What's the trick in focusing a diod in the "Aixiz" housing?

[scriptster]

Hi everyone, my inaugural post here, so to speak.

A complete newbie to the field of laser pointing. In fact, came here with a desire to burn something rather than point at :yh:

I'm trying to rig a CNC table with a laser diode to burn simple line drawings onto wood. Ideally, any type of wood but pine is a must for me. It also happens to be the lightest colored which does not help with heat transfer but it's not too dense either, so I'm hopeful I can find something that works.

What I got is a couple of SONY SLD1239JL-54 visible red 100mW diodes and one Aixiz housing which finally brings me to the heart of the matter: how if the world do you guys focus those?!

I mean, having the safety goggles on does no good because I can't see the light spot. Having them off makes me think I'm going to get blind sooner rather than later. In any case, I can get the spot to a size of maybe 1/16" to 1/8" which actually makes the 100mW diode a hell of a laser pointer but helps me none in terms of actually burning anything: it's still way too big for both the power concentration and accuracy. I get to a point where I can sort of melt a piece black Styrofoam but that's it. Wood does not budge.

I do realize that 100mW constant/180mW pulse power may not be enough to burn wood fast enough for me anyways, but I want to at least get to a point where I can clearly see that my problem is the diode itself (which I'm actually running at 160mW constant with the driver I have) and not just the poor light concentration.

In addition, I may be missing the big picture here: I actually need to focus , not collimate . So can someone please educate a newbie here: does "Aixiz" designation stand for just the dimensions of the housing or also for the type of lens supplied? Are there drop-in replacement focus-able lens available?

And, of course, if someone is willing to share wisdom on how to focus the Aixiz lens without blinding yourself, I'm all ears. I can't even begin to think about focusing an IR diode but I've seen them sold for this housing and I may have to switch to IR due to the demands of the job at hand. For now I just want to be able to focus the red light to the tiniest spot possible.

Any comment will be greatly appreciated!

 

[dr-ebert]

100mW red are pretty borderline for burning. Try a bluray. With a 120mA PHR (90..100mW BR power), it might just work, but would probably be very slow. Getting a BDR at around 350mA plus the 405-G-1 lens (a must for this diode), it should work a lot better, but it's much more expensive as well.

The beam as emitted by the diode forms a cone with an aperture angle of about 10-20 degrees, more like a spotlight. The collimating lens turns this into a thin, parallel laser beam. If you put the lens a bit farther away from the diode, the beam converges to a pinpoint in front of the diode (distance depends on how far the lens has moved away from the parallel = infinity focus point).

These beams can be focused down to maybe a few micrometers. You cannot determine this visually. Even a parallel beam should have no more than about 2-3mm diameter. Try to simply turn the focusing ring slowly so that the spot goes from big to small... until you start to see smoke curling up.

There are two types of goggles: those that block or reflect the laser radiation to nearly 100%, and the so-called "alignment goggles" that only attenuate it by a factor of 100-10000 (Optical density [OD] 2-4). The ones sold as "hobbyist goggles" are the latter, those are the ones you need.

Aixiz here stands for the housing (module) plus the acrylic lens supplied with it. The lens is ok for red and lo-power bluray like the PHR. For higher powers and BR especially, there are better lenses as mentioned above.

 

[LarryDFW]

scriptster;

For CNC work to significant burning,
you will need a couple of watts of IR, lens coupled to a fiber optic cable...,
IR goggles and a lot of caution.

It gets pretty dangerous at that power level.

LarryDFW

 

[Ash]

So can someone please educate a newbie here...edit...on how to focus the Aixiz lens without blinding yourself, I'm all ears.

