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Interaction of intense ultrashort laser pulse with gases generates a transient spatiotemporal electron density distribution via field ionization, which may lead to the spatiotemporal reshaping of the pulse, viz., its beam profile, pulse width, etc. Here, we present an experimental study on ultrashort laser pulse interaction with argon gas sheath in an ionization saturation intensity regime (∼1015–1017 W/cm2). The present investigation has been performed using a 6 mJ, 1 kHz, and 55−60 fs Ti:Sapphire laser pulse interaction with a ∼2.5 mm long argon sheath. After the laser gas interaction, the laser spatial profile exhibits a multi-ring structure around a central maximum spot. Laser gas interaction parameters, such as laser intensity, gas pressure, etc., affect the ring pattern significantly. Under optimum parameter conditions, the laser pulse has two rings in spatial profile, and the pulse width of the central spot is self-compressed to ∼35 fs. A theoretical calculation reveals that the laser beam's spatiotemporal profile evolves as it propagates inside the gas sheath. The calculation also demonstrates that the gas ionization profile plays a crucial role in the spatiotemporal reshaping and self-compression of the laser beam. The calculation also shows that the generation of concentric ring patterns in the spatial profile is mainly due to the ionization of argon atoms into Ar+, Ar2+, and Ar3+ species in the interaction region. Such self-compressed laser pulses with concentric ring beam profiles may be useful for high-harmonic generation and shorter attosecond pulse trains. [ABSTRACT FROM AUTHOR]

Diode-pumped rare gas lasers (DPRGLs) have the potential for high-energy laser output with high beam quality. The metastable concentration >1014 cm−3 and pump intensity >10 kW/cm2 are required in developing high-power and efficient DPRGLs. However, the kinetics of 1s and 2p levels (Paschen notation) under these conditions is unclear yet, particularly regarding the adverse effects of interference energy levels (e.g., 1s4 and 2p1–2p8). This study addresses this gap by measuring the number densities of 1s and 2p levels in a diode-pumped plasma jet metastable argon laser. The experiment was conducted with a much higher number density of 1014 cm−3 and a higher pump intensity of 12 kW/cm2 than our previous works. The results indicate that the adverse effect of 1s4 accumulation could be partially compensated, and the relative population distribution of 2p energy levels remained unchanged. However, the high gas temperature (>1000 K) caused a significant negative impact of high 2p levels (2p1–2p8), and the air environment weakened the effect of He collision relaxation. [ABSTRACT FROM AUTHOR]

Short pulses of millimeter wave (MMW) radiation at 43 GHz create microplasma within a photonic crystal for pressures from 40 to 600 Torr (1.3 × 103–8.0 × 104 Pa). Gas breakdown occurs within a photonic crystal, which acts as an electromagnetic resonator to create a strong initial electric field. The time response of the argon metastable density is experimentally determined during the pulse and in the afterglow using laser absorption. The metastable density overshoots the steady-state condition at the beginning of the pulse and during the afterglow. Modeling is presented to understand these observations. The overproduction of argon 1s5 at the beginning of each pulse is due to a concurrent overshoot in the MMW electric field within the photonic crystal. This field overheats the plasma electrons and enhances the production of excited states. The burst of argon metastables observed in the afterglow is due to the pooled energy of the plasma stored in electrons, ions, and excited states of argon. Understanding metastable production is an important intermediate step to ionization and is also critical in the study of diode-pumped rare gas lasers. [ABSTRACT FROM AUTHOR]

Diode-pumped metastable rare gas lasers are showing their potential for high-energy laser systems with intensive investigations carried out to understand their lasing characteristics. Here, we demonstrated pulsed lasing of a diode-pumped argon metastable laser based on a pulsed DC glow discharge in argon and helium mixtures for different discharge voltages and pressures. A transient rate equation model was established and solved to explain the cause of the pulsed lasing in our experiment. The insufficient production rate of argon metastable atoms (1s5) and the slow transfer rate out of the 1s4 state in the plasma during the lasing process were found to be the key reasons. This work may shed some light on the future design of plasma sources that have higher metastable atom production rates to achieve highly efficient continuous wave lasing. [ABSTRACT FROM AUTHOR]

