Rare-gas Halide Excimer Lasers Research Articles

稀有气体卤化物准分子激光器工作气体实时补给技术

稀有气体卤化物准分子激光器工作气体实时补给技术

Modelling of short-pulse generation in rare-gas halide excimer lasers. Part II. Numerical investigation of KrF and XeCl lasers with a square-wave-driven Pockels modulator

Abstract The properties of short-pulse generation in KrF and XeCl lasers by fast mode locking using a square-wave-driven Pockels modulator are investigated numerically. The influence of the most important parameters of the laser system on duration and peak power of a pulse generated is analysed in detail. A comparison of an active and active–passive case of mode locking is also carried out. It is shown that the method considered can be an efficient way for picosecond pulse production in rare-gas halide excimer lasers enabling considerably shorter (∼ 10–20 times) and more powerful pulses than those attainable with conventional mode locking techniques used so far to be obtained.

Modelling of short-pulse generation in rare-gas halide excimer lasers. Part II. Numerical investigation of KrF and XeCl lasers with a square-wave-driven pockels modulator

The properties of short-pulse generation in KrF and XeCl lasers by fast mode locking using a square-wave-driven Pockels modulator are investigated numerically. The influence of the most important parameters of the laser system on duration and peak power of a pulse generated is analysed in detail. A comparison of an active and active–passive case of mode locking is also carried out. It is shown that the method considered can be an efficient way for picosecond pulse production in rare-gas halide excimer lasers enabling considerably shorter (∼ 10–20 times) and more powerful pulses than those attainable with conventional mode locking techniques used so far to be obtained.

Modelling of short-pulse generation in rare-gas halide excimer lasers I. The model and its verification

Modelling of short-pulse generation in rare-gas halide excimer lasers I. The model and its verification

Modelling of short-pulse generation in rare-gas halide excimer lasers I. The model and its verification

In part I of this paper, a comprehensive model of a short-pulse rare-gas halide excimer (RGHE) laser consisting of excimer systems with the ground state both unbound and bound is presented. It takes into account the most important fast relaxation processes occurring in the active medium, variable cavity losses programmed externally, practical layout of the cavity elements, and also nonlinear saturable and non-saturable absorption in the laser. General equations for a short-pulse RGHE laser as well as their simplified variants for KrF and XeCl lasers are formulated. Good correspondence of the model to the results of numerous experiments described in the literature is demonstrated. In part II, the model will be applied in numerical investigations of short-pulse generation in KrF and XeCl lasers by fast mode locking using a square-wave-driven Pockels modulator.

Rate equations for modelling of short-pulse rare-gas halide excimer lasers

In this work, on the basis of the analysis of data relating to relaxation processes and emission spectra of excimer molecules, the rate equations for modelling short-pulse rare-gas halide excimer lasers are formulated and discussed. The equations take into account relaxation processes important for short-pulse generation, such as decay of B-, C- and X-states, vibrational relaxation in these states, and B-C mixing. As a special case for these equations, simplified equations for KrF and XeCl lasers are introduced. The gain recovery curves and the dependences of saturation energy on pulse duration, computed both for KrF and XeCl, coincide well with the experimental data. Discussion of the factors influencing the gain dynamics and the saturation energy of these media, is also presented.

Principles of Excimer Light Sources.

Excimer lasers and excimer lamps provided efficient and high-power UV sources for applications of laser-induced chemistry and laser processing. After the emission mechanism of excimers and the spectroscopy of excimers were briefly reviewed, excitation methods and system constructions of excimer lasers were described. Especially for discharge-pumped rare-gas halide excimer lasers, detaild description of laser system, gas treatment and simulation analysis was made.

High-Efficiency Discharge Excited Rare-Gas Halide Excimer Lasers.

