When we talk about the outstanding performance of 308nm excimer lasers in dermatological treatments—such as vitiligo and psoriasis—or in precision industrial processing, we often focus on their precise energy delivery and remarkable efficacy. But what exactly is the “heart” that powers this sophisticated device to emit that specific ultraviolet light?

The answer lies precisely in its core consumable—the specialized mixed gas.

The xenon chloride (XeCl) excimer laser is a continuous-pulse gas laser with a wavelength in the UVB range. Its pulse width typically ranges from about 10 to 30 nanoseconds. Clinically, laser emitters used for therapeutic purposes include the Xtrac (PhotoMedex, USA) [4–6], the Lambda Physics LPX105E [2, 3, 7, 8], and other types of emitters [9]. These devices often incorporate an XeCl gas system. The XeCl dimer consists of the inert gas xenon (with eight valence electrons in its outermost shell) and the halogen chlorine (with seven valence electrons in its outermost shell). When activated by an electric current, the dimer exists in a bound state and emits pulsed laser light. Parameters of different laser emitters may vary slightly. Taking the Xtrac AL7000 as an example, the laser it produces at 308 nm has a pulse width of 30 ns, a repetition rate of 154 Hz, and a single-pulse energy density of 2–3 mJ/cm². The laser beam is transmitted via a liquid-core optical fiber, enabling the generation of a square spot measuring 2 cm × 2 cm. During treatment, the spot size can be adjusted as needed, and an appropriate dose can be selected to achieve optimal therapeutic outcomes.

I. Why are mixed gases necessary? — The principle behind laser generation

The 308nm excimer laser gets its name from its working medium, the “excimer,” which refers specifically to unstable molecules that briefly bond in an excited state and rapidly dissociate back to their ground state.

For the 308 nm wavelength, the key excimer is XeCl (xenon chloride), which is formed when a xenon atom and a chlorine atom briefly combine under the excitation of a high-voltage electrical discharge. This “excited” XeCl* molecule is extremely unstable and quickly returns to its ground state, releasing a quantum of energy—in the form of a photon with a wavelength of 308 nanometers.

However, xenon and chlorine gases cannot directly and efficiently carry out this process on their own. This is where a third gas—typically neon, known as the buffer gas—comes into play. Thus, the working gas of a 308-nm excimer laser is essentially a “cocktail” composed of these three gases mixed together in precise proportions.

II. As a “consumable,” its lifespan is tied to replacement.

Why is this gas considered a “consumable”?

During the operation of the laser, each discharge consumes an extremely small amount of xenon and chlorine gas. More critically, the gas components undergo subtle physicochemical reactions with the electrodes and the inner walls of the cavity, leading to gas contamination and a shift in the gas composition ratio. This gradual “deterioration” process causes the laser’s output energy to decline steadily, its wavelength to become unstable, and ultimately renders it unable to meet the requirements of medical or industrial applications.

Therefore, just as a car requires regular refueling and maintenance, the 308nm excimer laser also needs periodic replacement of its gas cylinders (or “gas bottles”) to ensure that laser performance remains consistently optimal. Modern lasers typically have a gas lifetime of tens of millions of pulses; however, the specific replacement interval depends on the actual frequency of use and the results of performance monitoring.

Important Note: Due to the corrosive and toxic nature of chlorine gas, the filling, replacement, and disposal of used cylinders containing mixed gases must be carried out strictly in accordance with safety procedures by personnel who have undergone specialized training, ensuring the safety of both personnel and equipment.

III. Summary: The Importance of Choosing High-Quality Mixed Gases

A high-performance 308nm excimer laser relies not only on sophisticated optical and circuit designs but also on stable, pure, and precisely proportioned mixed gases. High-quality mixed gases can bring you:

• Stable output power: Ensures consistent and reliable treatment or processing results.

• Long service life: Reduces replacement frequency, lowers long-term operating costs, and minimizes downtime.

• Equipment protection: High-purity gases can effectively reduce corrosion of the laser’s internal cavity and electrodes, thereby extending the service life of the core equipment.

Therefore, choosing a mixed-gas supplier with stringent quality control, extensive experience, and comprehensive services is a crucial step in ensuring the efficient and stable operation of your laser equipment.

Friendly reminder: The information above is for educational purposes only. For specific gas specifications, replacement cycles, and safe operating procedures, be sure to follow the official guidelines and recommendations provided by the manufacturer of your laser device.