The optically pumped rare gas laser (OPRGL) is an innovative type of gas laser, which has the potential to be a candidate for high-energy lasers (HELs), in which metastable rare gas atoms generated by gas discharge are used as active particles. To realize these kinds of lasers as HELs in field application, high efficiency and low cost are necessary. For this purpose, we demonstrated a closed-chamber operation with repetitively pulsed gas discharge for an OPRGL of argon metastables. The pulsed discharge was powered by a home-made LC generator, which provided a high efficiency for the deposition of electric energy. The metastable density produced was higher than 1012 cm−3, quite enough for efficient laser operation. The dependencies of laser radiation on the parameters of discharge voltage, gas pressure, and argon concentration were studied, which showed an optimized argon concentration of 1%. Long-time operations were also performed, which demonstrated the practicability of the operation of OPRGL in a closed chamber, with the avoiding of the running away of rare gases in the open cycle of flowing operation. [ABSTRACT FROM AUTHOR]

Optically pumped rare gas laser systems require a lasing medium of high density metastable atoms. A scalable two-dimensional array of quarter-wave resonators produces high microwave electric fields suitable for generating a dense gas of argon 1 s 5 states. This resonator array is immersed within an evacuated waveguide in order to create a volume of plasma in a relatively wide discharge gap (13 mm) at argon-helium pressures up to 100 Torr using 30 W of continuous microwave power at 2.3 GHz. Spatial density profiles of argon 1 s 5 states are measured using diode laser absorption spectroscopy with 0.5 mm resolution. The region of argon 1 s 5 states is mapped in the discharge and shown to have an estimated density in excess of 1 × 10 18 m − 3 within a volume of 11.6 × 3.2 × 0.8 m m 3. [ABSTRACT FROM AUTHOR]

Multiple deleterious processes occurring in alkali vapor laser amplifiers can significantly degrade their performance. To study that, a theoretical model of a side-pumped flowing-gas alkali vapor amplifier is set up, which mainly takes into account the effect of saturation, amplified spontaneous emission, quenching, energy pooling, photoexcitation, Penning ionization, photo-ionization, and ion recombination. Influences of powers of the pump and seed laser, the velocity of gas mixture flow, and the cell length on the deleterious processes are also simulated. The results show that the influence of deleterious processes can be increased when pump power enhances. But it can be effectively restrained with relatively strong seed laser power and optimized operating parameters. The total percent drop in amplified laser power is about 19.95% at a pump power of 500 W, a seed laser power of 5 W, a saturated flowing velocity of 40 m/s, and an optimized cell length of 7 cm. [ABSTRACT FROM AUTHOR]

Wavelength-matched vibrational excitations of ethylene (C2H4) molecules using a tunable carbon dioxide (CO2) laser were employed to significantly enhance the chemical vapor deposition (CVD) of diamond in open air using a precursor gas mixture of C2H4, acetylene (C2H2), and oxygen (O2). The CH2-wag vibration mode (ν7) of the C2H4 molecules was selected to achieve the resonant excitation in the CVD process. Both laser wavelengths of 10.591 and 10.532 μm were applied to the CVD processes to compare the C2H4 excitations and diamond depositions. Compared with 10.591 μm produced by common CO2 lasers, the laser wavelength of 10.532 μm is much more effective to excite the C2H4 molecules through the CH2-wag mode. Under the laser irradiation with a power of 800 W and a wavelength of 10.532 μm, the grain size in the deposited diamond films was increased by 400% and the film thickness was increased by 300%. The quality of the diamond crystals was also significantly enhanced. [ABSTRACT FROM AUTHOR]

We present experimental and theoretical studies of nanosecond ArF excimer laser desorption and ablation of silicon with insight into material removal mechanisms. The experimental studies involve a comprehensive analysis of the laser-induced plume dynamics and measurements of the charge gained by the target during irradiation time. At low laser fluences, well below the melting threshold, high-energy ions with a narrow energy distribution are observed. When the fluence is increased, a thermal component of the plume is formed superimposing on the nonthermal ions, which are still abundant. The origin of these ions is discussed on the basis of two modeling approaches, thermal and electronic, and we analyze the dynamics of silicon target excitation, heating, melting, and ablation. An electronic model is developed that provides insight into the charge-carrier transport in the target. We demonstrate that, contrary to a commonly accepted opinion, a complete thermalization between the electron and lattice subsystems is not reached during the nanosecond-laser pulse action. Moreover, the charging effects can retard the melting process and have an effect on the overall target behavior and laser-induced plume dynamics. [ABSTRACT FROM AUTHOR]