First, keep your goggles on. When you have it focused, you should see a tiny bright white light (through your goggles) when it's focused on the spot that you are burning.
just an example:

and a diagram:

Basically. With the goggles off, take your axis lens and "un-focus" it (approximately 2 full counter-clockwise turns) until you see a large red spot on the wall.
Put your goggles on. Take the laser and bring it very close to what you are trying to burn until you see a tiny flash of light and some smoke. You probably want to try burning some dark ink on paper first. :thinking:
Oh, and 100mW of bluray will burn pine much better than 100mW of red, and you can get +120mW diodes for around $10 each, add a 405-G1 lens and you'll have some alright burning power (paper, wood, matches, cigarettes, etc) :beer:

 

[scriptster]

These beams can be focused down to maybe a few micrometers.

Well, that's exactly what I'm trying to do ( or get as close as possible to) before graduating to higher power units. Also, last night I bought what was touted as a better alternative to aixiz ( i-Collimator Laser Diode Optic Lens-BURNING-SCROCHER!!! - eBay (item 180379765034 end time Jul-10-09 20:51:05 PDT) ) when it comes, I'll try it out and will report here.

As a side note tho: when you say that the regular stock Aixiz lens should focus if you go past the best collimating point - I don't really see that. I can go from a huge round blob down to a relatively small (like I said, about 1/16" to 1/8" of an inch) with visibly higher intensity in the center, which I cannot assess by size - I's so freaking bright. Well, my guess is maybe 1/4 of the overall light spot diameter. That's the point at which it starts melting Styrofoam, but that's also the best collimating point. If you go past that point in either direction, you are loosing both focus and collimation. Have anyone ever come across an aixiz housing that does not have focusing capability? I mean, mine has lens with surface curvature on the back and the front. My school - level physics is REALLY dusty at this point but I thought you cannot focus it if it has both surfaces curved in the same direction. No?

Anyways, thanks for your comments! I guess, I need to get myself cheaper goggles, too :yh:

 

[LarryDFW]

scriptster;

I'm afraid the lens assembly you bought is too large for the Aixiz housing.

Ideally, a single lens coated for ~650nm will give you more focus power.

LarryDFW

 

[scriptster]

scriptster;
I'm afraid the lens assembly you bought is too large for the Aixiz housing.

Well, that would be a shame. I was under a (possibly wrong) impression that this was a housing itself, so no additional Aixiz body would be needed. When it comes, I'll deal with it, I guess.

By the way, did the first run on the actual CNC today. Even with the focusing problems it does melt through approx. 2mm of black styrofoam (meat packing tray) at 70 mm/min. It is slow but not too painfully so. Did not try wood yet. By the way, CNC use has its own issues - it turns out that I'll need to modify my driver to include an electronic on/off feature - it burns traces where it's retracting to a new path and to the home point. Even badly out of focus there is still enough power in the light spot to leave marks on this material.

 

[dr-ebert]

First of all, in order to focus down to micrometers, the lens has to be less than maybe 1mm away from the focus point.

Then, when you think you've focused down to one or two millimeters, it will actually be much better. But you see a lot of splash around the actual laser beam - scattered light. That's why you need alignment goggles, to let you see only the high-intensity center. You may need goggles with a higher blocking factor (OD 3-4) and maybe even a good magnifying glass in addition to judge the point better.

The usual "manual" focusing rings aren't meant to be used to such precision, at those dimensions the most minimal touch will cause a significant change in focus, and the standard Aixiz lens doesn't sit very tight so it may tilt as well.

There's also the problem to keep the distance constant while tracking if you do get so close. At greater distances, this problem becomes less since the divergence before/after the optimal focusing point decreases, but so does the max possible concentration. You'll probably need to find some acceptable tradeoff.

 

[Ash]

As a side note tho: when you say that the regular stock Aixiz lens should focus if you go past the best collimating point - I don't really see that. I can go from a huge round blob down to a relatively small (like I said, about 1/16" to 1/8" of an inch) with visibly higher intensity in the center, which I cannot assess by size - I's so freaking bright.

Okay. I guess you didn't understand from my diagram above. :undecided:
Maybe this video will help. :yabbem:

YouTube - P1010650

I know th video is a bit dark. But, I was tying to capture the beam so you can see that when the laser light appears as a "huge round blob" a few inches away, it's actually in-focus very close to the aperture. op: