What type of lens/housing is best for cutting with IR diode?

[scriptster]

Hi all, I've used some great advice on these forums before, looks like I need more.

I am getting ready to upgrade my CNC laser diode cutter ( some more info, pics and videos here: Laser Cutting DIY ) from 200mW red to 1W 808nm IR diode and I need a new housing because the new diode I have is 9mm and the old was 5.6mm

I've already ordered the 9mm version of O-Like's housing (so much better than Aixiz, BTW, at least for my purposes) and, while the package from China is somewhere in transit, I'm looking for ways to improve the optics. In fact, if I need an altogether different housing for a better lens, I'll change the housing, too.

From playing with the AixiZ and the 5.6mm O-Like housing and their respective stock lens, I know that focusing is the major hurdle and from what limited understanding of macro optics I have, I gather that these lens are actually collimating (and one can hope the proper 3-element ones, at least O-Like's seem that way) and not focusing i.e. designed to collect light from a divergent source like the laser diode and send a parallel (not converging) beam of a particular size, something like 0.7mm-1mm beam diameter if what I've red on the Net is true.

What I'm actually looking for is a type of lens that would collect, then converge the light to a focal point that's not actually too close, a few inches at least else the cuts are going to be concave. I mean, they always are, to a degree, but the more straight (vertical) they are the better. And the size of the hot spot needs to be much smaller than 0.7mm. I'd say getting it down to 0.1mm would be great for the types of cuts I'm making.

So, it appears that I may be able to get away with a simpler, convex lens that should also end up blocking less light.

Is my logic here correct or am I oversimplifying things ?

Can someone recommend a good off-the-shelf housing/lens that would work specifically for cutting with 808nm IR diode in 9mm packaging?

Thanks for all your comments and suggestions!

S~

 

[Pontiacg5]

A 9mm diode is going to have a multimode output, it's a square dot instead of a round dot. It's not exactly the best choice for a laser cutter for a bunch of reasons.

808nm is not far enough into the IR spectrum to cut a wider range of colors, as your website suggests.

I would suggest Jayrob's red single element lens. It should boost the output a little since it's a single element. No need to waste power on multiple lenes going for the best divergence when you really just need a strong focal point. Jay's lens should put the focal point far enough out that you won't get the "cone" effect of the beam diverging again, at least in thin materials.

I suggest that you swap to a 445nm diode. Although it too is multimode it is nowhere near as bad as the output of a IR diode. It will also cut lighter materials a lot better, plus you could potentially get 1.5-2W of power through some fairly cheap optics.

 

[scriptster]

Thank you, Pontiacg5.

It looks like I may actually try several types of diodes, including the 445nm that you've suggested. At some point maybe even skipping to the 2W+ modules - I've seen LaserLand's on ebay being sold with drivers, maybe I'll eventually end up with one of those.

But for now the 1W 808nm IR diode has a great advantage over any other type - I already have it. I'll be trying to squeeze as much usefulness from it as I can, and then move on to other types.

Thanks again for your great suggestions!

S~

 

[Bionic-Badger]

You can try one of these, or these.

If you're buying from O-like you might want to pick up one of the 405nm housings + lens too, in case you want to try using a 12x 405nm laser or a 445nm for burning in the future. It'll save you time and money to get them at once.

 

[scriptster]

re-directing this discussion to talk about better wavelength

Thanks, Bionic-Badger. I'm already getting the O-Like's 9mm housing and have just ordered Jayrob's red lens in hopes that they are better than O-Like's because they are one-element.

I've also looked at Meredith's and decided against it (although being able to use both 5.6 and 9mm diodes is nice). It comes with 3-element collimating lens and I'm trying to simplify lens 'cause I don't need a collimated beam. Also, it's a flat cylinder whereas O-Like's housing has those little ribs that will serve as a heatsink.

If you're buying from O-like you might want to pick up one of the 405nm housings + lens too, in case you want to try using a 12x 405nm laser or a 445nm for burning in the future. It'll save you time and money to get them at once.

I'd like to pick up on this and ask an additional question here. Given that it's the second advice out of two I've received so far to use blue (405 or 445nm) diodes for cutting, I wonder if there has been a commonly accepted rationale for why this wavelength is better.

Basically, all I've seen/read about regarding laser cutting revolves around IR or near-IR lasers. Maybe it's because this is all that's available out there in the world of 1KW+ lasers (CO2) and this is not the case here in the single-Watt arena. And that would be a fair assessment, but I just can't see if there is any physical reason for the blue ones to be better. Also considering that they are significantly more expensive that comparable wattage IR ones (probably only because IR ones are so much more common).

