Defocused Laser Applications



@dan has mentioned this is a feature planned for the future on occasion. And a few applications have been mentioned here and there. I am curious what other ideas people have, and want it all in one location for future reference when the feature exists.

First off, what does defocusing mean?
–There is a lens which puts all the power of the laser in one tiny spot. That is why a 45W laser, which is delivering the same power into the world as a 45W light bulb, can cut materials. Because instead of general power to everywhere around it, this is power highly focused in one tiny area. When you de-focus, that means you are moving away from that focal point, to somewhere that the power is more spread out. So you no longer can get as high of a power at one specific point, instead it is spread across an area.

Previously mentioned:

  1. Cooking Food (I think specifically Bacon was mentioned)
  2. Heating Acrylic (you would do this so you can fold it, but this requires a larger void inside the laser cutter so you can flip over what you are working on)

Random ideas I have had which spurred making this thread in the first place:

  1. Finishing 3D prints. With ABS you can use boiling Acetone to vapor smooth a print, this makes it glossy and awesome, nobody can tell it is 3D printed (or at least it is much harder to see it was). There are some people who have listed chemicals that should do the same with PLA, but I haven’t thus far tried it. But… with a defocused laser, you could heat the plastic up and achieve the same results.
  2. Charring - After making a cut, or in lieu of one, you can char the material to get different colors. In fact, with the laser being able to adjust power settings and focal plane on the fly… you should be able to char with calligraphy level of brushstroke variation.
  3. Larger Kerf - Defocusing means less power per spot of material. But if your material only needed 10% power to cut anyway, then being defocused to a fair extend still cuts the material. So with easier to cut materials, you can have different line thickness cuts (again… calligraphy applications, and other I am sure)
  4. Hemispherical divots - Essentially a copy of the third idea here. But without moving around. Keep the laser in one spot, and draw the focal plane back, while delivering enough power to burn away a layer of material. This will engrave the center deepest, and less total material loss as you move out from that point. This may be an extreme fire risk though.
  5. Plastic Welding - You could apply iron on stickers, or you could seal the edges around a custom shaped balloon.

Defocusing the Laser: HOW will it be controlled?
Laser settings
Laser Welding of Acrylic
Any testing or input yet on bending acrylic?
Using a laser cutter with thermoform paper

Another thread linked to to chamfer the edges on at least the top of acryllic.

and mentions doign it to get a thicker line. So #3 is a solid thing


This is awesome. Holy cats I can’t wait to see what you all do with this.


Sounds like a good way to age/weather stuff.
I always wanted to make a very old looking treasure map that has been through wars and such.
Maybe on hide or a good old timey made paper. Good way to discolor parts without burning and all that.


OK I just had the best idea ever for a defocused laser. Make a bunch of (short) creme brulees and then do a design in the caramelized sugar :smile:

Alternately you could just make a bunch of sugar circles (on a silicone mat or something) the size of the inside diameter of your ramekins and just put them on top but that may be considered cheating :slight_smile:


First thing I thought of was I could defrost my meat a lot faster this way :smiley:


Great, now I am thinking of food too. Bake your own chips or fries would be fun to try. Perfectly cut fries to boot.
Melt marshmallows and chocolate for the perfect smore maybe too.


The food applications are pretty limited, since this would be strictly surface heating. So caramelizing sugar to make designs, searing the surface of meats, or cutting thin foods (noodles maybe, seaweed obviously, rice paper, wonton wraps…).

I could be way off, since I have no experience to draw on. But the food applications ought to be rather minimal.


@dan - you going to have a pre-set graham cracker setting? For engraving on our smores?


Feature bucket ahoy!


I really want to try cutting fondant or gumpaste. Or maybe engrave? Dan mentioned freezing chocolate (Wilton Candy Melt?) before… In theory I think if the fondant or gumpaste have dried/freezed it could work. Maybe wafer paper or icing sheet too?


Oh my ! … I just spent $3500 on a device that all I can think about now is monogramming marshmallows !!!


customized “conversation hearts” candy messages?


I know you are a physics professor and probably feel the need to speak to all levels background here, but doesn’t the A in LASER stand for amplification?
It has always been my understanding that besides being monochromatic and coherent, a laser actually throws more photons than a non-lased source of the same power input ever could, due to stimulated emission. Is my understanding wrong or incomplete?
Yes, I understand that there is no free lunch, I’m just talking about efficiency.
Even at my age I am always eager to learn.



There are tons of mass over simplifications any time you step into common speech. The watt rating on a lightbulb is power consumption, which for an old style bulb was mostly spent on heat. So making a comparison in terms of photon delivery to a bulb through wattage is wrong on many levels. But it is still a fairly useful analogy at a very low level of discussion.

The amplification term in LASER is a misnomer for most lasers we know of today. I don’t know that initial models of the laser system were actually provided with input light, but the idea was that you put a constant light beam in, and then you get pulsed light out which is higher intensity in each pulse than the input beam was.


I usually refer to the heat of a 40w light bulb, which is in fact 40w of heat. You’re right that only about 4w comes out as visible light (which gets absorbed and produces heat) and 36w comes out as “heat” directly… mostly via IR, like a laser. So I think it’s a pretty good analogy.

As far as the acronym, if memory serves:

  • Every laser is energized by something. Some lasers are pumped via light sources, for example early ruby lasers or some modern fiber lasers. The goal is that the lasing medium (in our case a gas mix containing CO2) gets excited, and has lots of high energy electrons.
  • The amplification bit is that the lasing medium is put in an unstable state where the electrons are high-energy and want to drop down a level, releasing a photon. When an inbound photon hits it, the 2 photons coming out are more likely to be the same phase and direction as the inbound photon. So one input photon stimulates two outbound photos, effectively amplifying it. This is fundamental to lasing, and happens even in CO2 lasers that are energized with electricity instead of pumped with light.

Someone correct me if I’m wrong here.


That is the way I understand it. As usual, Wikipedia had a pretty good primer.


I’ll be looking to defocus so I can cut closed-cell foam (assuming material doesn’t make chlorine gas, which I don’t think it does) without the kerf issues or resealing.


One of the things I am looking at making with my Glowforge when I get it is a Fresnel lens. The first step would be to take acrylic and engrave it with a raster image to get the curves. Next would be to have an defocused pass to smooth everything out. So I am very much interested in this topic.

How precise is the Glowforge?

Whoa, that’s a really cool idea! Making totally custom fresnel lenses would be absolutely amazing.

(definitely not for making death rays)