Magnetically confined laser-induced breakdown spectroscopy was investigated by studying the optical emission from laser-induced plasma plumes expanding across an external transverse magnetic field. KrF excimer laser pulses with a pulse duration of 23 ns and a wavelength of 248 nm were used to produce plasmas from Al, Cu, and Co targets. Various optical emission lines obtained from Al and Cu targets show an obvious enhancement in the intensity of optical emission when a magnetic field of ∼0.8 T is applied, while the optical emission lines from Co targets show a decrease in the optical emission intensity. The enhancement factors of optical emission lines were measured to be around 2 for the Al and Mn (impurity) lines from Al targets, and 6–8 for Cu lines from Cu targets. Temporal evolution of the optical emission lines from the Al samples shows a maximum enhancement in emission intensity at time delays of 8–20 μs after the incident laser pulse, while from the Cu targets it shows a continuous enhancement at time delays of 3–20 μs after the pulse. The enhancement in the optical emission from the Al and Cu plasmas was presumably due to the increase in the effective plasma density as a result of magnetic confinement. The decrease in the emission intensity from the Co plasmas was suggested to be due to the decrease of effective plasma density as a result of the magnetic force. [ABSTRACT FROM AUTHOR]

Ne–Kr gas mixtures with high Kr concentrations were applied to ac plasma display panels. Spatiotemporal behaviors of excited Kr atoms in the 1s5 metastable state and the 1s4 resonance state were measured by microscopic laser-absorption spectroscopy in the binary mixtures with Kr concentrations of 20% and 40%. A systematic comparison was done between the characteristics of Ne–Kr-filled panels and those of conventional Ne–Xe panels with the same structure but with lower Xe concentrations of 5% and 10%. For example, the total number of Kr*(1s5) atoms in a unit cell ranged from 7.4×107 to 2.0×108, at the peak was apparently smaller than the value of Xe*(1s5) atoms. However, when the difference in the decay rate of the excited atoms by three-body collision processes is taken into account, the production efficiency of vacuum-ultraviolet (VUV) emission from Kr2* excimers is as large as that from Xe2* excimers in a usual panel since these processes lead directly to the formation of excimers. From the measured density of Kr*(1s4) atoms, it is estimated that the contribution of the atomic resonance line is smaller than the excimer band at those high Kr concentrations. In any case, by summing up those two contributions to the VUV emission, the overall efficiency in the Ne–Kr(40%) panel is estimated to be comparable to that in the Ne–Xe(10%) one. [ABSTRACT FROM AUTHOR]

Postimplantation thermal processing of Be in molecular-beam-epitaxy-grown GaN by rapid thermal annealing (RTA) and pulsed laser annealing (PLA) was investigated. It has been found that the activation of Be dopants and the repair of implantation-induced defects in GaN films cannot be achieved efficiently by conventional RTA alone. On the other hand, good dopant activation and surface morphology and quality were obtained when the Be-implanted GaN film was annealed by PLA with a 248 nm KrF excimer laser. However, observations of off-resonant micro-Raman and high-resolution x-ray-diffraction spectra indicated that crystal defects and strain resulting from Be implantation were still existent after PLA, which probably degraded the carrier mobility and limited the activation efficiency to some extent. This can be attributed to the shallow penetration depth of the 248 nm laser in GaN, which only repaired the crystal defects in a thin near-surface layer, while the deeper defects were not annealed out well. This situation was significantly improved when the Be-implanted GaN was subjected to a combined process of PLA followed by RTA, which produced good activation of the dopants, good surface morphology, and repaired bulk and surface defects well. [ABSTRACT FROM AUTHOR]

