Electron-beam Sustained Discharge Research Articles

Dynamics of frequency-selective operation of a CO laser tunable in a wide spectral range

This paper presents a computational/theoretical analysis of the generation of a single pulse by a frequency-selective electron-beam sustained discharge CO laser. The calculations have been performed using a theoretical model in which the entire set of VV exchange processes involving CO molecules at high vibrational levels is taken into full account. We present calculated pulse shapes for a wide range of transitions, including transitions between high vibrational levels, and examine the possibility of raising the laser output intensity by optimising the density and composition of the gain medium.

Diagnostics of Low Temperature Plasma by CO Laser Radiation (5.0-7.5 μm)

A review of the work conducted in Gas Lasers Laboratory of P.N. Lebedev Physical Institute of the Russian Academy of Sciences and devoted to a research of the diagnostic of dynamics of small-signal gain, temperature and population of vibrational levels in the CO-containing gas mixtures excited by pulsed electron-beam sustained discharge is presented. With the help of laser probing techniques the nonlinear Zeeman splitting of the NO lines in a strong magnetic field was also investigated. The studies of gain of the train of nanosecond pulses allowed us to estimate the intensity of the gain saturation of the active medium of the pulsed electron-beam sustained discharge CO laser.

Novel mode-locked carbon monoxide laser system achieves high accuracy

Extending the emission range of gas lasers is an attractive proposition, for example, in laser spectroscopy, atmosphere sensing, laser media diagnostics, initiating chemical reactions, and separating elemental isotopes. In this context, carbon monoxide (CO) lasers offer several advantages over other sources of IR radiation, including control of output energy and pulse duration over a wide dynamic range. Moreover, they ensure high average power in repetitively pulsed modes. An electric discharge CO laser can operate on every spectral line from among a few hundred in both fundamental ( 4.7–8.2 m)1 and firstovertone ( 2.5–4.2 m) spectral bands.2–4 In addition, parametric frequency conversion (i.e., frequency doubling, or sum or difference frequency generation) of CO laser radiation using a single nonlinear crystal can cover both midand far-IR spectral ranges. However, to achieve high-frequency conversion efficiency, CO laser radiation must have high peak power. The first mode-locked (i.e., pulsing) laser was reported decades ago. But it had a peak power of only a few kilowatts because it operated at room temperature. No efforts have been made since then to obtain substantially higher power. We have developed a cryogenically cooled, electron-beamsustained-discharge (EBSD) mode-locked CO laser that produces a train of 5–15ns full width at half-maximum spikes with a pulse repetition rate of 10MHz in the mid-IR range of 5 m.5 We obtained maximum output power of up to 120kW for a multiline mode and 70kW for a single-line mode of operation. As suggested elsewhere,6 such radiation could be used to pump an optical parametric amplifier for stochastic cooling in a relativistic heavy-ion collider (see Figure 1). Figure 1. Imaginary layout of the optical stochastic cooling system for the relativistic heavy-ion collider (Brookhaven National Laboratory, US). The storage ring measures 4km. CO: Carbon monoxide. : Wavelength. OPA: Oscillator-power amplifier. : Wavelength.

CO激光在非线性晶体ZnGeP2和GaSe中的混频效应

The CO laser frequency mixing in high-quality ZnGeP2 and GaSe crystals is studied to obtain the 2.15-1 500 μm coherent sources.Secondary Harmonic Generation(SHG),sum-and difference frequency generations are considered as a method for the CO laser frequency mixing and the mode-locking as an efficient way to improve the mixing efficiency.Results show that the internal SHG efficiency of Q-switched multiline CO laser radiation has exceeded by 0.3% for GaSe crystal and has reached by 1.1 % for ZnGeP2 crystal.When the SHG is in ZnGeP2,the internal efficiency of electron beam sustained discharge frequency-tunable mode-locking CO laser is up to 12.5 %.Simultaneous SHG and sum frequency generation show the same output spectrum.It is shown by modeling that the sum and difference frequency generations of neighboring lines of both fundamental and first overtone bands can allow one to get the oscillation,respectively,at 4.0-5.0 μm and 100-≥1 200 μm(THz).In conclusions,the frequency mixing of mode-locked CO laser emission lines in ZnGeP2 crystals allows some one to design 2.15-≥1 500 μm coherent sources with the power frequency conversion efficiency up to or over 12.5%.

Optimization of electron-beam sustained discharge laser electrodes system

One of the basic problems at creation of powerful electron-beam sustained discharge lasers is achievement of the greatest possible intensity of an electric field in the charge volume limited to the aperture of the resonator and uniformity of power pumping on this volume. In our opinion known types of electrodes, for example,, etc. are not optimum, and the recommendations hallmarking a ratio of electrodes width to interelectrodes distance as 4:1, are a little bit overestimated.It is shown, what even at high uniformity of an electric field in the interelectrodes volume covered with the optical resonator, heterogeneity of pumping power density in cross section of the charge can reach 100%.