Discharge excited rare-gas halide excimer lasers are useful for material processing such as lithography for next generation LSl, laser ablation of polymers and annealing for Si TAT. Among rare-gas halide excimer lasers, three lasers, XeCl, KrF and ArF lasers, are of practical use.In the present paper, basic parameters, which decide the characteristics of these three lasers, are clarified to be the breakdown voltage Vb, excitation duration ts and excitation power density WDE. A guide line to achieve a high oscillation efficiency for the three lasers using a capacitor-transfer-circuit and UV automatic preionization are presented, by considering the three basic parameters. We have obtained a high efficiency of 2.2% for a XeCl laser, 5% for a KrF laser and 2.3% for an ArF laser.The present study is useful to obtain high performance excimer lasers, bacause high-repetition, long-gas-lifetime and compact excimer lasers have been obtained by achieving a high oscillation efficiency.

Investigation of electron density and velocity distribution in high-pressure discharges for excimer laser pumping using laser Thomson scattering

Thomson scattering from plasmas in high-pressure discharges for rare-gas halide excimer laser pumping was observed using an yttrium-aluminum-garnet laser with a second harmonic generator, combined with a double-monochromator to reject large signal from Rayleigh scattering. The results showed the electron velocity distribution to be Maxwellian which was different from prediction of computer simulations, while variation of electron density and temperature with time and gas composition was consistent with results of computer simulations.

157 nm F2 Lasers.

Current research activities on the electric discharge pumped molecular fluorine lasers at 157 nm, and the present understanding for the laser kinetics are reviewed. Fast and intense discharge excitation, which is more than one order of magnitude higher than excitation rates used for conventional rare-gas halide excimer lasers, improved both output laser energy (100-200 mJ) and efficiency (up to 0.4 %). Successful introduction of cryogenic gas purification that traps various impurity molecules introduced by gases supplied or by secondary reactions during the discharge extended the F2 laser gas lifetime to > 5×105 shots. Further development of high repetition rate high-power exciters, excellent optics with higher damage thresholds, and large aperture and well-controlled low divergence laser beams will open up various useful applications in photochemistry or photo ablation processes.

Determination of electron density in discharge-pumped excimer laser using Stark broadening of Hβ line

The determination of the electron density in the discharge plasma used for the compact discharge-pumped rare-gas halide excimer laser of capacitor transfer type with automatic preionization was performed first by measuring the Stark half-width of the Hβ line. For the discharge-pumped XeCl laser at a total gas pressure of 2 atm and a charging voltage of 20 kV, the measured electron densities were 2.1×1015 cm−3 for Ne diluent and 1.7×1015 cm−3 for He diluent.

Simultaneous multiwavelength operation of a commercial rare gas halide laser

Simultaneous dual wavelength operation of a commercial-discharge excited rare gas halide excimer laser is reported for the first time. A combined energy output in excess of 20 mJ was obtained for the 193 and 248 nm ArF and KrF <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B \rightarrow X</tex> transitions oscillating simultaneously, and also for the 248 and 351 nm KrF and XeF transitions. Analysis indicates that significantly higher dual wavelength energies should be possible.

Broadband Tunable XeF (C→A) Excimer Laser

In this paper the factors controlling the performance of an electron beam pumped broadband diatomic raregas halide excimer laser are discussed. Particular attention is directed toward the blue/green in the XeF (C-A) laser centered at 485 nm, for which significantly improved performance has been obtained by selective tailoringof mixture kinetic processes. Maximum XeF (C-A) laser output energy densities in excess of 3 J/liter have beenachieved, corresponding to an intrinsic efficiency of approximately 2%.

Deep UV exposure of Ag2Se/GeSe2utilizing an excimer laser

Although inorganic resists are characterized by high contrast and resolution, they have traditionally suffered from poor sensitivity. We have investigated the use of a rare-gas halide excimer laser operating at λ = 249 nm to expose the inorganic resist Ag <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Se/GeSe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . Well-controlled lines and spaces, each of 0.5-µm width, were contact printed using a chromium-on-quartz mask. By increasing the peak dose rate to about 520 kW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , we found that the required dose could be lowered from 130 to 5.2 mJ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ; this sensitivity is a factor of 250 better than that obtained with exposures at λ = 436 nm and low power densities. The reciprocity failure at these high flux rates can be explained by a locally induced temperature rise.

