Effects of F- ions and F2 molecules on theoscillation process of a discharge-pumped ArF excimer laser

Time-resolved number densities of the fluorine negative ion in a discharge-pumped ArF excimer laser are measured by a dye laser absorption method. The peak density of F^- is 0.93 ×10 ¹⁵ cm^-3 at a total gas pressure of 2.5 atm, a gas mixture ratio of F₂-Ar-He=0.2-10.0-89.8, and a charging voltage of 28 kV for a 68-nF storage capacitor bank. The dependences of the peak F^- density and the ArF laser output power on the F ₂ gas fraction in F₂-Ar-He mixture are investigated. The effects of F^- ions and F₂ molecules on the ArF laser oscillation process are discussed by considering the F₂ mixture-ratio dependences of particle densities, laser output power, mean electron energy, and laser power extraction efficiency. With increasing F₂ mixing ratio, the ArF* excimer formation first increases as F^- increases, but in F₂-rich conditions the laser power decreases because of the laser photon absorption due to F^- ions and quenching of ArF* with F₂ molecules     

Theoretical high-efficiency extraction study of a short-pulseelectron-beam-pumped ArF laser amplifier with atmospheric pressureAr-rich mixtures

The single-pass (50 cm) amplifier performance of an atmospheric-pressure ArF laser pumped by a 65-ns full-width-at-half-maximum short-pulse electron beam was investigated theoretically for a wide range of excitation rates (0.1-2.0 MW/cm³ ). Atmospheric mixtures of Ne, Ar, and F₂ (three mixtures of Ar=40%, 70%, and Ne-free) were studied. A kinetic numerical model of the ArF amplifier with a Ne buffer system was constructed. A one-dimensional propagation treatment considered the gain depletion and saturation absorption spatially and temporally along the optical axis. In this model the rate constants for electron quenching of ArF* of 1.6×10^-7, 1.9×10^-7, and 2.4×10 ^-7 cm³/s were used for Ar concentration of 40, 70 percent, and Ar/F₂ mixture, respectively     

Saturation studies of the E-beam sustained discharge atomic xenonlaser

In an electron beam sustained discharge xenon laser the discharge energy deposition has been varied in order to investigate the saturation effect on the xenon laser. The current density of the electron beam is varied separately in the range of 0.1-2.7 A/cm² to obtain optimized discharge excitation conditions as a function of electron beam current density and gas pressure. An optimal fractional ionization f=3.5-4×10^-5 is found, independent of the electron beam parameters. The synergy of electron beam and discharge excitation has resulted in a maximum specific energy of 15 J/l at a total gas pressure of 9 bar     

Gain characteristics of an atmospheric sealed CW CO2laser

Experimental and analytical investigations have been made on unsaturated gain g0of a CO2electric-discharge convection laser, in which discharge current flow, gas flow, and the optical axis are mutually perpendicular. Stable glow discharges in sealed gas mixtures of CO2, CO, N2, and He were maintained at pressures up to 780 torr with an input power density of about 90 W/cm³. The ratio of electric field to neutral particle densityE/Nwas1.7 times 10^{-16}V . cm²and was independent of the total gas pressureP. The electron density in a positive column of the glow discharge was about4 times 10^{10}cm^-3. Detailed spatial distributions of g0at a wavelength near 10.6 μm were measured in the pressure range from 100 to 780 torr. Measurements were also made on the current dependence of g0and on the change in gowith discharge time. The g0distributions along the gas flow direction were found to agree with those calculated from the electron density distribution and the relaxation rate constant of the upper laser level on the basis of continuity equations for a two-level model. The integrated value of g0along the flow direction was proportional to P^-0.8whenE/N, electron density, and gas temperature were held constant. A maximum value of the g0distribution, which was proportional to P^-0.3, was 0.14 percent/cm at 780 torr.     

