Lesson 13.6Micro & nanoChapter 13 · Micro- and nanofabrication

Femtosecond laser machining

Removes material with ultrashort laser pulses, without melting

Femtosecond laser machining cuts, drills and textures material with laser flashes lasting less than a trillionth of a second. Each flash vaporizes a thin layer before heat can spread, so edges come out clean instead of melted. Makers of heart stents, phone cover glass and fuel injectors use it where even slight heat damage matters.

Photo: paul_houle, CC BY-SA 2.0, via Wikimedia Commons

femtosecond laser machining · the machine and a zoom on the spotCircled numbers match the steps below; the two framed panels zoom in on the spot where light meets material.

How it works

Make ultrashort pulses. An oscillator (the laser's pulse-making core) emits a steady train of weak pulses. Each lasts tens to hundreds of femtoseconds (a femtosecond is a millionth of a billionth of a second).
Amplify them. An amplifier stretches each pulse, boosts its energy, then squeezes it short again. This trick, chirped pulse amplification, won the 2018 Nobel Prize in Physics.
Aim and focus. A scanner (two fast-turning mirrors) steers the beam. A lens focuses it to a spot a few microns wide (a micron, or µm, is a thousandth of a millimeter).
Cold ablation. The pulse dumps its energy faster than atoms can pass heat to their neighbors. A thin layer is ablated, meaning blasted off as vapor and plasma (hot, charged gas), with almost no melting.
Scan the path. Hundreds of thousands of pulses per second or more trace the programmed path, layer by layer, to cut, drill or texture. Focused inside clear glass, the pulses can even write channels without touching the surface.

Key facts

Materials: Almost anything: steel, titanium, nitinol (a shape-memory alloy), glass, sapphire, ceramics, polymers, even eye tissue
Typical parts: Heart stents, micro-holes in fuel injectors and circuit boards, cutouts in phone cover glass, textured surfaces
Part size: Features from about 1 µm to millimeters; parts usually small or thin (tubes, sheets, foils)
Precision: Typically a few microns; features down to about 1 µm
Surface finish: Clean, burr-free edges with almost no heat-affected zone (the band of material altered by heat)
Batch size it suits: Prototypes to large series of high-value parts (stents, phone glass, battery foils)
Tooling and machine cost: No tooling; a laser workstation typically costs several hundred thousand dollars
Speed: Hundreds of thousands of pulses per second, yet slow bulk removal: typically cubic millimeters per minute

Strengths and limits

Strengths

Almost no heat damage: no burrs, melted rims or cracks
Works on glass, sapphire, ceramics and heat-sensitive plastics
Micron-scale detail, with no tool contact and no tool wear
Can modify the inside of glass without touching its surface

Limits

Removes material slowly compared with conventional lasers
Laser sources are expensive and complex
Tuning pulse energy, rate and overlap is delicate
Suits small parts and thin sections; fumes need extraction

Where it's used

Medical devicesCoronary stents, catheters, micro-needles
Consumer electronicsPhone cover glass, sapphire camera covers, display cutouts
ElectronicsMicro-vias (tiny holes linking circuit-board layers), wafer dicing
BatteriesCutting and structuring electrode foils
Eye surgeryCorneal flaps for LASIK, steps of cataract surgery
Automotive and aerospaceFuel-injector holes, cooling holes, friction-reducing surface textures

How to recognize it

Usually you can't: the features are microns wide and end up hidden inside stents, phones, circuit boards and engines.
Cut edges on glass or metal that look perfectly clean, with no burn color, no burr and no beads of re-solidified metal.
Under a magnifier, crisp round micro-holes, often slightly tapered (wider on the side the laser entered).
Laser-textured metal that shimmers with rainbow colors: the pulses leave ripples fine enough to split light into colors.

Compare with

Laser cutting6.2a continuous or longer-pulsed beam melts and blows material away; far faster, but it leaves a heat-affected edge.Focused ion beam13.5removes material with a beam of ions (charged atoms) in a vacuum; finer, down to nanometers, but much slower.Two-photon polymerization13.8uses the same kind of laser to build rather than remove, hardening resin only at the focus.

Watch it

SME Media · A plain overview of what ultrashort pulses can do

CMS Laser · Cutting stent-like patterns from thin metal tubes

Spectra-Physics an MKS Brand · Close-ups of clean micro-cuts and holes

TRUMPFtube · Drilling circuit boards at production speed

See real photos

Wikipedia: Laser ablation — how pulsed lasers remove material; few photos
Wikipedia: Ultrashort pulse — what femtosecond pulses are and how they are made
Wikimedia Commons photo search

Remember

Pulses shorter than the time heat needs to spread remove material without melting it.
It machines almost any material, glass and tissue included, with micron detail.
The price is costly lasers and slow removal, so it suits small, high-value parts.