How Laser Engraving Works

So, to recap how laser engraving works: Laser hits material, material absorbs light from laser, that energy creates heat, enough heat that the material turns from a solid into a gas. When those layers have been vaporized away, you get a slightly indented area left behind in the shape of your design.

The reason you can see engravings so clearly is because the material in the lasered section will reflect light differently than the un-engraved material. And the laser’s narrow beam allows for incredible details – imagine drawing with a fine tip pen instead of a Sharpie.

How Lasers Work: The Short Version

The shortest possible explanation is that lasers work by concentrating a lot of identical (what physicists call “coherent”) light particles into a focused, high energy beam.

How Lasers Work: The Longer Version

The word “laser” is an acronym that helpfully explains how lasers work. It stands for:

• Light

• Amplification by

• Stimulated

• Emission of

• Radiation

Urgh, what?

Light amplification essentially means making very powerful light waves. You do that using stimulated emission: a way of forcing electrons to produce lots of identical (“coherent”) photons – particles of light. (Those particles of light are the radiation part of “laser”. ) When you have all these identical (coherent) photons together, they create a coherent light wave.

Typically in a laser, you put the light wave inside a cavity that has a mirror at each end. The light wave continuously bounces off each mirror, creating even more stimulated emission, and therefore more amplification. When you have enough amplification, the light beams escape through a slit in one mirror, and emerge as a highly focused laser beam.

Stimulated emission produces identical photons.

The photons form a wave.

The wave is reflected and amplified by mirrors.

The laser beam.

So instead of laser, they could have called it:

Making powerful light waves

By producing lots of identical particles of light

That act together as a focused beam

But MPLWBPLOIPOLTATAAFB is a mouthful.

Why is a coherent light wave so powerful? Imagine a showerhead and a hose under the same high water pressure. The water that sprays from the showerhead covers a wider area, but the force is spread across lots of streams, so it doesn’t feel as intense. In contrast, the water that comes out of the hose is concentrated into a single jet – now that’s gonna hurt. The showerhead spray is like how the light emitted from a lightbulb works, and the hose is like how light emitted from a laser works.

Unlike water, however, when laser light is absorbed by a material, all that energy generates heat – which is how (most) lasers cut or engrave: The heat melts, cuts, or vaporizes the material. Since different materials absorb light of different wavelengths, it’s really important to make sure you’re matching your particular type of laser with a material that will absorb it. Otherwise, you won’t get enough energy to create the heat.

This is also why reflective and clear materials are so pesky for some laser engravers. They reflect or refract light, which means some or all of the laser beam isn’t absorbed, and that means the laser can’t create the necessary heat.

Different Types of Laser Engraver

The fun thing about physicists is that they don’t quit. Which is why there isn’t just one type of laser, there are many. It’s also probably why we got to the Moon.

The reason you need different lasers is because you have different things you want to lase, and those things absorb different wavelengths. For example, metals absorb relatively low wavelengths, while plastics absorb higher wavelengths. The lower the wavelength, the higher the energy, and vice versa.

The four main lasers used to engrave things are diode lasers, carbon dioxide lasers, fiber lasers, and UV lasers. Suffice it to say that the fundamental difference between these laser types is that they create stimulated emission in different ways – which are sort of described by their names.

Diode Lasers

Diode lasers use a forward-biased semiconductor diode to produce stimulated emission. (The very short version is that it involves an electrical current.) You’ll find a low-power diode laser in the light toy you use to play with cats. But while that has a wavelength that comes out red, the more powerful diode lasers used to engrave have a wavelength that appears blue.

Diode lasers aren’t powerful enough to engrave metal, and they can’t engrave clear or transparent material because these interfere with the laser beam absorption. However, they do work on wood and can engrave the type of powdered coating often used on tumblers (technically this is laser etching) so they’re still useful for certain customization projects.

Carbon Dioxide Lasers

Yes, you guessed it, these ones use carbon dioxide! Plus some other gases. Carbon dioxide lasers produce infrared light at a wavelength that is absorbed particularly well by clear acrylics, plastics, ceramics, and organic materials (like paper or wood.) They still struggle with metal, but they’re the go-to laser for clear and transparent materials.

Fiber Lasers

Sadly fiber lasers are not made of fruit. The gain medium in a fiber laser is an optic fiber “doped” with a rare earth element (REE). REEs have specific properties that make them very reliable at stimulated emission. This type of laser uses glass cables to amplify and direct the light, instead of mirrors.

Fiber lasers emit wavelengths in the infrared light spectrum that are best suited to engraving metal – and they also engrave very fast compared to other types of laser. The advanced tech plus the increased power and efficiency also make them more expensive than other lasers: but they do also typically last longer, and are essential if you want to engrave metal.