Diagnostics of TM010-mode microwave cavity discharges inCO2-N2-He laser gas mixtures. I. Measurement ofdielectric constant

Plasma parameters in the microwave discharged CO₂ laser gas mixtures of CO₂-N₂-He=0.9/2.5/20 at 25 Torr obtained using the perturbation method for a TM₀₁₀-mode cylindrical resonant cavity were examined. From the changes in resonant frequencies and Q values of the cavity, dielectric constant of the discharged plasma under the condition of RF to laser output power conversion ratio of 14% at mass flow rate of 4.2 kg/h was determined to be nearly 0.96-0.01j. It was also obtained from the dielectric constants of the plasma that electron number density, the electron temperature, and discharge parameters (E/n) were (0.3-3)×10¹⁵m^-3, 0.5-2.7 eV, and (0.5-2)×10^-15 Vcm², respectively     

Scaling characteristics of the XeF (C→A)excimer laser

The scaling characteristics and medium properties of an injection-controlled XeF(C→A) laser pumped by a 10-ns-high current density electron beam have been investigated. A five-component laser gas mixture, consisting of F₂, NF₃ , Xe, Kr, and Ar was optimized for the scaled laser conditions, resulting in 0.8-J output pulses at 486.8 nm, corresponding to an energy density of small-signal-gain measurements combined with kinetic modeling permitted the characteristics of the dependence of net gain on the electron-beam energy deposition and gas mixture composition, resulting in an improved understanding of XeF(C→A) laser operation     

Performance of an HF chain-reaction laser with high initiation efficiency

Output-pulse observations are presented for a tranverse electrically initiated, helium-diluted HF laser pumped by the H2+ F2chain reaction. Performance of this laser is studied over a wide range of the gas composition and for initial pressures between 0.1 and 0.5 atm. The gas mixture was stabilized by premixing O2, F2, and He and flowing this mixture into a cold trap (84 K) before mixing with H2. Optimum conversion of electrical-initiation energy into laser energy was found for a 240-torr mixture with a mole ratio 1 F2:0.23 H2:0.08 O2:12 He which, when initiated with a 25-kV, 333-pF discharge, gave a pulse energy of 0.150 J. This corresponds to a ratio of laser output energy to electrical input energy of 144 percent. After unnecessary losses are taken into account, this ratio becomes 160 percent.     

Electrical characteristics of an E-beam controlled KrF*discharge

Plasma electrical characteristics have been measured as a function ofe-beam current density (JB) and fluorine concentration for Ar, Kr, and F2gas mixtures in order to identify the stable operating regime of KrF* laser interest. The data were obtained from a 120 cm³active volumee-beam controlled discharge laser. The optimum F2concentration was found to be 0.17 percent at JB= 17.9 A/cm². This mixture also gave the best laser extraction efficiency and consequently produced the highest laser output energy. The dissociative electron attachment rate constant in the laser mixture was determined from the discharge voltage and current measurements.     

Simultaneous emission of the HF and N2 lines from aplasma cathode TEA laser

Simultaneous laser action from HF and N₂ is obtained, from a plasma cathode TEA laser, for the first time. The sliding discharge along the surface of a dielectric is used as a plasma cathode, for the main volumetric discharge. The laser operates at atmospheric pressure, with a gas mixture of SF₆:C₃H₈:N₂:He. For a typical flow rate ratio of 0.27:0.024:0.2:19.8 1 min^-1, it produces simultaneously 160 mJ HF and 0.6 mJ N₂ laser outputs at 0.43% and 1.4×10^-3% efficiencies respectively, at the moderate charging voltage of 28.5 kV. These output characteristics are obtained from a small active discharge volume and length of 10⁶ cm³ and 38 cm respectively. These values extend the performance, recently reported in the literature, of a sliding discharge HF/N₂ laser with corresponding simultaneous energy outputs of 12 mJ HF and 1.1 mJ N₂, to a higher energy output level, thus making the device suitable for a broader range of applications. This novel dual wavelength HF/N₂ laser system presented, can be particularly convenient for medical experiments, where the IR beam can be used for tissue ablation, while the UV beam can be used as the excitation source for fluorescence spectroscopic measurements, for the evaluation of the ablation process. Details are presented on the dependence of the laser performance parameters, such as output energy, discharge voltage and current and structure of the laser output pulses on the mixture composition and the circuit parameters     

Fabrication of carbon nanomaterials by atmospheric pressure microplasma

Atmospheric pressure microplasma was produced in a scanning electron microscope (SEM) chamber for synthesising carbon nanomaterials. The SEM observation is convenient for both adjusting the gap length and observing the electrode surface before and after experiments. After adjusting the gap length, the electrodes were housed in a small removable gas cell equipped in the SEM chamber and CH₄ discharge gas was introduced into the gas cell. It was found that the discharge was pulsated automatically because of slow discharge through a large ballast resistor and fast discharge through gas breakdown, even though a DC voltage was applied. The peak pulse current density was almost 60 kA/cm², the peak power density in the microplasma volume was approximately 555 MW/cm³ and the pulse width was 10 ns typically. Spherical and nanotube-like carbon nanomaterials were found on the cathode surface after microplasma discharge for 1? 5 s.With the discharge time increasing, the spherical substance changes into nanotube-like carbon nanomaterials.     

