Input Energy Density Research Articles

Continuous operation up to 3 kHz in a discharge-pumped XeCl excimer laser

Continuous operations at a high repetition rate up to 3 kHz for discharge-pumped XeCl excimer laser are presented. The dependence of the clearing ratio on laser-gas pressure and input energy densities is studied. It was found that suitable laser-gas pressures minimize the clearing ratio for various input-energy densities. It is also shown that few density disturbances in the discharge region are induced by gas heating in a discharge-pumped XeCl excimer laser with low input-energy density

Comparison of electrical discharge techniques for nonthermal plasma processing of NO in N/sub 2/

This paper presents a comparative assessment of three types of electrical discharge reactors: 1) pulsed corona, 2) dielectric-barrier discharge, and 3) dielectric-pellet bed reactor. The emphasis is on the efficiency for electron-impact dissociation of N/sub 2/(e+N/sub 2//spl rarr/e+N+N) and the subsequent chemical reduction of NO by nitrogen atoms (N+NO/spl rarr/N/sub 2/+O). By measuring the concentration of NO as a function of input energy density in dilute mixtures of NO in N/sub 2/, it is possible to determine the specific energy cost for the dissociation of N/sub 2/. Our experimental results show that the specific energy consumption (eV per NO molecule reduced) of different types of electrical discharge reactors are all similar. These results imply that, during radical production in electrical discharge reactors, the electric field experienced by the plasma is space-charge shielded to approximately the same value. The specific energy consumption for the dissociation of N/sub 2/ using electrical discharge processing is measured to be around 240 eV per nitrogen atom produced. In the NO-N/sub 2/ mixture, this corresponds to a specific energy consumption of around 240 eV per NO molecule reduced.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The energy conservation equation in the reflector mapping problem

We consider here an inverse problem in geometric optics consisting of finding a reflector surface that transforms a given input energy density pattern into a prespecified output energy pattern on the far field. We derive a single explicit relation expressing the ray tracing and energy conservation equations in terms of the polar radius of the reflector and its first and second derivatives. Conditions are given for existence of a solution to a boundary value problem describing a reflector system which transforms a nonaxially symmetric input energy density into a uniform output energy distribution.

Fracture mechanics of blunt cracks in a ductile steel

The propagation of blunt notches in stainless steel has been studied experimentally and analysed using generalized fracture mechanics (GFM), which takes account of inelastic and non-linear deformation. According to this theory, the critical apparent energy release rate, which is equivalent toJc, is given byJc=k1 (ɛ0)cW0c for an edge crack of lengthc in a thin sheet (plane stress), wherek1 (ɛ0) is a dimensionless function of strain, ɛ0, andW0c is the input energy density remote from the crack at the time of crack propagation. The validity of this equation was demonstrated for blunt cracks and the functionk1 (ɛ0) evaluated. The value ofJc was measured for blunt cracks of different lengths and tip diameters, and also for different crack extensions.Jc was found to be independent of crack length for the smallest tip radius, but became systematically length-dependent as the radius increased. However, the dependence ofJc on crack length, tip radius and crack extension can be expressed by a single empirical function, as is suggested by GFM. The propagation of cracks from blunt notches in ductile materials can, therefore, be handled by fracture mechanics methods.

The spatial scales of heterogeneities in the direct-current discharge stream

The results of a calculational-experimental investigation of spatial scale heterogeneities in a gas stream with direct-current discharge are presented. The numerical modeling was made within the framework of the Navier-Stokes equations with a distributed source of input energy density in a gas. The experimental study was conducted by the Talbot-interferometry method. The Shtrel number was used as the criterion of the optical homogeneity of the stream.

Plasma chemistry of the closed-cycle 1 kHz transversely excited atmospheric CO/sub 2/ laser with an efficient catalytic CO/sub 2/ regenerator

A high-power closed-cycle 1 kHz transversely excited atmospheric (TEA) CO/sub 2/ laser with an efficient catalytic CO/sub 2/ regenerator was used to investigate the variations of the average laser output power and the concentrations of the CO/sub 2/, CO, and O/sub 2/ molecules in the laser gas mixture with the operational performance of the CO/sub 2/ regenerator. It was experimentally shown that for the laser gas mixture of CO/sub 2/-N/sub 2/-He=15-15-70% and the output coupler reflectivity of 70%, eta 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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Catalytic control requirements for the stable operation of the closed-cycle, transversely excited atmospheric CO2 laser