Being better for cutting in my mind has everything to do with heat transfer from the beam to the material. I've also seen that the color of material has great effect on cutting. It has to absorb as much light of the wavelength thrown at it. There is no chance to cut a red material with a red laser - it does not even melt whereas the same black material (talking about craft foam, of course - the only thing that cuts at this power level) cuts nicely.

I would think that no material color would make much difference for an IR beam because all would absorb it. Can someone see why this wouldn't be a fair assumption?

Suitability for cutting has something to do with ability to focus, too. And I can see that blue, having half the size of the wave of IR's is probably better suited to minute focusing but, given the tolerances of the setup, I'd be happy to achieve 1/100th of the accuracy possible (shooting for 0.1mm beam size at focus point), and so 2 times a difference would not even register, I think.

Is there any other important consideration I missed? I would appreciate any comment!
Cheers!
S~

 

[Pontiacg5]

808nm is simply not far enough into the IR spectrum to cut any better than a red laser. It would probably help you to think of IR as a very very deep red, in fact at 1W you will probably see a very dim red spot when you focus your laser. I would be willing to bet that you won't be able to cut any additional colored material with the 808nm laser as you did with the red laser (red, orange and most likely yellow for example.)

CO2 on the other hand works a lot deeper into the IR spectrum, and it is more of a beam of heat than light. You just can't compare the cutting abilities of CO2 and IR, they are nowhere near the same. CO2 "sees" almost everything as opaque; glass, plexiglass etc. 808nm light will pass right through all of those things as if it was transparent, and it can't do any cutting if it's just passing through!

You're 100% right when you say that transferring the power of the beam to what you are trying to cut is the main intent when picking a wavelength, and that is why 445 is superior to 808 as far as cutting. 445 is very close to the ultraviolet end of the spectrum, and a lot of materials that don't "look" like they would absorb the beam actually do. (white paper, for instance. Wood burns a lot better with 445 than red or IR as well.)

Blue can also focus to a smaller beam size than red or IR, but as you said with the tolerances you are playing with it's not really a concern. I do believe that you will be able to focus a 445 diode easier than a 1W IR diode though, solely because of the output of each diode. Blue lasers also "carry" more power than an IR laser does, but I think at the power levels most of us play with that does not effect cutting too much.

How big is the head on your cutter? There's no reason you can't have an IR and a blue cutter

 

[scriptster]

808nm is simply not far enough into the IR spectrum to cut any better than a red laser.

Thank you, Pontiacg5. You make all goods points. I know what you mean by not far enough into IR range. I'm actually a fiber optics tech in previous life and more familiar with 850nm near-IR and yes, I can see the end of multimode fiber energized at 850nm as a dim red dot, and one can assume 808nm would be even easier to see.

:tsk:This is not a safe work practice!:tsk: , if anyone new to fiber optics is reading this, by the way.

So, yes, I am convinced, I am going shopping for a 1W 445nm laser diode! What's a good deal on those these days?

How big is the head on your cutter? There's no reason you can't have an IR and a blue cutter

Great idea, too. The Z axis was designed to carry a nice size router (larger than Dremel) so attaching two diodes to it would not be a big deal at all. I might try to do just that for comparative testing.

 

[Pontiacg5]

The going rate seems to be somewhere between $40 and $60, depending on how long you want to wait to get it.

Senkat_Stonetek had a deal going a while ago, I'm not sure if that's still going or not. I know DTR sells them too. Both are very reputable members and know what they are doing when harvesting the diodes.
There are a few others doing group buys for cheaper prices, but you have to wait a while to actually get the thing.

If you get the chance you really should try playing with a CO2 laser. I built one a while back and it's really a very cool laser and wavelength. They get expensive, especially with the special ZnSe lenses you need to focus the things.

Good luck with your build, I'd love to see some videos of the completed project!

 

[Bionic-Badger]

There are other reasons for choosing shorter wavelengths. Many surfaces don't absorb near-IR (NIR) very well. For example, here is what the world looks like in NIR. This was photographed using an IR-pass filter that blocks all visible wavelengths:

Notice that it doesn't look all that different than a black and white photo. However, some surfaces, like the photos on the wall, actually reflect NIR far better than shorter wavelengths. The bottle to the right of the Tabasco bottle has a green nozzle, and red sauce, and yet both reflect NIR about the same.

You might want to do some investigations into which wavelengths are best absorbed by the materials you wish to cut. Looking at some foam like in the video you posted, using the NIR-modded camera, it seems to quite reflective of NIR, but then my foam is yellow. I honestly don't know if shorter wavelengths would be any better.