Excimer laser systems are characterized by a number of physical and operational parameters. The following terminology explains commonly used terms and specifications associated with excimer laser technology.
Understanding Excimer Laser Terminology
Excimer laser systems are defined by a combination of electrical, optical, and plasma-related parameters that directly influence performance and process outcomes. Understanding how these parameters relate to each other is essential for specifying systems, designing processes, and interpreting application results.
The terminology in this section links fundamental laser physics with system behavior and application requirements. Each definition is intended to provide both, a physical explanation and a practical reference for working with excimer-based UV technologies.
Key Terms used in Excimer Technology
Laser Pulse Parameters
Energy contained in a single laser pulse.
In excimer lasers generally determined by discharge energy.
Unit: mJ
Related terms: Fluence, Extraction Efficiency
Temporal width of the laser pulse, typically specified as full width at half maximum (FWHM).
Compact excimer lasers typically generate pulses in the 5–10 ns range.
Related terms:
Repetition Rate, Pulse Energy
Number of laser pulses emitted per second.
In excimer lasers limited by gas recovery dynamics and discharge thermal load.
Unit: Hz
Related terms:
Duty Cycle, Thermal Load
Maximum fraction of time a laser can operate at full repetition rate and pulse energy without exceeding thermal limits.
For compact excimer lasers, the duty cycle is primarily determined by discharge heating and cooling capacity and may be extended by dedicated cooling regimes.
Related terms:
Repetition Rate, Pulse Energy, Thermal Load
Heat generated within the laser during operation, primarily from electrical discharge energy. Excimers only convert about 1% into laser radiation.
Thermal load determines cooling requirements and influences repetition rate and duty cycle limits.
Related terms:
Duty Cycle, Repetition Rate, Laser Efficiency
Variation of pulse energy between consecutive laser pulses.
Primarily influenced by discharge uniformity and preionization.
Related terms:
Pulse Energy, Stabilized Energy, Preionization
Maximum pulse energy maintained by the laser’s internal energy stabilization control.
Defines the stable operating point specified.
Related terms: Pulse Energy, Energy Stability
Beam Properties
Spatial energy distribution across the laser beam cross-section.
Compact excimer lasers typically produce rectangular beams (long axis: top-hat, short axis: gaussian profile), for example 6 × 3 mm.
Related terms:
Fluence, Beam Divergence
Angular spread of the beam during propagation.
Important paramter for beam path design conisderations.
Unit: mrad
Related terms:
Beam profile, Fluence
Laser pulse energy delivered per unit area.
F= E/A
Primary parameter governing UV photochemical and ablation processes.
Unit: mJ/cm²
Related terms: Pulse Energy, Beam Profile
Spectral width of the emitted radiation.
Excimer lasers typically emit ultraviolet radiation defined by molecular transitions, e.g. for ArF lasers the linewidth is around 0.5 nm.
Related terms:
Coherence Length
Gas & Plasma Physics
Gas mixture used in excimer lasers consisting of noble gas, halogen donor, and buffer gas.
Gas composition strongly influences gain and discharge stability.
Related terms:
Buffer Gas, Excimer
Inert gas controlling pressure and discharge characteristics.
Excimer lasers commonly use neon as buffer gas.
Related terms:
Premix, Discharge Voltage
Generation of free electrons prior to the main discharge to ensure homogeneous plasma formation (excitation of the laser gas mixture).
Compact excimer lasers commonly use corona preionization for stable discharge.
Related terms: Discharge Voltage, Paschen’s Law
Electrical potential applied across the electrodes to initiate the gas discharge.
Determined by gas composition, pressure, and electrode spacing.
Related terms:
Paschen’s Law, Preionization
Relationship between gas pressure, electrode distance, and electrical breakdown voltage.
Defines discharge ignition voltage in gas lasers.
Related terms:
Discharge Voltage
Collisional de-excitation of excited molecules without laser emission.
Reduces laser efficiency by suppressing stimulated emission.
Related terms:
Excimer, Gain, Stimulated Emission
Process where electrons recombine with positive ions in the plasma.
Influences charge balance and discharge stability.
Related terms:
Discharge Voltage
Laser Physics
Short-lived excited molecular complex formed from noble gas and halogen atoms.
Stable only in the excited state and dissociative in the ground state.
Related terms:
Population Inversion, Stimulated Emission
Condition where the population of excited states exceeds that of lower energy states. Required for optical gain and laser amplification.