Using a comprehensive theoretical CO2 laser model, we calculated the amount of the catalytic conversion from CO to CO2, which is required for the stable and long-life operation of the closed-cycle, transversely excited atmospheric CO2 laser. The amount of the catalytic conversion was evaluated by the fractional conversion (η) defined as η=([CO]in−[CO]out)/[CO]in, where [CO]in and [CO]out are the CO molecules number density at the entrance and exit of the CO2 regenerator in the laser chamber, respectively. For the laser gas mixture of CO2/N2/He=15/15/70(%) and the output coupler reflectivity of 80%, an η of the CO2 regenerator greater than 0.22 is theoretically required to maintain the 95% level of the initial laser output energy at an input energy density and a laser gas clearing ratio CR of 176.1 J/ℓ and 2.0, respectively.

Development of corona-preionized TEA-CO2 laser with HFCD circuit recycling residual energy.

In a corona-preionized TEA-CO2 laser, high-frequency corona discharge (HFCD) was superposed on the main discharge by utilizing a new circuit called as SC-HFCD (Self-Charged HFCD) circuit. In the SC-HFCD circuit, a part of residual electric energy, which is usually lost by heating of resistive components in a discharge circuit, is recycled as an electrical source for the HFCD in the next laser operation. Therefore it is possible to increase the total efficiency because the energy for the HFCD is saved. The maximum laser output energy of 17.5J/l was obtained with the SC-HFCD circuit at an input energy density of 250J/l, while an arc-free condition was maintained for input energy densities up to 230J/l. The performance of the SC-HFCD circuit was also explained theoretically.

Improvement of a Corona-Preionized TEA-CO2 Laser by Means of High-Frequency Corona Discharge

It is reported that the input and output energy density of about 220 J/1 and 14 J/1, respectively, are obtained in a corona-preionized TEA-CO2 laser with the superposition of the high-frequency corona discharge (HFCD) on the main discharge. There is an optimum delay time between the initiation of the HFCD current and the main discharge. Also, it is necessary for the HFCD current to have a high peak value, a short-period oscillation and a duration of more than 1 µs to increase the laser output and to suppress the glow-to-arc transition. These conditions for the HFCD current are satisfied by the reduction of both resistance and inductance in the HFCD circuit.

A semiconductor preionised DF laser

Semiconductor preionisation is used to stabilise the discharge in a SF6:D2 gas mixture. This results in good discharge stability in the electronegative gas mix and allows high input energy density resulting in good shot-shot stability, high output energy density and peak power from a DF laser.

Characteristics of a high-pressure CO2laser with ultraviolet preionization by surface channel discharges

A surface channel discharge was used as the source of ultraviolet radiation for pulse-periodic photoionization of CO2 laser mixtures. This source was sufficiently powerful to ensure a volume discharge at pressures of ~5 atm necessary for continuous tuning of the emission frequency. Experiments on the use of this source in a laser showed that it could be used at pressures up to 3 atm and in this range the input energy density was 500 J/liter, the output energy density was ~30 J/liter, and the actual output energy in the form of laser radiation was 2.3 J.

Measurements of x-ray dose required for multiatmospheric pressure CO2 laser discharge

We have investigated the preionization characteristics of x ray for a transversely excited, multiatmospheric pressure CO2 laser amplifier with an active volume as large as 225 cm3. The x-ray dose required for uniform avalanche discharge is measured as a function of pressure up to 10 atm. The dependence of the input energy density of the main discharge on the x-ray dose is also investigated.

Low-pressure flashlamps: influence of the wall ablation phenomena on their output characteristic

When operating with linear low-pressure flashlamps (0.1–20 Torr) two different linear zones of the Eout/Ein characteristics are described: high-energy density zone corresponds with a wall-ablation regime having a strong influence from the material extracted from the walls; low-energy density zone corresponds with an isolated normal discharge regime. Spectroscopic measurements also demonstrate this behavior. The input energy density needed for the regime transition is constant when varying tube geometry. Pyrex and quartz tubes with 10-μsec pulses; the value of Etransition was ∼38 J/cm3 at 5-Torr air pressure.

Electric-discharge XeCl laser with high spatial homogeneity and energy density of output radiation

A study was made of an electric-discharge XeCl excimer laser (308 nm) having an active volume of ~ 120 cm3 and a highly homogeneous discharge, with a beam of 2 × 2 cm cross section. An investigation was made of the energy and temporal characteristics of the laser obtained using different excitation systems. For a radiation energy of 0.3 J, a specific output energy density of 2.6 J/liter was obtained. A good spatial homogeneity of the emitted radiation combined with a high output radiation energy density was achieved by selecting the gas mixture composition and by raising the input energy density.

