The short answer: LASIK uses ultraviolet light at a wavelength of 193 nanometres, produced by an argon-fluoride (ArF) excimer laser. That single number — 193 nm — is responsible for the entire procedure working. It sits at a very specific point on the electromagnetic spectrum where photon energy is high enough to break molecular bonds in corneal tissue without causing thermal damage to the surrounding cornea. No shorter, no longer, no different wavelength has matched its clinical profile for corneal reshaping in more than three decades of use.
If you have ever wondered what actually happens when the laser passes over your eye during LASIK — why it makes that faint burnt-smell, why the tissue disappears cleanly without heating up, why the whole thing takes less than a minute per eye — the answer lives in the physics of this one wavelength. This guide from Visual Aids Centre walks through what electromagnetic radiation is, why UV at 193 nm specifically was chosen for eye surgery, what an excimer laser actually does, and where the technology may be heading next.
Key Takeaways
- LASIK uses ultraviolet light at 193 nanometres from an argon-fluoride (ArF) excimer laser.
- 193 nm breaks molecular bonds in corneal tissue without generating significant heat — the core advantage over other wavelengths.
- The process is called photoablation: each pulse removes a precisely controlled layer of tissue, roughly 0.25 microns deep.
- Femtosecond lasers, which create the LASIK flap, use near-infrared light at 1053 nm — different job, different wavelength.
A Quick Word on the Electromagnetic Spectrum
The electromagnetic spectrum is the full range of electromagnetic radiation — radio waves at one end, gamma rays at the other. In between sit microwaves, infrared light, visible light, ultraviolet, and X-rays, ordered by decreasing wavelength and increasing photon energy. Visible light, the slice your eyes can perceive, spans roughly 380 to 750 nanometres. Ultraviolet radiation is shorter and more energetic, from about 100 to 380 nm, subdivided into UVA, UVB, UVC, and deeper regions.
LASIK operates in what physicists call the deep ultraviolet (DUV) region. At these short wavelengths, each photon carries enough energy to rupture specific chemical bonds in soft tissue — a property that turns out to be ideal for the exact medical task of reshaping the cornea one sub-micron layer at a time. For the broader context of the procedure itself, our article on what happens in laser eye surgery covers the step-by-step process at a clinical level.
Why 193 Nanometres Specifically
Excimer lasers can produce several different wavelengths depending on the gas mixture used — 193 nm (ArF), 222 nm (KrCl), 248 nm (KrF), 308 nm (XeCl), and 351 nm (XeF). Of these, 193 nm turned out to be uniquely suited for corneal refractive surgery for three compounding reasons.
First, at 193 nm the photon energy — roughly 6.4 electronvolts — is high enough to break the carbon-carbon and carbon-nitrogen bonds in corneal collagen directly, without relying on heat. This is critical. Thermal ablation would cook surrounding tissue, produce uneven results, and trigger an inflammatory response. Photoablation at 193 nm evaporates tissue cleanly in a process that happens too fast for heat to spread.
Second, water absorbs 193 nm UV extremely efficiently — within roughly one micron of tissue depth. This means the energy delivered by each pulse is consumed in a very shallow layer, giving surgeons precision at the scale of 0.25 microns per pulse. The cornea beneath that layer is essentially untouched.
Third, 193 nm photons are absorbed within the cornea so completely that almost nothing reaches the lens or retina. The anterior segment of the eye acts as a natural shield for the posterior structures, so retinal damage from LASIK treatment is not a realistic risk.
Longer UV wavelengths — 248 nm, 308 nm — either produce more thermal effect, penetrate too deeply, or damage DNA in ways that raised early safety concerns. The 193 nm wavelength sits in a rare sweet spot that the industry has not found reason to leave. For a deeper look at the laser-planning technology built around this wavelength, see our article on how ray tracing technology creates precise ablation profiles.
What an Excimer Laser Actually Is
“Excimer” is short for “excited dimer” — a reference to the short-lived molecule that exists only in the laser’s active medium. In an ArF excimer laser, argon atoms and fluorine atoms are electrically excited to form an ArF* dimer (the asterisk denoting the excited state). This dimer is unstable; within a few nanoseconds it dissociates back into separate argon and fluorine atoms, releasing a photon at exactly 193 nm in the process. Millions of these transitions, triggered in a coordinated pulse, produce the characteristic ultraviolet laser beam.