The air oxidation kinetics of low coverages of ∼5 nm Si nanoparticles, deposited by pulsed excimer laser ablation (KrF, 248 nm) in He, have been characterized by x-ray photoelectron spectroscopy. A simple model, based on the evolution of the Si 2p spectral components during oxidation, has been developed to determine the nanoparticle oxide thickness. It is found that the short-term oxide thickness is greater, and the long-term room-temperature air oxidization rate of these nanoparticles is less, than those reported for bulk a-Si and c-Si. The results are also consistent with an earlier transmission electron microscope observation of the oxidation of larger Si particles at higher temperatures. The greater short-term oxide thickness may be attributed to surface defects on the prepared Si nanoparticles, and lower long-term oxidation rate is due to the nonlinear decrease of oxygen diffusion in spherical systems. [ABSTRACT FROM AUTHOR]

Uniaxial tensile deformation of oxidized aluminum produces low work-function patches of fresh metal which can be probed by measurements of photoelectron emission during exposure to ultraviolet light. We report measurements of photoelectron emission during uniaxial testing of polycrystalline Al(1200), Al–Mn(3003), Al–Mg(5052), and Al–Mg–Si(6061) alloys where the broad face of the gauge section is exposed to pulsed excimer laser radiation (248 nm). We show that strain localization alters the distribution of fresh surface metal produced by subsequent deformation. The transition from more homogenous deformation to the principally localized deformation associated with shear bands is associated with a discontinuity in the growth rate of photoelectron intensities versus time. At this transition, the rate of fresh metal production along the illuminated portion of gauge section decreases. In all four materials, the strain at the discontinuity is somewhat below the strain given by the Considère criterion, consistent with the role of microstructural effects in strain localization. We suggest that these photoelectron measurements constrain quantitative models of strain localization. [ABSTRACT FROM AUTHOR]

An atomic force microscopic method to study the incubation states of UV laser irradiated polymer samples is presented. Targets were illuminated by different number of pulses at 5.8 and 8.9 mJ/cm2 fluences. The induced adhesive and morphological changes were investigated simultaneously by an atomic force microscope equipped with a pulsed force mode extension. Importantly, below 100 pulses morphological changes were not observable while significant changes in the adhesion were found as a result of the incubation at 8.9 mJ/cm2 fluence. This method allows the imaging and detection of the whole laser modified area with nanometer resolution. [ABSTRACT FROM AUTHOR]

Laser induced crystallization of hydrogenated amorphous silicon carbon alloy (a-Si1-xCx:H) films has been investigated by means of synchrotron x-ray diffraction. The a-Si1-xCx:H films were deposited on (100) silicon wafers by very high frequency plasma enhanced chemical vapor deposition at 100 MHz in hydrogen diluted silane-methane gas mixtures. The substrate was kept at 250 °C or 350 °C and the stoichiometry was changed from x=0.20 to 0.63. The structural characterization of the as-grown films has been carried out by Rutherford backscattering (hydrogen concentration) and infrared spectroscopy (film ordering). The films were irradiated by a KrF excimer laser (248 nm) with varying energy density and number of pulses. After irradiation, the formation of SiC crystallites has been revealed by synchrotron x-ray diffraction. Besides SiC nanocrystals, the formation of crystalline Si and graphite is observed for under-(x < 0.50) and over-stoichiometdc (x>0.50) samples, respectively. The essential role played by hydrogen concentration and hydrogen bonding configuration in determining the melting threshold and the consequent SiC grain formation is highlighted. [ABSTRACT FROM AUTHOR]

The electron deposition in an Ar-Kr-F[sub 2] mixture, based on a solution of the electron Boltzmann equation, is presented. The model is relevant to an electron-beam generated KrF* laser amplifier at atmospheric pressure. Sets of cross sections for Ar, Kr, and F[sub 2] have been compiled. Calculations have been performed to determine the electron energy distribution function, energy per electron-ion pair and the ionization and excitation rates. It is found that the inclusion of inner shell ionization and the subsequent Auger emission are essential for matching known results on both the energy per electron-ion pair W[sub ei] and the stopping power in pure Ar or Kr target gases. For the chosen Ar-Kr-F[sub 2] mixture, W[sub ei] is calculated to be 24.6 eV. The excitation-to-ionization ratio is calculated to be 0.38 for Ar and 0.54 for Kr at low input power density P[sub beam] ( 1 kW/cm[sup 3]). Both ratios increase with P[sub beam], particularly for Kr which attains 0.8 at 1 MW/cm[sup 3]. The dependency on P[sub beam] and the excitation efficiency for Kr is significantly higher than previously assumed in KrF* kinetic models. Results are also compared with the continuous slowing down approximation to demonstrate that this approach is limited to the regime of low power deposition. [ABSTRACT FROM AUTHOR]