Generalized fracture mechanics of ductile steels

The generalized fracture mechanics approach is applied to two ductile steels, namely mild steel and 18/8 stainless steel in plane stress. The theory defines a fracture parameter\(\mathcal{T}\), which is a truly plastic analogue of theJ contour integral and, for an edge crack specimen, is given by $$\mathcal{T} = k_1 ( \in _0 )cW_{0_c } $$ wherek1 is an explicit function,c is the crack length ande0, W0c are respectively the strain and input energy density at fracture, remote from the crack. The functionk1(eo) is derived experimentally and the constancy of\(\mathcal{T}\) with respect to crack length and applied load is demonstrated. The variation of\(\mathcal{T}\) with crack extension during slow growth is investigated, as is the rate dependence of\(\mathcal{T}\) in mild steel.

Stabilized TEA CO2laser with double photopreionization and low-ionization-potential additives

An experimental investigation was made of the influence of various low-ionization-potential additives on the energy and electrical characteristics of a TEA CO2 laser stabilized by the double preionization method. In the absence of additives the maximum input energy density was 900 J/liter; in the presence of triethylamine and diethylaniline at a pressure of 0.5 Torr the density increased to 1250 J/liter. When the vapor pressure of the additives was too high, the output energy of the laser decreased; the optimal vapor pressure of all the additives in our experiments was < 1 Torr at the atmospheric pressure of the laser gas mixture.

Pulsed TEA CO2laser with an input energy density of 1.1 kJ/liter stabilized by a double preliminary discharge

A simple and reliable laboratory model of a TEA CO2 laser with photopreionization by a double discharge was constructed. The current-voltage characteristics and the influence of the addition of easily ionized mixtures on the discharge stability were investigated. The maximum input energy achieved was 1.1 kJ/liter; the corresponding laser output energy was 60 J/liter.

5207. Faraday cup analysis of ion beams produced by a dense plasma focus: G Gerdin et al,J Appl Phys,52 (5), 1981, 3269–3275

The role of the nitrogen ion beam generated with a small energy plasma focus (PF) device in the thermal processing of an austenitic stainless steel substrate is discussed. A numerical solution of the heat equation which takes into account the temperature variations of the thermal coefficients of the material is presented. By using several characteristics of the beam determined in previous works, it is found that the energy content of the beam is not enough to promote a strong heating of the outer layers of the substrate, which is required to explain the introduction of foreign particles to depths well beyond the ion range in the material, and also the martensitic transformation of steel up to a depth of ≈0.6 μm found in this work. The surface treatment is thus attributed to a plasma bubble generated by the disruption of the plasma column, and some evidence of its presence is obtained by employing a Faraday cup (FC). When the numerical model is used with an input energy density corresponding to the experimental value, and with a delivery time equal to the temporal width of the bubble, the evolution of the temperature profiles along the substrate depth shows a melting front reaching the proper depth to explain the penetration of Ti and N atoms found in a previous work, and the martensitic transformation depth presented in this work.

Relative influence of hydrogen/deuterium donors and driving circuit parameters on the performance of a uv preionized pulsed HF/DF laser

The influence of the preionizer and initiating discharge circuit parameters on the performance of a UV preionized pulsed HF/DF chemical laser with relatively low active volume (about 20 cm3) has been investigated. The laser has been operated with gas mixtures of SF6 and H2, C2H6, and D2 at pressures ?90 Torr, giving laser output energies up to ∼70 mJ with a maximum efficiency of about 2.2%. We observed that the insertion of a peaking capacitor bank across the main discharge gap strongly affected the laser output characteristics. The laser output energy was seen to vary with the capacitance of the peaking capacitor bank, whose influence is a function of the SF6 partner in the laser mixture, the gas pressure, and the input energy density into the discharge.

High pressure infrared xenon laser excited by a UV preionized discharge

Laser action from neutral Xe transitions has been achieved in an Ar–Xe mixture at 1 atm and in a He–Xe, He–Ar–Xe mixture at 2.5 atm excited by a UV preionized short discharge (Δt?50 ns). In the best mixture, He–Ar–Xe (100–60–1), an overall conversion efficiency of 0.2% was obtained with a 10-mJ output. These nonoptimized results may be improved by decreasing the input energy density and increasing the pressure.