Electron-beam sustained CO2 laser operating on CO2 : N2 : H2O mix

Users of high power CO2 lasers may be interested in finding a substitute for expensive He which would provide sufficient efficiency and specific power of laser radiation. In the present work, operating modes of the electron-beam sustained discharge CO2 pulse-periodic laser operating on CO2:N2:H2O mixes were investigated. The research has revealed that at equal energies of radiations the efficiency for CO2:N2:H2O mixes are approximately 25% lower than those for CO2:N2:He mixes. The decrease in efficiency is compensated for by an increase in electric strength of the mixes containing H2O, both in pulse and in pulse-periodic modes.

Simulation of electron-beam sustained discharge laser

The complex program simulating processes in the electron-beam sustained discharge laser (EBSL) is created. It simultaneously models processes of electron beams spread in electron accelerator, elements of a design and the flash chamber under influence electric and magnetic fields; processes of formation of spatial distribution of an electric field and a secondary electrons current in the flash chamber. The self-consistent interaction of accelerated electron beams with spatial distribution of an electric field in the flash chamber, generated by the impressed voltage and conductivity of the laser gas mix generated, in turn, by accelerated electron beams is taken into account. The program is realized on a personal computer and allows quickly changing parameters and elements properties of design EBSL. Spatial characteristics of the discharge are determined. Comparison with earlier published and experimental data has shown good conformity. One of the purposes of the given program is to change onedimensional thinking on spatial at designing complex electro physical devices.

Pulsed electron-beam sustained discharge CO laser on oxygen-containing gas mixtures

It is shown that the addition of molecular oxygen to the working mixture of a pulsed electron-beam sustained-discharge (EBSD) laser CO amplifier leads to the increase in the small-signal gain (SSG) at the fundamental vibrational v+1→v transitions in a CO molecule for v=6–13, which is explained by the increase in the population of vibrational levels. In this case, the temporal parameters of the dynamics decrease at all probed transitions. Variations observed in the SSG dynamics are explained by analysing the kinetic processes of vibrational—vibrational exchange between molecules. The study of lasing parameters of a pulsed CO laser showed that the threshold energy input decreased with increasing the oxygen content in the working mixture. It is found that the CO laser efficiency at fundamental transitions increases with the addition of oxygen, the maximum efficiency being achieved at lower energy inputs. It is shown that the pulsed EBSD CO laser can operate on the air working mixture both at the fundamental transitions and the first vibrational overtone transitions v+2→v.

Multiline laser probing of CO:He, CO:N2, and CO:O2 active media in a wide-aperture pulsed amplifier

Multiline laser probing was applied for the diagnostics of the active medium of a wide-aperture carbon monoxide laser amplifier. The temporal behavior of the small-signal gain in the active medium of a pulsed electron-beam sustained discharge CO laser amplifier was studied with a specially designed probe CO laser in a wide range of ro-vibrational spectral lines (from V = 5 up to V = 31). The results were analyzed in order to reconstruct the temporal behavior of gas temperature and vibrational populations in CO-containing gas mixtures, CO:He and CO:N2, and oxygen-rich CO: O2 mixtures.

Pulsed electron-beam-sustained discharge in oxygen-containing gas mixtures: electrical characteristics, spectroscopy,and singlet oxygen yield

The electrical and spectroscopic characteristics of electron-beam-sustained discharge (EBSD) in oxygen and oxygen-containing gas mixtures are studied experimentally under gas pressures up to 100 Torr in a large excitation volume (∼18 L). It is shown that the EBSD in pure oxygen and its mixtures with inert gases is unstable and is characterised by a small specific energy contribution. The addition of small amounts (∼1%-10%) of carbon monoxide or hydrogen to oxygen or its mixtures with inert gases considerably improves the stability of the discharge, while the specific energy contribution W increases by more then an order of magnitude, achieving ∼6.5 kJ L-1 atm-1 per molecular component of the gas mixture. A part of the energy supplied to the EBSD is spent to excite vibrational levels of molecular additives. This was demonstrated experimentally by the initiation of a CO laser based on the O2 : Ar : CO = 1 : 1 : 0.1 mixture. Experimental results on spectroscopy of the excited electronic states O2(a1Δg) and O2(b1Σg+), of oxygen formed in the EBSD are presented. A technique was worked out for measuring the concentration of singlet oxygen in the O2(a1Δg) state in the afterglow of the pulsed EBSD by comparing with the radiation intensity of singlet oxygen of a given concentration produced in a chemical generator. Preliminary measurements of the singlet-oxygen yield in the EBSD show that its value ∼3% for W ∼ 1.0 kJ L-1 atm-1 is in agreement with the theoretical estimate. Theoretical calculations performed for W ∼ 6.5 kJ L-1 atm-1 at a fixed temperature show that the singlet-oxygen yield may be ∼20%, which is higher than the value required to achieve the lasing threshold in an oxygen—iodine laser at room temperature.

