The history of the excimer laser

The excimer laser's history began in the 1970s with the theoretical understanding of excited dimers (excimers) and their potential for lasing. Early experiments using rare gas halides like ArF and KrF demonstrated the feasibility of this technology, leading to the development of increasingly powerful and efficient excimer lasers throughout the 1980s and 90s. These lasers, utilizing ultraviolet light, found rapid applications in microelectronics, laser surgery (particularly in ophthalmology and dermatology), and materials processing, driven by their unique properties of high power and short wavelength. Continued research and development led to improved efficiency and stability, solidifying the excimer laser's place as a key technology in various fields.

The history of the excimer laser is a story of scientific curiosity leading to a powerful technology with widespread applications. Its development wasn't a single "eureka" moment but rather a gradual process built upon advancements in several fields.

Early Days & Theoretical Foundations (1930s - 1970s):

• The theoretical groundwork was laid much earlier than the actual laser development. Understanding the excited states of diatomic molecules, particularly the formation of excimers (excited dimers), was crucial. This understanding grew throughout the mid-20th century through advancements in quantum mechanics and spectroscopy.
• Early experiments with discharge lamps produced excited dimer species, but didn't achieve lasing. The challenge lay in efficiently creating a population inversion (more molecules in the excited state than the ground state), a necessary condition for stimulated emission – the heart of laser operation.

The Breakthrough (1970s):

• The crucial breakthrough came in the early 1970s, independently by several research groups. Researchers found ways to effectively create and sustain a population inversion in excimer molecules. This involved using electrical discharges or electron beams to excite a mixture of a rare gas (like Argon or Krypton) and a halogen gas (like Fluorine or Chlorine).
• The first successful excimer laser was a KrF excimer laser, demonstrated around 1975. This achievement confirmed the feasibility of using excimers for laser operation. Other excimer laser types (XeCl, ArF, XeF) quickly followed.

Development and Refinement (1980s - Present):

• The 1980s saw significant improvements in excimer laser technology. This included advancements in gas handling, better discharge techniques, and the development of more robust and efficient laser designs.
• Applications rapidly expanded. The excimer laser's unique ultraviolet (UV) wavelength proved particularly valuable in several areas.

Key Applications:

• Microlithography (semiconductor industry): Excimer lasers, particularly KrF and ArF, revolutionized microchip fabrication by enabling the creation of ever-smaller features on integrated circuits. This was crucial for Moore's Law's continued advancement.
• Laser eye surgery (LASIK): Excimer lasers became a cornerstone of refractive surgery, precisely reshaping the cornea to correct vision problems.
• Medical applications: Beyond LASIK, excimer lasers found use in dermatology (treating skin conditions like psoriasis), cardiovascular surgery, and other areas.
• Materials processing: Their high-energy UV output allowed for precise etching and ablation of various materials.

Current Status:

While newer laser technologies are emerging, excimer lasers remain important in certain niche applications. Their high power output and specific UV wavelengths continue to make them valuable tools, especially in microfabrication. However, their use in some areas like LASIK is gradually being replaced by newer, potentially safer techniques. The history of the excimer laser is a testament to the power of fundamental scientific research leading to transformative technological applications.