What is an excimer laser?
Release time:
2025-10-21
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Excimer lasers are a class of gas lasers that operate based on the stimulated emission transition mechanism involving excimer molecules—transient compounds formed when inert gases combine with halogen gases in an excited state (e.g., ArF, KrF, XeCl). These lasers emit light at wavelengths in the ultraviolet range (157–353 nm) and are characterized by high photon energy, large peak power, and narrow pulse widths (typically tens of nanoseconds). They currently represent an important source of high-power coherent radiation in the deep ultraviolet region.
From the perspective of energy-level structure, excimer lasers belong to a four-level system. Excited-state molecules (E₁) can emit laser radiation when they transition to the repulsive or weakly bound ground state (E₀); meanwhile, the ground-state molecules rapidly dissociate, naturally leading to population inversion and reducing the laser oscillation threshold. This characteristic enables these lasers to achieve efficient energy output even when the output coupler has a relatively low reflectivity (10%–30%).
In terms of engineering implementation, typical excimer lasers use high-voltage pulsed discharge to excite the working gas. The typical gas mixture composition consists of 2%–9% inert gas, about 0.2% halogen gas, and the remainder being buffer gases (such as neon). The operating pressure is maintained within the range of 3.5–5.0 atm. As the number of pulses accumulates, the gas gradually depletes due to chemical reactions and adsorption, leading to a decline in laser performance. Therefore, industrial systems are equipped with periodic gas-replenishment mechanisms. In recent years, through optimization of electrode materials—such as the use of nickel or bromine-compatible materials—and improvements in the inorganicization of sealing and insulating components, the gas lifetime has been significantly extended to the order of 10⁸ pulses, while system stability and safety have also been enhanced.
Although excimer lasers have certain limitations in terms of beam quality—such as multimode characteristics and relatively large divergence angles—as well as system integration, they still occupy an irreplaceable position in lithography, medicine, spectroscopic detection, and scientific research thanks to their outstanding power performance in the ultraviolet wavelength range. In particular, in the field of semiconductor lithography, KrF (248 nm) and ArF (193 nm) lasers, as the mainstream deep-ultraviolet light sources, continue to support the development of nanoscale integrated circuit manufacturing processes. Moreover, in scientific research instruments, excimer lasers are often used as pump sources for dye lasers or to generate high-order harmonics, and they find wide applications in areas such as atmospheric remote sensing, laser spectroscopy, and precision measurement.
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