Presents a study which examined the transient dynamics of multiplexed short-pulse amplification in krypton fluoride lasers. Background information on pulse compression scheme and amplification; Description of a numerical model; Results.

Presents a study which conducted a theoretical evaluation of the effect of buffer gases on the operating performance of a self-sustained discharge argon fluoride laser that use a charge transfer excitation circuit. Information on discharged-pumped argon fluoride lasers; Development of a kinetic model; Results and discussion.

Presents a study which modeled the properties of a transverse electron beam pumped argon ion laser with the use of Monte Carlo techniques. Description of a Monte Carlo model of electron pumping; Analysis of cross-sectional energy dependencies; Results and discussion.

Presents a study which examined the properties of shell confinement long-life plasmas produced by a carbon dioxide laser. Use of x-ray spectroscopic methods; Experimental results; Discussion and conclusions.

Describes the discharge properties of a formed-ferrite plasma source (FFPS) intended for gas laser applications. Plasma production process of the FFPS; Representative relationships between voltage and current waveforms which were measured simultaneously; Dependencies of the time of delay on the charging voltage.

Presents a study that investigated the resonator mode evolution in a krypton fluoride laser. Methodology; Analysis of the temporal and spatial behavior of the mode evolution; Examination of the intensity profiles of the laser beams.

Presents a study which examined the output energy characteristics of the pulsed, optically pumped 4.3-µmeter carbon dioxide laser. Description of a rate-equation model; Experimental apparatus; Optimization of output energy.

Presents a study which generated silicon clusters by carbon dioxide laser-induced decomposition of SiH[sub4] in a flow reactor. Experimental details; Results and discussion; Conclusion.

Presents a radio frequency (rf) excitation system that can drive a gas laser constructed of multiple wide, but narrow-gap, discharge volumes. Reason for the difficulty of the attainment of multikilowatt radiation from a single slab; Derivation of independent coupling and rf power division for each electrode segment; Description of end feed.

Presents a study which performed spectroscopic measurements of laser induced plasma during welding with carbon dioxide laser. Experimental details; Results and discussion; Conclusion.

Studies the effect of a small admixture of high-Z atomic radiators on the radiation rate of a laser-produced nitrogen plasma for application to a nitrogen recombination soft x-ray laser. Information on gas jet laser target used in the experiment; Single-shot spectrum of pure nitrogen; Time dependence of soft x-ray emissions for pure and seeded nitrogen plasmas.

Discusses a study which examined the gain and saturation intensity of a multichannel extended-area discharge carbon dioxide laser. Theoretical background; Description of the experimental setup; Findings.

Presents a study that measured the gas temperature and electron density in the plasma of a copper-vapor laser. Use of iterative algorithm; Background on copper-vapor lasers; Demonstration of the cross analysis of the linewidth components for finding gas temperature and electron density.

Presents a study which performed time-resolved gain measurements of high-pressure ultraviolet-preionized self-sustained discharge pumped atomic xenon laser. Disussion of measured gains in conjuction with multiline laser oscilaltion performance; Experimental setup; Results.

Discusses the theoretical investigation and modeling of the discharge inductance of a spark gap in pulsed gas lasers. Illustration of the discharge channel and the Gaussian current distribution; Method for measuring spark-gap inductance; Mechanisms responsible for variations of the channel radius; Time history of the arc-channel cross section.

Discusses a study which described a two-dimensional model for transverse discharge-excited gas lasers. Accounts of related studies; Results; Conclusions.

Presents information on a study which examined the achievable beam quality resulting from heavy charged particle pumping of transverse flow, gas laser amplifiers. Methodology of the study; Results; Conclusion.

