An excimer laser is a type of ultraviolet laser that works by breaking molecular bonds rather than burning or cutting. The name “excimer” is short for “excited dimer,” referring to the short-lived molecules formed when noble gases (like argon or krypton) combine with reactive gases (like fluorine or chlorine) inside the laser chamber. Different gas combinations produce different ultraviolet wavelengths, and each wavelength suits a specific purpose. The most widely known applications are vision correction surgery and skin disease treatment, but excimer lasers also play a critical role in manufacturing the microchips inside your phone and computer.
How an Excimer Laser Works
What makes an excimer laser unusual is how it removes material. Rather than heating tissue or metal the way most people imagine a laser working, it operates through a process called photoablation. Each photon the laser emits carries enough energy (6.4 electron volts at the 193 nm wavelength used in eye surgery) to directly snap the chemical bonds holding molecules together. Those broken molecular fragments then fly off the surface at supersonic speeds, carrying excess energy away with them in the ejected plume.
Because the energy is absorbed almost entirely at the surface, penetrating only about 0.3 micrometers deep per pulse, the tissue or material underneath stays largely unaffected. There is minimal heat transfer to surrounding areas. This is why excimer lasers are sometimes called “cold lasers.” The combination of precision and minimal collateral damage is what makes them so valuable in medicine and manufacturing alike.
Vision Correction: LASIK and PRK
The best-known use of excimer lasers is reshaping the cornea to correct vision. The 193 nm wavelength is ideal for this because the proteins and other molecules in the cornea absorb it almost completely. The laser doesn’t cut like a scalpel. Instead, it vaporizes microscopic layers of corneal tissue with each pulse, sculpting the cornea into a new shape that bends light more accurately onto the retina.
In LASIK, a thin flap is first created on the cornea’s surface (typically using a separate femtosecond laser), then lifted so the excimer laser can reshape the tissue underneath. In PRK, the outer layer of the cornea is removed entirely before the excimer laser does its work, and that outer layer regrows naturally over several days. Both procedures use the same fundamental reshaping principle, just with different preparation steps.
How the laser corrects different vision problems comes down to where pulses are concentrated. For nearsightedness (myopia), the laser delivers more pulses to the center of the cornea, flattening its curvature. For farsightedness (hyperopia), pulses are concentrated around the edges, steepening the curve. Astigmatism is corrected by selectively removing tissue along the steepest part of the cornea to make its shape more uniform, effectively treating irregularities up to about 4 diopters.
Modern excimer laser systems have become increasingly sophisticated. Wavefront-guided platforms map the unique imperfections in each eye and customize the laser pattern accordingly, producing better visual acuity and quality of vision than earlier one-size-fits-all approaches. Topography-guided treatments are another option, particularly useful for eyes with highly irregular corneas. Several FDA-cleared systems are currently in use, including the WaveLight EX500 from Alcon, the Carl Zeiss MEL90, and the STAR system from AMO Manufacturing.
How Excimer and Femtosecond Lasers Differ
People often confuse these two because both are used in the same procedure. They do completely different jobs. The femtosecond laser operates at an infrared wavelength and creates precise cuts, like the corneal flap in LASIK. The excimer laser operates in ultraviolet and reshapes tissue by vaporizing it. In LASIK, the femtosecond laser opens the door; the excimer laser does the corrective work. A newer procedure called SMILE uses only a femtosecond laser to extract a small lens-shaped piece of corneal tissue, skipping the excimer laser entirely. Studies show SMILE achieves similar safety and effectiveness to LASIK while preserving more corneal nerve fibers and structural strength.
Treating Skin Conditions
A different type of excimer laser, operating at 308 nm rather than 193 nm, is used in dermatology to treat conditions like psoriasis and vitiligo. This wavelength delivers concentrated ultraviolet B (UVB) light to affected skin patches without exposing the surrounding healthy skin, which is a significant advantage over traditional full-body light therapy.
For psoriasis, results can appear quickly. Noticeable clearing of plaques has been observed even after the first session, and improvements tend to persist even as treatment frequency tapers off. Combining the excimer laser with topical treatments like calcipotriol or dithranol produces better results than the laser alone.
For vitiligo, the laser stimulates repigmentation in the affected white patches. Success depends heavily on location: the face and neck respond best and tend to repigment more quickly, while joints and extremities are the most resistant to treatment. Combining excimer laser sessions with topical tacrolimus (a cream that modulates the local immune response) outperforms laser treatment on its own. How long a person has had vitiligo also matters, with newer patches generally responding faster.
Clearing Blocked Arteries
Excimer lasers also have a role in cardiology. A procedure called excimer laser coronary atherectomy (ELCA) uses a tiny catheter threaded into blocked arteries to break apart hardened plaque, including heavy calcification that other tools struggle with. The catheter delivers 308 nm pulsed ultraviolet light, and its shallow penetration depth reduces the risk of puncturing or tearing the vessel wall.
The laser works through three simultaneous effects: photochemical (breaking molecular bonds), photothermal (controlled heat), and photomechanical (pressure waves). The resulting debris particles are mostly smaller than 10 micrometers, small enough to be filtered out naturally by the body’s waste-clearing systems, which keeps the risk of downstream blockage very low. ELCA is typically reserved for complex cases, including blockages inside previously placed stents, heavily calcified lesions, blockages at vessel branch points, and clot-heavy deposits where mechanical drilling tools may not be the best option.
Semiconductor Manufacturing
Outside of medicine, excimer lasers are essential to the production of computer chips. In photolithography, the process used to etch microscopic circuit patterns onto silicon wafers, a high-powered excimer laser shines ultraviolet light through a patterned mask onto a light-sensitive coating on the wafer. Wherever the light hits, it changes the coating’s chemistry so it can be washed away, leaving behind the circuit pattern.
The short wavelength of excimer laser light is what makes this possible. Shorter wavelengths can create finer details, and with advanced optical techniques, chipmakers can now produce features far smaller than the laser’s own wavelength. The high power output of excimer lasers also keeps production lines running at the speeds needed to manufacture chips in commercially viable quantities. Nearly every modern processor, memory chip, and smartphone component has been shaped, at some stage, by an excimer laser.