Diode-pumped LiF:F2+* color center lasertunable in 880-995-nm region at room temperature

Pulsed operation of a tunable LiF:F₂^+* color center laser has been obtained at room temperature under pumping by 680-nm fiber-coupled linear array laser diodes for the first time to the authors knowledge. The LiF:F₂^+* tunable laser operates in 880-995-nm region by use of an intracavity birefringent plate. Using a nonselective resonator the laser showed 3% pumping-to-lasing conversion efficiency. In the tunable narrow band operation the measured optical-to-optical conversion efficiency was 2%. The obtained result is expected to cause more widespread applications of diode-pumped LiF:F₂^+* laser and possibly its commercialization     

1.27μm atomic argon laser parameters in fission-fragment excitedHe/Ar and He/Ne/Ar gas mixtures

The authors examine the power efficiency of the fission-fragment-excited atomic argon laser operating on the 1.27-μm (3d'[3/2]₁-4'_p[3/2]₁) argon transition as a function of pump power, gas mixture, and pressure. The maximum measured power efficiency was 1.1±0.3% for a gas pressure of 1300 torr and a He/Ar ratio of 99.88/0.12. Neon addition to the He/Ar gas mixture increased both the energy deposited in the gas and the energy output without decreasing efficiency for a neon gas fraction of less than 0.5. Small-signal gain and saturation intensity are between 0.15-0.27%/cm and 25-200 W/cm² for pump rates of 7.5-30 W/cm ³ in He/Ar and He/Ne/Ar gas mixtures. The laser threshold as a function of total pressure and argon concentration is presented     

Generation of extreme ultraviolet radiation at 79 nm by sum frequency mixing

High brightness tunable coherent extreme ultraviolet (XUV) radiation at 79 nm with a peak power of ∼200 mW has been generated in H2gas by sum frequency mixing of two quanta from a high spectral brightness ArF* (193 nm) source with one quantum from a tunable dye laser (∼436 nm). Spectroscopic application of this radiation has been demonstrated by observation of a broad (∼160 cm^-1) autoionizing structure in Ar and narrow (∼2 cm^-1) autoionizing features in D2. An analysis is given which identifies the dominant molecular states involved in the nonlinear susceptibility of the medium (H2). The frequency independent tuning behavior of the 79 nm output power observed over ∼300 cm^-1is related to the molecular structure and response of the nonlinear medium in the intense optical field.     

Study of the XeCl laser pumped by a high-intensity electron beam

We present the results of a detailed experimental study of the XeCl laser pumped by a high-intensity electron beam. The laser system was optimized as an oscillator for mixtures of Xe and HCl with Ne, Ar, and Kr diluents. The peak intrinsic efficiency (laser energy out/electron-beam energy deposited) was near 4.5 percent for each of these diluents. Small-signal gain and background absorption were measured as a function of electron-beam deposition rate from 0.4 to 6 MW/ cm³. The ratio of small-signal gain to absorption was found to be constant over this range with a value of ∼5. Measurements of absorption in the presence of a large photon flux indicated that there was no appreciable saturable contribution to the absorption. Measurements of fluorescence from theBandCstates indicate that collisional mixing between these states is very rapid. The formation efficiencies of theBandCstates are estimated to be 0.15 and 0.05, respectively. A vibrational relaxation rate of between 1 and1.5 times 10^{-10}cm³. s^-1was determined. The effect of this finite relaxation rate is to reduce the energy available to the stimulated process by a factor of 0.67-0.75. Estimates of the XeCl* deactivation rates by HCl and electrons were also obtained. A value of1.7 times 10^{-9}cm³. s^-1was obtained for quenching by HCl, and a value ofsim 1 times 10^{-7}cm³. s^-1was estimated for electron deactivation.     

