An excimer laser is a type of ultraviolet laser that uses a mixture of noble gas and halogen gas to produce powerful, precisely targeted pulses of light. The name comes from “excited dimer,” referring to the short-lived molecules that form inside the laser and release energy as ultraviolet photons. These lasers are best known for reshaping the cornea during LASIK eye surgery, but they also treat skin conditions like psoriasis and play a critical role in manufacturing computer chips.
How an Excimer Laser Works
Inside the laser chamber, a noble gas like argon, krypton, or xenon is mixed with a halogen gas like fluorine or chlorine. An electrical discharge ionizes the noble gas atoms, and those ionized atoms bond with the halogen atoms to form unstable molecules called excimer complexes. These molecules exist only in an excited energy state. When they drop back down and fall apart into their separate elements, they release that energy as a pulse of ultraviolet light.
The specific gas combination determines the wavelength of light the laser produces. The four most common types are argon fluoride (193 nm), krypton fluoride (248 nm), xenon chloride (308 nm), and xenon fluoride (351 nm). Swapping out the gas mixture in a commercial excimer laser changes its output wavelength, making these systems versatile across different applications.
What makes excimer lasers distinctive is how they interact with materials. The ultraviolet photons carry enough energy to directly break chemical bonds in whatever they hit. Instead of heating and melting a surface, the laser essentially vaporizes material bond by bond, a process called photoablation. The target material goes straight from solid to vapor with no liquid phase in between, and surrounding tissue or material stays cool and undamaged. This cold, precise removal is what makes excimer lasers so valuable in medicine and manufacturing.
Excimer Lasers in Eye Surgery
The connection between excimer lasers and eye surgery dates to 1983, when ophthalmologist Stephen Trokel collaborated with researchers at IBM’s Thomas J. Watson Research Center. Samuel Blum, Rangaswamy Srinivasan, and James Wynne had been exploring new uses for excimer lasers, and Trokel recognized the potential for reshaping the cornea. Their landmark paper, published that December, launched a global research effort that eventually produced modern refractive surgery.
In LASIK and PRK, the 193 nm argon fluoride laser reshapes the cornea by removing microscopic layers of tissue through photoablation. Because the ultraviolet energy breaks molecular bonds without generating heat, the surrounding corneal tissue remains intact. This precision allows surgeons to correct nearsightedness, farsightedness, and astigmatism by sculpting the cornea into a shape that focuses light correctly onto the retina.
The excimer laser handles one specific step in LASIK: the actual reshaping. A separate tool, often a femtosecond laser, creates the thin flap on the cornea’s surface beforehand. Femtosecond lasers use extremely short pulses of infrared light and are better suited for cutting tissue cleanly, while excimer lasers excel at controlled removal. In newer procedures like SMILE, femtosecond lasers handle the entire surgery without an excimer laser, achieving similar safety and effectiveness with greater preservation of corneal nerves and structural strength. Wavefront-guided technology has also improved excimer laser treatments, allowing surgeons to customize the reshaping pattern to each eye’s unique optical imperfections.
Treating Skin Conditions
The 308 nm xenon chloride excimer laser has become a well-established treatment for localized skin conditions, particularly psoriasis and vitiligo. Unlike traditional UV light therapy, which bathes large areas of skin in ultraviolet light, the excimer laser targets only the affected patches. This spares healthy surrounding skin from unnecessary UV exposure.
For localized psoriasis, the 308 nm excimer laser outperforms standard narrowband UVB therapy. It clears plaques in fewer treatment sessions with a lower total UV dose. A typical course involves twice-weekly sessions for up to 24 treatments, with the energy level adjusted based on how your skin responds. If there’s no redness after a session, the dose goes up by 25%. If significant redness or blistering occurs, it comes down. Research suggests the laser works partly by modulating the immune response in treated skin, nudging it toward a more balanced state.
Side effects are generally mild and consistent with what you’d expect from any UV-based therapy: redness, occasional blistering, and changes in skin pigmentation. Darkening of the treated area is the most common reaction, especially in children. These effects are typically temporary. One limitation is that excimer laser devices are large and restricted to clinical settings, so home treatment isn’t an option.
Role in Semiconductor Manufacturing
Excimer lasers are essential to photolithography, the process used to etch the incredibly small circuit patterns onto computer chips. The shorter the laser’s wavelength, the finer the details it can print. The 193 nm argon fluoride laser has been the industry workhorse for producing the tiny features on modern processors and memory chips. Krypton fluoride lasers at 248 nm served this role in earlier chip generations.
In manufacturing, the laser’s ability to ablate material precisely at atmospheric pressure opens up possibilities beyond traditional vacuum-based processes. Pattern transfer through laser ablation involves the laser photons being absorbed by the material, which is then removed in a controlled fashion. The ablation rate of the masking material versus the substrate determines how deep and how cleanly patterns can be transferred, and parameters like the angle of the laser beam can be adjusted to fine-tune the results.
How Excimer Lasers Compare to Other Lasers
Most lasers people encounter, from laser pointers to those used in cosmetic procedures, operate in the visible or infrared spectrum and work primarily through heat. They warm, melt, or burn their targets. Excimer lasers operate in the ultraviolet range and remove material through direct bond-breaking rather than thermal damage. This fundamental difference is why excimer lasers can reshape a cornea without cooking the tissue next to it, or etch nanometer-scale chip features without melting adjacent structures.
Excimer lasers are also pulsed rather than continuous. Each pulse delivers a brief, intense burst of energy, and the amount of material removed scales predictably with the number of pulses. This gives operators extremely fine control. In eye surgery, for example, each pulse removes a fraction of a micrometer of corneal tissue, allowing the surgeon to sculpt corrections measured in millionths of a meter.
The tradeoff is complexity. Excimer lasers require pressurized toxic gases, high-voltage electrical systems, and regular gas refills. They’re large, expensive, and need specialized maintenance. You won’t find one outside of a hospital, research lab, or semiconductor fabrication plant. But for applications demanding cold, precise material removal at ultraviolet wavelengths, nothing else does the job quite the same way.