Development of Excimer Lidar System with a Wide Wavelength Range for Upper Atmospheric Research

Excimer lidar system is developed for middle atmospheric research. The characteristic is a wide wavelength range from UV to visible. The transmitter based on the efficient high power rare-gas halide excimer lasers such as XeCl, and XeF lasers. Tunable dye lasers are pumped by a XeCl laser and Raman lasers of high-pressurized H2 and CH4 gases are pumped by a KrF laser. The part of the receiver system consists of a 50-cm diameter telescope and two photon counters with a floppy memory disk. Preliminary measurement results of stratospheric ozone and aerosol are described. The measurement error analysis tropospheric ozone by Raman, lasers based on the differential absorption lidar technique is discussed. Measurement possibilities of atmospheric density and temperature above 30km with high accuracies will be denoted. This lidar system add new possibilities for monitoring atmospheric constituents.

Pulsed Glow Discharges in Laser Excitation and Breakdown

The spatiotemporal development of discharges in uniform field gaps has been studied for many years in order to understand the physical mechanisms of breakdown. These studies have shown that a glow discharge structure is produced as an intermediate stage in the breakdown process which finally leads to the formation of a filamentary arc. Recently these pulsed or transient glow discharges have been used to pump a wide variety of gas lasers including CO2 lasers and rare gas-halide excimer lasers. Preionization of the gas volume is usually used to ?stabilize? these laser glow discharges, i.e. to increase the duration and/or energy density of the pulsed glow discharge and delay the onset of arc formation. Recent experimental work also has shown that the corona discharges which are observed in point-plane gaps have a glow discharge-like structure. These two types of discharges are compared and some speculations are offered about the ?corona stabilization? process in point-plane gaps and its relationship to arc formation in uniform field gaps.

A narrow bandwidth, pulsed, ultra-violet dye laser

A simple, narrow bandwidth, dye laser using para-terphenyl and operating in the region 3350–3450 Å is described. The laser incorporates beam expansion at a grazing incidence diffraction grating and is pumped by a rare gas halide excimer laser. Output bandwidths as low as 0.012 Å have been obtained.

Applications of excimer lasers to laser-radar observations of the upper atmosphere

Development of efficient ultraviolet (UV) rare-gas halide excimer lasers has added new possibilities for laser radar (lidar) technique for monitoring atmospheric constituents. An experimental result of the observation of the stratospheric ozone layer by a XeCl laser (308 nm) based on the differential-absorption-lidar (DIAL) technique is described. The obtained ozone profile in an altitude range of 15- 25 km are in good agreement with those measured by radiosonde. The measurement error is analyzed for one-wavelength lidar. The accuracy is estimated to be 10-30 percent within an altitude range of 10-30 km and at a range resolution of 1 km or less. The accuracy and the resolution are higher than the Umkehr method. Recent progress of rare-gas halide lasers and their frequency conversion techniques as a transmitter for lidar are reviewed. Many powerful and reliable new sources are available in almost every wavelength over the near UV region. New applications of these UV sources to the lidar system are also briefly discussed, especially from the scientific field on the middle atmosphere.

Operating and beam characteristics, including spectral narrowing, of a TEA rare-gas halide excimer laser

A simple TEA excimer laser has been developed having a fast discharge with distributed preionization. The output pulses are short (∼7 ns), of high peak power (5-15 MW), and good reproducibility. Narrow linewidth (<1 cm-1), and tunability (∼0.8 nm) have been obtained with KrF using a grating at grazing incidence.

Transient absorpion following flash photodissociation of halogens in rare gases

Flash photodissociation of Cl 2 in Kr, and Cl 2, Br 2 or I 2 in Xe, leads to transient UV absorption bands attributed to contact charge-transfer interaction between ground-state rare-gas and halogen atoms. With XeCl or XeBr strong, narrowband absorptions occur precisely at the rare-gas halide excimer laser wavelengths.