Related terms:
Stimulated Emission, Gain
Photon emission triggered by an incident photon of identical energy and phase.
Enables coherent optical amplification inside the laser cavity.
Related terms:
Population Inversion, Gain
Random photon emission during transition from an excited state to a lower energy state.
Provides initial photons that seed stimulated emission.
Related terms:
Stimulated Emission, Einstein Coefficient
Amplification of optical radiation in the laser medium.
In excimer lasers relatively high gain occurs during the pulsed gas discharge.
Related terms:
Population Inversion, Optical Resonator
Amplification of optical radiation in the laser medium.
In excimer lasers relatively high gain occurs during the pulsed gas discharge.
Related terms:
Population Inversion, Optical Resonator
Resonator Configuration
Arrangement of mirrors providing optical feedback for laser oscillation.
Defines mode structure and output characteristics.
Related terms:
Plan-Plan Resonator, Output Coupling
Resonator consisting of two parallel mirrors.
Common in excimer lasers due to high gain and short cavity lengths.
Related terms:
Optical Resonator, Output Coupling, Gain
Fraction of intracavity radiation extracted through the output coupler (which usually is a partial reflective mirror). Typical values for excimers are 50-90%.
Balances resonator gain and usable output energy.
Related terms:
Laser Efficiency, Optical Resonator
Ratio of emitted laser energy to electrical discharge energy.
Indicates efficiency of converting electrical excitation into laser radiation.
Typical values for excimer lasers are within 1-3%.
Related terms:
Output Coupling, Optimal Efficiency
UV Interaction
Energy carried by a single photon of electromagnetic radiation.
E = h × c/λ
Shorter UV wavelengths correspond to higher photon energies and stronger interaction with many materials. Typical values are 6.42 eV for 193 nm and 5.0 eV for 248 nm.
Related terms:
Absorption Coefficient, Fluence
Measure of how strongly a material absorbs radiation.
Important when designing UV optical systems and process windows.
Related terms:
Photon Energy, Fluence
Distance between two components of the emitted radiation that maintain a stable phase relationship.
Typically shorter for excimer lasers than for single-frequency solid-state lasers.
Related terms:
Linewidth
Frequently Asked
Excimer lasers generate ultraviolet radiation through a pulsed gas discharge that forms short-lived excited molecules. These excimer states create population inversion and optical gain. Inside the resonator, stimulated emission amplifies this radiation into nanosecond laser pulses.
Related terms:
Excimer, Population Inversion, Stimulated Emission, Gain
Excimer lasers rely on transient molecular states formed in rare-gas/halogen mixtures. These excited molecules exist only in the plasma, generated by a pulsed gas discharge, making gas excitation the most effective way to produce high-energy ultraviolet laser pulses.
Related terms:
Premix, Excimer, Discharge Voltage, Preionization
Preionization creates a uniform population of free electrons before the main discharge begins. This prevents localized breakdown and ensures homogeneous plasma formation across the electrodes, which is essential for stable pulse energy and reproducible beam characteristics.
Related terms:
Preionization, Discharge Voltage, Paschen’s Law
Excimer molecules form only when atoms are electronically excited. In their ground state the atoms repel each other and immediately dissociate. This unique property enables efficient ultraviolet emission.
Related terms:
Excimer, Quenching, Spontaneous Emission
Excimer lasers operate most reliably within a defined high-voltage range where discharge dynamics and gas chemistry remain stable. Energy monitoring systems regulate the high voltage to ensure consistent performance and predictable processing conditions. Therefore, the maximum stabilized energy indicates where pulse characteristics, beam behavior, and long-term operation are stable for continuous operation.
Related terms:
Pulse Energy, Energy Stability, Stabilized Energy
Fluence describes how much laser energy reaches a given surface area. For a fixed beam size, higher pulse energy directly increases fluence. In ultraviolet processing this parameter determines whether a material is modified, ablated, or unaffected.
F = E / A
Related terms:
Pulse Energy, Fluence, Beam Profile
Excimer media provide very high optical gain over short distances. This allows simple resonator geometries such as parallel mirrors. The configuration is mechanically robust and supports efficient extraction of high-energy ultraviolet pulses.
Related terms:
Plan-Plan Resonator, Gain, Output Coupling
Ultraviolet photons carry relatively high energy. Many polymers, biological materials, and surface layers strongly absorb this radiation, enabling precise photochemical modification or ablation with minimal thermal penetration into surrounding material.
Related terms:
Photon Energy, Fluence, Absorption Coefficient
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