The laser delivers its energy in pulses, not a continuous beam. Each pulse lasts only a few nanoseconds and carries a small, precisely calibrated amount of energy. A modern LASIK treatment uses a few hundred to a few thousand pulses per eye, with the laser system computing in real time how much tissue each pulse should remove and where. Our article on the history of LASIK eye surgery covers how this technology evolved from laboratory experiments in the 1980s to the routine clinical tool it is today.
Photoablation — How the Laser Reshapes the Cornea
When a 193 nm photon hits a molecule in the corneal stroma, it transfers enough energy to break that molecule’s covalent bonds. Bonds breaking in large numbers, simultaneously, within a thin layer, produce a micro-explosion that ejects the affected tissue as a plume of dissociated molecular fragments. That plume carries away the heat with it, leaving the underlying cornea at close to body temperature.
This is photoablation — removal of tissue through photochemistry rather than heat. Surgeons calibrate each patient’s treatment based on their corneal topography map, refractive error, and corneal thickness. The laser then fires the calculated pattern of pulses, sculpting the cornea to a new, optically corrected curvature. The full LASIK procedure combines this ablation step with the flap-making step that precedes it. And for patients curious about whether the procedure affects the deeper layers of the cornea, our article on whether LASIK destroys Bowman’s layer addresses that specific anatomical question.
The Other Laser in LASIK — Femtosecond
Modern LASIK actually involves two different lasers operating at two entirely different wavelengths. The excimer at 193 nm does the reshaping. A femtosecond laser, typically operating in the near-infrared at around 1053 nm, does the flap-making step that precedes the reshaping. The femtosecond laser works not by breaking bonds but by creating tightly focused plasma micro-bubbles in the corneal tissue, which together form a clean dissection plane.
This dual-laser approach replaced the old mechanical microkeratome blade and is what differentiates today’s procedure from its earlier forms.
Where the Technology Is Heading
Research groups have explored whether shorter excimer wavelengths — particularly krypton chloride at 222 nm — could improve on the 193 nm standard. Early studies suggest 222 nm may offer certain technical and safety advantages, including gentler exposure profiles and potentially different interaction with ocular tissue. To date, though, no 222 nm system has displaced 193 nm in mainstream refractive surgery; the established wavelength continues to dominate clinical practice because the decades of outcome data behind it are hard to match without compelling reasons to switch.
The broader trajectory of refractive surgery is moving less toward different wavelengths and more toward smarter treatment planning — AI-assisted calculations, topography-guided customisation, real-time tracking — all using the same underlying 193 nm ArF excimer beam. The physics of the wavelength has aged remarkably well.
Conclusion
The short electromagnetic answer is 193 nanometres, produced by an argon-fluoride excimer laser — a specific slice of deep ultraviolet light whose combination of photon energy, tissue absorption, and near-zero thermal spread makes it uniquely suited to reshaping the cornea. Combined with a femtosecond laser at 1053 nm for flap creation, this is the electromagnetic toolkit behind every modern LASIK procedure performed worldwide. If you are considering LASIK and want to see the technology in person or understand how it applies to your specific refractive error, book a consultation at Visual Aids Centre.
Frequently Asked Questions (FAQs)
What type of laser is used in LASIK surgery?
An argon-fluoride (ArF) excimer laser, which produces ultraviolet light at 193 nanometres. Modern LASIK also uses a femtosecond laser at around 1053 nm for flap creation.
Why is 193 nm used rather than other UV wavelengths?
At 193 nm, photon energy is high enough to break corneal molecular bonds without generating heat. Water absorbs it in roughly one micron, giving extreme precision, and the photons don’t reach the retina.
Is the laser in LASIK harmful to the eye?
No. The 193 nm beam is fully absorbed in the top microns of the cornea and doesn’t reach deeper structures. Photoablation works without thermal damage or DNA disruption in surrounding tissue.
Is LASIK the same as laser eye surgery?
LASIK is one type of laser eye surgery. Others include SMILE, PRK, and Trans-PRK. See is laser and LASIK the same for the full comparison.
How deep does the LASIK laser go into the cornea?
Each pulse removes approximately 0.25 microns of tissue. Total depth depends on the correction required but rarely exceeds 100 microns — far less than the full corneal thickness of around 500 microns.
Why does LASIK sometimes produce a slight burning smell?
The smell is the plume of dissociated tissue molecules ejected during photoablation. It’s harmless and dissipates within seconds in a well-ventilated theatre.
