any laser.
 

Carrier X

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Awesome thank you guys, this helped a lot I'm glad you guys got back to me so quickly! :)
 

SubrosaNJ

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This thread was very helpful to me as well. I have a question to add on to this. With the example given of a total 100mW if 40mW was IR and 60mW was green, would the laser light a sharpied up match better or worse then a full filtered 100mW green? Why? Or would it really make a difference in that case?
 

HIMNL9

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Some modules have a lot of IR focused in a different way (or also not focused, side-crystal leakage), so no, the "pure" 100mW one will burn better, cause the IR part don't become correctly focused in the unfiltered one.
 

Bobby

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Is there a thread with recommendations for IR filter sources? The "noob definitions" thread referenced them, but I did not see a link. Optotronics seems to have them, but was wondering if there were more options, especially to the point of different wattage filtering ...
 

Bobby

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Cool - 5mm x 5mm for $7, and 10mm x 10mm for $10.

How are they rated? I.e., is there an OD rating, etc.? I did not see that specified...
 

mfo

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As the name suggests, IR is Infrared.

an IR filter filters out Infrared. This is commonly used in DPSS style lasers, where you have a pump diode (often Infrared) and a crystal that converts it into other wavelenths. The other common one are diode lasers, your violet (405nM) and red (650nM) that is.

most common is green (532nM), there are more expensive and rare ones (473nM for example), but the general idea is to filter out IR output of the laser, and pass only the visable wavelenth. Most common IR pump diodes operate at 808nM, and out of the crystal for the greens I think its converted to higher IR (1064nM) and then finaly doubled to 532nM, visable green. (although some IR leaks by the crystal and is in the output to the lens.
also, if you are not familiar, (nM) stands for nanometers, the wavelenth (from zero cross point to the other end, or peak to peak on the sine wave).
IIRC our visable spectrum is around 380nM (UV) to 750nM (low IR).

It is a good idea to get one with an IR filter, as it is better for your eyes. there has been cases where people's green lasers have stoped working, and they could only see a faint red light, while that faint red light is in the order of several hundred milliwatts. Definatly not something you want to be staring at point blank into your eye.
lasers above 5mW should be considered as an eye hazard, and goggles apropriate for the wavelenths are needed.

So its in good saftey to get yourself a laser with one.
I hope that helped you out understand more, but Im sure there are more people here more knowledgable about this then myself.
Also, a good idea is to browse around the forum more, there are quite detailed threads around with very indepth explanation of all these concepts.
False.

Having an IR filter does not make the laser "better for your eyes". The IR in a dirty laser is less than the amount of visible light being emitted from the aperture. As mentioned by spyrorocks, the main purpose of it is to say you're getting what you paid for which would be the visible light, not a combination of visible light + IR (although trace amounts of IR will exist in DPSS no matter how good the IR filter is).
 

mfo

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I know of two places to buy IR filters cut for lasers:

NovaLasers IR Filter

and my store, Radiant Electronics

Radiant Electronics IR Filter

If anyone else knows of any other places please let me know...
Your store is pretty dope, never knew you had one. I was checking out your optics and I was wondering, would you ever be able to sell Reflect Blue Pass Red/Green Dichroic Mirrors? So I could use in RGB.
 
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Hey mfo,

Possibly, if we could find a good source for them. I run the store with MarioMaster, if you'd like to inquire about a new product shoot him a PM with the details and we'll see if we can work it out :)
 

GBD

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False.

Having an IR filter does not make the laser "better for your eyes". The IR in a dirty laser is less than the amount of visible light being emitted from the aperture. As mentioned by spyrorocks, the main purpose of it is to say you're getting what you paid for which would be the visible light, not a combination of visible light + IR (although trace amounts of IR will exist in DPSS no matter how good the IR filter is).
Thanks for the correction, Im still learning myself. :beer:
On the subject, is an IR filter a universal device (If assuming its appropriate for the IR wavelenth) that will only block IR and pass a visable wavelenth?
(meaning can it be used for other DPSS style lasers, 473nM etc)?
or must you get one that was made for a 473nM system?
 
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mfo

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Thanks for the correction, Im still learning myself. :beer:
On the subject, is an IR filter a universal device (If assuming its appropriate for the IR wavelenth) that will only block IR and pass a visable wavelenth?
(meaning can it be used for other DPSS style lasers, 473nM etc)?
or must you get one that was made for a 473nM system?
The IR filters work for a certain wavelength range if I am not mistaken. The ones used in 532nm greens cover the two ranges needed to make green which is 808nm and 1064nm. For blue, you start out with 808 also, then 946nm and finally 473 so I do believe the same IR filter would work since the 473 DPSS uses a shorter wavelength range, although I could be wrong :p
 
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False.

Having an IR filter does not make the laser "better for your eyes". The IR in a dirty laser is less than the amount of visible light being emitted from the aperture. As mentioned by spyrorocks, the main purpose of it is to say you're getting what you paid for which would be the visible light, not a combination of visible light + IR (although trace amounts of IR will exist in DPSS no matter how good the IR filter is).

man, all this is confusing. basically an ir filter is just to make your laser light seem brighter to the eye?
 




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