UV Lasers

Unlike the other three laser engravers, UV lasers don’t use heat to remove layers. They have the lowest wavelength of all these lasers, which means their beams have the most energy – enough to cut the bonds that hold molecules together! It’s called cold marking, and you can use it on a wide range of materials, including glass, plastics, leather, crystal, and even food. However, it struggles with metals.

Materials You Can Engrave

As we’ve hinted already, it depends on the laser. Because different materials absorb certain wavelengths, you need a laser that produces the right wavelength for your material. Here’s what each laser is best at engraving:

Diode: Wood, powdered paint coating, dark-colored acrylic

Carbon dioxide: Plastics, wood, stone, ceramic, glass, paper

Fiber laser: Metal

UV laser: Wood, leather, glass, food, plastics, stone, ceramic, silicone

A note on plastics:

Some plastics produce toxic gases when lasered. (You need proper ventilation and protection no matter what you’re engraving, but some byproducts are acutely dangerous.) For example, ABS (used in pens, keychains, sunglasses, lots of other things) produces cyanide gas. Yes, that cyanide! Grim. PVCs and materials coated with resins release toxic, carcinogenic smoke when lasered, and polystyrene and polypropylene foams have a pesky habit of catching fire.

Meanwhile, some other plastics – including polycarbonate and HDPE – melt into a blobby mess under a non-UV laser instead of vaporizing, so you can’t see the design clearly. However, you can engrave a lot of other plastics, including acrylic, polyurethane, and PET.

A note on metals:

Some metals engrave better than others, and again, it comes down to wavelength, but also hardness: It takes more energy to engrave harder metals than softer metals. The most commonly engraved metals are aluminum, copper, steel, and gold. Stainless steel tends to be annealed rather than engraved, in order to maintain the chromium oxide layer that’s added to prevent rusting.

Laser Engraving vs Laser Ablation vs Laser Annealing

Laser engraving isn’t your only option for using a laser to make a mark on something. You also have laser ablation and laser annealing.

Laser Engraving

As we already know, laser engraving involves using a laser to remove layers of material by vaporizing it. It works best on thicker materials, because you’re cutting some away and you need enough left over that you’re not compromising the stability of the piece. Objects that engrave well include keychains, jewelry, and trophies and awards.

You might see laser engraving referred to as laser etching, but these are different. Instead of using a laser to vaporize the surface, laser etching melts the material – specifically metal. Etching looks less dramatic than engraving, but it’s also faster, requires less power (because it takes less heat to melt something than to vaporize it), and doesn’t remove layers, so it can work better on thinner pieces.

Laser Ablation

This is the same technique as laser engraving — using a laser to vaporize layers of material — but it’s usually used when removing a thin surface layer, rather than multiple layers. For example, if you wanted to add a design to a powder-coated metal tumbler, you could “ablate” the powder coat: vaporize the powder coat but leave the metal. This is a better option for engraving thin materials, since it doesn’t cause an indent.

Laser Annealing

In the other examples so far, the laser acts as a chisel or a blowtorch. In annealing (also called laser marking) the laser is more like a paintbrush. But a paintbrush that works by oxidizing metal below its surface, changing the color. This is pretty cool, because it means you can preserve the integrity of the surface.

Annealing works best on stainless steel, steel, and titanium. It’s often the preferred method for laser marking stainless steel, since unlike engraving and etching, it preserves the protective chromium oxide layer. And because annealing doesn’t create bumps or channels where viruses and bacteria can grow, it’s often used on medical devices and kitchen utensils.

How Different Types of Laser Marking Stand Up To Sandpaper

To find out which type of laser mark is the most durable, we used all three to add our logo to three steel blocks. We then sandpapered over the logos, taking a photo every five seconds. Here’s what happened after 30 seconds:

Engraved

The steel surface scratched to a shiny, polished finish, but the engraved area showed no damage at all. 10/10

Ablated

For this one, the block was coated with a layer of powdered paint, and the logo was ablated out of this coating. While the sandpaper didn’t wear away at the logo, it removed a lot of paint. 6/10

Annealed

Unlike the other two options, the sandpaper damaged the annealed logo as much as the block itself, making it look badly scratched up. 2/10

Laser Engraving Pros and Cons

Pros of Laser Engraving

• Lasers create long-lasting, detailed, and repeatable customizations on a wide range of materials – often at no extra cost when you’re ordering promotional items.

Cons of Laser Engraving

• Lasers are not toys (well, unless you’re a cat) and getting the most out of them safely requires training and experience. Also, you need the right laser for the job, otherwise you won’t get the clean finish you want.

The Bottom Line

Laser engraving is a quick and versatile way to add customized designs to a range of products. And unlike other methods, your design won’t fade over time. Essentially, cats are right, lasers are cool.