Focuses on a study which developed a cylindrical surface-discharge device to examine the photoinitiated gas laser schemes. Experimental procedures; Information on the discharge electrical properties of gas laser schemes; Discussion of gas dynamic behavior.

Focuses on a study which measured the output characteristics of an optically pumped titanium vapor laser on various buffer gas species and pressures. Role of buffer gas on the laser output; Elements used as buffer gases; Description of the optimum condition for the maximum output energy.

Presents a study which measured the generation of dirt spikes in the discharge of a clean pulsed metal vapor laser. Experimental details; Results and discussion; Conclusion.

Presents a study which examined lifetimes of cold cathodes for helium-neon gas lasers. Properties of cold cathodes; Significance of secondary emission caused by positive ion bombardment to cold cathodes; Details of the experimental techniques used.

In this study, the effects of a KrF excimer laser irradiation on the surface work function (SWF) of indium-tin-oxide (ITO) have been investigated. From the observed x-ray photoelectron spectroscopy results, optical transmittance measurements, and four-point probe measurements, it is suggested that the surface chemical changes, the reduction of the carrier concentration, and an increase in the sheet resistance had strong effects on the SWF of ITO. We find that the (O2)2- occupation of oxygen vacancies (VO2+) near the ITO surface after laser irradiation induced a peroxidic ITO surface, increasing the SWF. [ABSTRACT FROM AUTHOR]

Focuses on study which conducted spatially resolved transverse-gain profile measurements in radio frequency- and direct current-excited waveguidelike cavities for carbon dioxide laser gas mixtures. Requirements for spatially resolving the gain profile; Impact of the current density and gas temperature on the gain profile; Recommendations.

Presents a sealed-off transversely excited atmosphere (TEA) CO[sub2] laser with a gas internal coaxial circulation scheme. Advantages of the design over the conventional transverse gas flow TEA CO[sub2]; Output when the laser was operated at 33 hertz with pauses.

Presents a study that reported spectral widths for a high-pump power F[sub2] excimer laser operating at 3-10 atm pressure. Description of the F[sub2] excimer laser; Linewidth values that made reliable application of the F[sub2] laser difficult; Interferograms recorded with various free spectral ranges under different operating gas pressures in the laser.

Focuses on a study which developed a method of exciting a gas discharge with microwave radiation. Use of microwaves for the excitation of lamps and gas lasers; Details on the passage of plasma light; Mixture of chlorine and xenon gases.

Presents a study that investigated the krypton fluoride laser -induced ablation and patterning of yttrium-barium-copper-oxide superconductor films. Methodology; Analysis of the different regimes of laser-material interactions; Examination of the transition temperatures and critical current densities of the samples.

Presents information on a study which observed the action of YAG-laser-vaporized metal-vapor laser. Description of the YAG laser; Methodology of the study; Results.

Simulations of an α-mode radio frequency dielectric barrier discharge are performed for varying mixtures of argon and helium at pressures ranging from 200 to 500 Torr using both zero and one-dimensional models. Metastable densities are analyzed as a function of argon-helium mixture and pressure to determine the optimal conditions, maximizing metastable density for use in an optically pumped rare gas laser. Argon fractions corresponding to the peak metastable densities are found to be pressure dependent, shifting from approximately 15% Ar in He at 200 Torr to 10% at 500 Torr. A decrease in metastable density is observed as pressure is increased due to a diminution in the reduced electric field and a quadratic increase in metastable loss rates through A r 2 * formation. A zero-dimensional effective direct current model of the dielectric barrier discharge is implemented, showing agreement with the trends predicted by the one-dimensional fluid model in the bulk plasma. [ABSTRACT FROM AUTHOR]

Presents a study which examined the effect of the choice of helium isotope on the output power of a sealed-off carbon dioxide laser. Function of helium in sealed-off carbon dioxide lasers; Methods; Experimental results.

Reports a power-enhanced nitrogen laser system which utilizes an autopreionization effect at the sharp edges of the Blumlein capacitor's electrode. Investigation of the enhancing effect of the laser; Schematic diagrams of the transversely excited atmospheric nitrogen laser system.