Unsaturated gain and output power of a 6328 Å He-Ne gas laser

The population inversion between the3S_{2}level and the2P_{4}level for He-Ne gaseous laser is calculated by solving rate equations in the four-level system in the steady state. Using this result, the unsaturated gain and the output power in laser oscillation as a function of discharge current are obtained for laser mediums with inhomogeneously broadened lines. The output power dependency on the excitation parameter is also obtained. The collision width and various transition rates in the transfer from helium to neon, spontaneous emission, induced emission and absorption, electron collision, and diffusion are appropriately chosen for the mixture of 1.0 torr helium and 0.1 torr neon in a 6-mm ID laser tube. The theoretical values of single-pass unsaturated gain for 65-cm plasma length and output power are 4.7 percent and 38 mW/cm², respectively, for a discharge current of 30 mA. The experimental values are 4.5 percent and 33 mW/cm², respectively, and almost coincide with the theoretical values. Furthermore, the saturation parameter is obtained theoretically as 490 mW/cm².     

Excitation mechanism and plasma parameters in pulsed argon-ion lasers

Pulsed argon-ion lasers show several interesting properties at high currents. To understand the inversion mechanism, the plasma parameters, electrical conductivity, electron temperature, and electron density were measured with the double-probe method for the pressure range from 15 to 50 mtorr in a 6-mm-bore tube. When the discharge current increases from 100 to 700 amperes at the optimum pressure for laser oscillation, these parameters increase from 250 to450Omega^{-1}cdotcm^-1, from8 times 10^{4}to10^{5}degK, and2 times 10^{14}to 10¹⁵cm^-3, respectively. At the maximum electron density, the percent of ionization appears to be in excess of 100 percent, as a result of the pinch effect and double ionization. It is certain that this ring discharge is at least ionized very strongly. In a 10-mm-bore tube, only the electron temperature and density were measured. The current dependence of the laser output power at high currents is interpreted with those results. Excitation mechanisms of high-current argon-ion lasers are discussed with experiments and theories for strongly ionized plasmas.     

千瓦级连续CO_2激光器电子温度的自动双探针测量系统

本文提出了用Z-80微型机控制的电子温度双探针自动测量系统,给出了数据处理的软件程序。在HGL-81型2kW级CO_2激光器上对放电等离子体进行了测量。在不同电流、不同气压、不同气体混合比例、不同位置测得的平均电子温度为(1.7～3.2)eV,平均电子浓度为(0.62～1.36)×10~(11)cm~(-3),平均比电场为2.0×10~(-16)V·cm~2。     

Fast axial flow CO2 laser excited by silent discharge

A fast axial flow CO₂ laser excited by silent discharge has been developed. With a new electrode system applied to the laser, homogeneous discharge of power density of up to 80 W/cm³ is obtained without applying any stabilization techniques on the discharge. An output laser power of 920 W in stable TEM₀₀ mode operation is attained with an efficiency of over 14%. Beam fluctuation common to fast axial flow lasers is suppressed by the combination of smooth gas flow and low CO₂ molar fraction     

Efficiency characterization of vacuum ultraviolet molecularfluorine (F2) laser (157 nm) excited by an intense electricdischarge

Detailed experimental results of a discharge-excited high-pressure F₂ laser are compared with a model prediction. Special emphasis is placed on the output performance of the discharge-pumped F ₂ laser at extremely high excitation rates (10~35 MW/cm³ ) by using high-pressure laser mixtures up to 8 atm. The kinetics model predicts fractional contributions of excited F₂ formation channels, relaxation channels, and absorption channels together with the formation and extraction efficiencies at the experimental conditions. Although the only experimental quantity compared with the model prediction is laser output energy, it is enough to obtain a better understanding of major F₂ laser kinetics and key issues for improving the efficiency     

Plasma chemistry of the closed-cycle 1 kHz transversely excitedatmospheric CO2 laser with an efficient catalytic CO2 regenerator

A high-power closed-cycle 1 kHz transversely excited atmospheric (TEA) CO₂ laser with an efficient catalytic CO₂ regenerator was used to investigate the variations of the average laser output power and the concentrations of the CO₂, CO, and O₂ molecules in the laser gas mixture with the operational performance of the CO₂ regenerator. It was experimentally shown that for the laser gas mixture of CO₂-N₂-He=15-15-70% and the output coupler reflectivity of 70%, η of 0.1 was required to maintain the laser output power greater than 90% of the initial laser output power of 570 W at an input energy density and a clearing ratio of 150 J/L and 3.0, respectively