Easiest way to make a laser burn

Ive always been fascinated by lasers they are just such neat devices, the only problem is after a while you get a little bored just shining them at things. I always wanted the 007 laser that will just slice through anything, while this instructable wont give you that but it will let you easily slice through the black trashbag or electrical tape that Dr. No has tied you up with. All you need to be able to do it is a cheap 5mw laser from ebay and a small lens.

Dont expect crazy amount of power from this just enough to make dark plastics smoke, pop dark balloons from close range, and maybe if youre lucky light a black match.

Step 1 How it works

Seeing this diagram might help you understand why a lens will seemingly increase the amount of power a laser puts out. Its clear that it doesnt actually increase the amount power it just focuses it at a specific point, this is one drawback to this burning method because your laser wont behave like a normal laser point after this because past the focal point your beam will diverge, acting more like a flashlight. This is why I wanted to make my lens attachment removable so I can go back to a normal laser pointer whenever I want to.

Which laser to use? In my experience the best bang for you buck is to get the 405nm blue/violet laser not only does it look awesome, change color when it hits light colored clothing, and light up glow in the dark objects, but according the second diagram because its wavelength is shorter it also has higher energy than the other two. However another thing to consider is the mW's your laser produces I believe given the same mW a violet laser will burn the best but a 40mW green is probably more powerful than a 5mW violet. Its really up to you, what you have, what you want to do with it, what you want to spend, and whats legal where you live. I found all three of my lasers for $15.00 on ebay so decided to try all three.

Comments

[Caleb Nehrbass]

I have a tiny 5mW red laser pointer that runs off of 3 LR41s. Should this work for me? What diode would anyone recommend getting?

[pbates123]

I'm confused.

You said "I believe given the same mW a violet laser will burn the best" Then you said "but a 40mW green is probably more powerful than a 5mW violet."

40 mW's or .040 watts will always be more power than 5mW's, .005 watts right?

Did you mean to say a 40mW violet is probably more powerful than a 50mW green laser or something similar?

Not being a laser person I would imagine there is more to the equation. Like regardless of the laser color it depends on how much of the energy the material absorbs. Isn't that why black which absorbs everything burns best?
elabz eluded to this below.

So irrespective of laser power different materials will yield different cutting results...

I liked your instructable keep up the good work.

[ivanjacob]

violet and red are better for burning stuff green is better for pointing :)

[saintneko]

It might have something to do with the wavelength/energy capacity of the photons themselves - shorter wavelength light (violet being the shortest of the visible spectrum) naturally is higher energy than longer wavelength light (green being in the middle). Might also have something to do with the amount of power required to excite the diode, IIRC some colors require more power input to achieve the same power output. Might also have to do with how well constructed your device is and what level of precision your components have been manufactured to (i.e. using cheap-ass caps might make your power differential irrelevant due to higher current fluctuations doing... whatever they might do).

But these are just guesses based on my knowledge of physics and half remembered reading. The wavelength/energy ratios I'm sure of (my job involves materials characterization based on xray photon wavelength and energy, which are inversely related). Green is about ~550nm, blue is ~440, violet is ~400 and ultraviolet is somewhere below that.

But someone with more specific knowledge, please feel free to give me the correcting I deserve. :)

[a480641]

yes, the wavelength is more important than the wattage.
I've not fact-checked this, but i believe the watts are the brightness and the wavelength is the color/danger/burn-ey-ness

[pbates123]

The wattage is the amount of energy used pure and simple and relates to the joules/second - energy used. Although there is more to it. The energy consumed does not necessarily equal 100 percent of the laser output power there are losses due to heat and conversion efficiencies from electrons to light.

Brightness is a relative term. And in general more power in will result in more power out, that leaves out the fact that for the same amount of power in with different efficiencies you will have greater or lesser intensity of light (brightness?) out.

Please correct me if I am wrong I am just ranting out loud here.

Isn't it true that higher frequencies require more power to generate? If so it would appear to me to be that wattage in would not be a good measurement of the useable energy out of a laser.

Would it be better to measure the laser in candelas similar to the output of a light bulb or maybe something like BTU's and actual measurement of what it takes to accomplish the work???

Guess I need to dig out some physics books - careful smoke is coming out of my ears!!! OMG!!

[saintneko]

Wavelength is definitely the color.

I was looking around, and at least the high-end manufacturers rate their lasers in output wattage (which I'm guessing is the heat produced by the laser at X distance from the source).

Of course, the output power's ability to light something on fire is going to depend on the area it's concentrated in, that whole inverse square law of radiation being a total wet blanket.

I still wanna try this, because it would make a wicked 'cigarette' lighter.

[elabz]

As far as the source of lens, people often get high(er) power laser diodes from DVD-RW drives (my personal favorite source :) ) and there's plenty of lens in there. So, you get both the laser diode and the lens from the same drive.

I had to put together a housing for an odd-shaped laser diode some time ago (the attached image) and had some pictures taken to illustrate where the lens are located. See the post about DIY laser diode housing here . It describes the process based on a different set of parts (literally, hardware store, plumbing section) but the lens may still be useful in a hand-held build like yours.

As far as the burning ability of the diode, it greatly depends on the color of the material. Until you get into 1W+ ranges, there's no way it'll burn anything that has the same or similar color as the laser beam - it just reflects too well. Black is always the best. And I would say that you can start doing some useful burning (such as CNC foam cutting and engraving) at about 150mW or more. Pretty much the power of the diode from a DVD-RW drive, again.

Keep the great instructables coming!

Cheers!

[rockerape]

Where can we find the convex lens?

[ivanjacob]

nice!

[rimar2000]

Very interesting, thanks for sharing.

[ilpug]

I need to do this.

[merlinjim]

FYI, for laser lenses, plastic is higher quality. Glass lens typically degrade the beam quality more, have more internal reflections, and greater aspherism. Plastic lenses can be manufactured to be aspherical more easily and don't require specialized coatings to deal with laser light efficiently.

[Jor2daje]

Interesting, thanks for letting me know ill change the instructable.