Laser burning - what's my problem?

Hi,
As there's no newbies forum, I'll just dive in here. Sorry if it's all a bit basic - it's not for lack of googling!

1: I want to burn... YouTube is full of people making smoke, engraving black plastic etc, as if it's no problem. I'm experimenting with an LPC836 with an Aixiz (?) coated lens... NOTHING! Focussing isn't easy, but I turn the driver down for that, then up again. I'm using a lens-->paper distance of about 6" (15cm), hoping that the focussing's not quite so delicate?, but still nothing.

2: I HAVE managed to make a tiny mark on some thermal paper using a dvd burner diode in its sled, trying to hold the paper a couple of mm from the lens, but focussing is VERY delicate.
(2a: Has anyone had any luck using the auto-focus mechanism of a sled?)

3: I've deduced that the meaning of "LED" is "became an ex-diode", but what does it stand for? : - )
Thanks for any help!

First, what colour is the paper? Have you tried things like black balloons or black electrical tape? White things don't burn as well - white doesn't absorb the light nearly as well.

Do you know what current you're running the diode at? You should be using a test load to adjust the driver. Once you have it set and have the diode hooked up you're best not to readjust it without using the test load, especially if it's running. That has been known to kill diodes.

You should be able to see the focal point fairly easily, that's where you want whatever you're trying to burn to be placed.

Don't use the sled.

LED stands for "Light Emitting Diode" - when a LASER diode dies, it sometimes turns into what's essentially an LED due to damage to the laser cavity. The die may still emit light, just not laser light.

Are you wearing laser safety glasses that attenuate the wavelength you are working with?

You can see the focal point at full power very well with your safety glasses on, they make a big difference in getting a proper focus and as a bonus they preserve your eyesight.

Are you sure you have gone above the Laser Threshold
current and your Laser is in fact Lasing ???

Jerry

Hi and thanks. The paper is white, but I've also tried blackening it with charcoal, no difference.
Also, a piece of wood painted matt black, no difference.

I'm using a switched driver unit that gives constant currents from 15mA to 450mA. I turn it up to 200 for attempted smoke-making.

I'm curious as to why not use a sled - it's the only one of the two that's done anything so far! : )

Ah, thanks for the LED info. I was thinking it stood for something like Lifeless Ex-Diode : - )

The enclosed pic (if I CAN enclose one) shows an aspect that no doubt doesn't help, but I don't know what to do about it...

Cheers,

PS: In the pic, the line is about 4mm end-to-end.

I think that's dead. I LED'd an oclaro 700 and it looked just like that. It's also quite dim. A functioning diode would wash out the image more than that.

Hi, thanks but maybe not.... I reduced the current to about 80mA to get a clear picture. Here's two more at 340mA, one on wood painted matt black, and one on white paper.
Apparently (from another thread), the "wings" are normal for this diode, and don't take much of the energy. So why isn't it burning?? (
Thank-you,

GrahamRounce said:

Hi, thanks but maybe not.... I reduced the current to about 80mA to get a clear picture. Here's two more at 340mA, one on wood painted matt black, and one on white paper.
Apparently (from another thread), the "wings" are normal for this diode, and don't take much of the energy. So why isn't it burning?? (
Thank-you,

Click to expand...

Have you actually turned the focus knob/lens to focus it to a point?

What kind of burning are you looking for or expect?
As I only have one strong red, a LPC-826, kinda the little brother to the 836 "thanks Alaskan for the chart on the other thread" at 375mw.
Members help me on this as its a nice match lighter but I really can't smoke a popsicle stick and can get some smoke on a black CD case and melt some electrical tape.
Ok its in a small pen light host from Pman so I can't run it long.
Is the OP expecting to much?:undecided:

Maybe I am. Btw, thanks to all for the helpful suggestions. I've worked out part of the problem. I was running the switched driver from 6v. As the LM317 spec says it must be at least 3v over the load voltage, I thought it would be ok. I'd only tested it with just the multimeter current range as the load, figuring that "constant" meant constant! When I double-checked with the actual laser load, the current was drooping a lot at the higher end. I've now got it running off a 9v adaptor, and the current is what it should be.

Still, though, it refuses to mark paper, either white, blackened or thermal.
But with the current at 340mA (220mW) it WILL, yay, evoke a small wisp of smoke from electrical tape, the melting just visible on the surface.

I must admit I'm disappointed. I expected thermal paper to be marked, smoke to come from blackened paper, and less but still some smoke from white paper. Do you have to go up to >1W for that kind of thing?

If you look at the specs for a dvd burner, it writes with a power of "6mW - 45mW", and burns the dyes reliably at high speed. Surprising, no?
Thanks again,

What are you using for a lens? I have a acrylic on mine and haven't tested any type of glass yet. I'm also not sure if my rated 375mw was with a G2 when Pman measured it.
Which would sure help.
Have you tried to focus it out of infinity and get the sweet tight spot a few inches away from the laser head before it expands?

Hi - This is the lens:
AixiZ Red Laser Glass Lens 635-670nm, AixiZ
...and the setup is in the pic. The holder holds the lens loosely, so it's not easy to adjust it finely. To focus, I switch down to 80mA, then focus the lens as well as I can, then move the target back and forth for the sharpest image. Then crank it up to 340mA for burning.

Hi Graham, do you have an internal spring behind your lens, because without some tension behind the lens, it will be very hard to focus properly.

Edit: This is a pic of a lens holder, internal spring, and module (1st pic) from DTR's store.
You can also use an external spring, or use teflon tape wrapped around the lens threads.

Yup what Bowtie said but if you do any type of experimenting with springs you might have laying around which can work at times, be careful as that's an open can diode with everything exposed.

That's why in most cases IMO, teflon tape is a distant 3rd place option; if you're not careful, any stray or loose piece of teflon may get on your lens, or worse yet, on the diode in which case it's toast!