Non-self-sustained electric discharge in oxygen gas mixtures: singlet delta oxygen production

The possibility of obtaining a high specific input energy in an electron-beam sustained discharge ignited in oxygen gas mixtures O2 : Ar : CO (or H2) at the total gas pressures of 10–100 Torr was experimentally demonstrated. The specific input energy per molecular component exceeded ∼6 kJ l−1 atm−1 (150 kJ mol−1) as a small amount of carbon monoxide was added into a gas mixture of oxygen and argon. It was theoretically demonstrated that one might expect to obtain a singlet delta oxygen yield of 25% exceeding its threshold value needed for an oxygen–iodine laser operation at room temperature, when maintaining a non-self-sustained discharge in oxygen gas mixtures with molecular additives CO, H2 or D2. The efficiency of singlet delta oxygen production can be as high as 40%.

Negative differential conductivity of electrons in electron-beam sustained discharge in pure xenon

The mechanism of negative differential conductivity (NDC) in an electron-beam sustained gas discharge of pure Xe is investigated by modeling. The drift velocity of electrons in Xe has been calculated using a self-consistent kinetic model. Model calculations involves the self-consistent solution of the Boltzmann equation for electron energy distribution function in the two-term approximation and a complete set of rate equations for the excited and ionic species in the discharge plasma. It is shown that the main factor responsible for the observation of the NDC effect is Coulomb interaction between electrons. Regions in experimentally achievable parameter space where NDC can be observed are determined.

Synthesis and properties of CeN thin films deposited by arc ion plating

Cerium nitride films were deposited by ion plating in an electron-beam sustained Ce arc discharge in a nitrogen atmosphere. The crystal structure was strongly affected by the arc discharge current and the substrate temperature. The lattice spacing of CeN film is 0.5020 nm with a density of 7.82 g cm−3. This film showed a paramagnetic property at 10 K in a magnetic field of 20 kOe. The Knoop hardness for CeN film is over 1600. The electrical resistivity was 4.6 × 10−4 Ωcm with p-type conductivity. The carrier concentration of the CeN film increased after exposure to the air, which suggested that the valence of Ce in CeN is probably 4+.

Long pulse 250 keV electron gun for high-pressure gas lasers

The design and performance of a secondary emission electron gun with a wire ionized plasma as an ion source is discussed. An electron beam current density of up to 100 mA/cm2 is obtained over an area of 55×5 cm2 at a cathode voltage of 250 kV in pulses with a duration of about 20 μs. The current distribution over the beam area is uniform to better than 25%. The achieved combination of pulse duration, beam current, and electron energy is attractive to excite high-pressure gas laser media. Preliminary results with the utilization of the gun in an electron beam sustained discharge excited atomic Xe laser show an output energy of 1 J/ℓ at a wavelength of λ=1.73 μm.

Saturation studies of the E-beam sustained discharge atomic xenon laser

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/cm/sup 2/ 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/sup -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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Generation of, and tolerance to, dissociation products in an electron-beam sustained carbon dioxide laser

The extent of carbon dioxide dissociation in an electron-beam sustained CO2 laser discharge was found to be proportional only to the total charge passed and the CO2 partial pressure; the rate of oxygen production was found to be 150 mu mol C-1 referred to pure carbon dioxide. The dissociation occurs in the cathode sheath. The effects of dissociation products on small-signal gain, discharge impedance, and on the glow-arc transition were studied. It was found that only oxygen had any influence and that this was confined mostly to the increase of impedance caused by attachment. An analysis of the implications of impedance matching to discharge stability is presented.

Characteristics of the high-pressure Ar-Xe laser pumped by an electron beam and an electron-beam sustained discharge

Mechanisms of the line competition observed among the 1.73-, 2.03-, and 2.65- mu m lines are interpreted based on the gain and saturation data along with some known kinetics. The energy distribution among the lines is also investigated as a function of various operating parameters. An enhancement factor of approximately 10 was readily obtained for both electrical input energy and laser output energy in the e-beam sustained discharged. However, there is a tradeoff between enhancement factors and laser output energy due to a degradation of the laser output observed for discharge power enhancements greater than 5. The maximum output energy obtained was 4 J/l, with an intrinsic efficiency of approximately 3%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Discharge instabilities initiated by nonuniform laser extraction in electron-beam sustained discharge KrF lasers

The photon energy of KrF lasers (λ=248 nm) is sufficiently large to photodetach electrons from the halogen negative ion (F−) and to photoionize excited states of krypton. In electron-beam (e-beam) sustained discharge KrF lasers, the contribution of photogenerated electrons to the total rate of ionization can be large enough to significantly perturb the conductivity of the plasma. If laser oscillation is spatially nonuniform, the photoelectron contribution to the conductivity deforms the local electric field. This condition can ultimately lead to a local discharge ionization instability and an arclike termination of the discharge. In this paper, the effect of nonuniform optical extraction on the discharge stability of an e-beam sustained discharge KrF laser will be studied with results from a two-dimensional time-dependent discharge kinetics and laser extraction model. Examples of stable and unstable configurations will be presented. The time at which the arclike ionization instability terminates the discharge correlates with the time that multistep ionization becomes an appreciable fraction of the total rate of ionization . A criterion for discharge stability is proposed; gradients in conductivity caused by photogenerated electrons must be either perpendicular or parallel to the bulk electric field.

Ion-ion recombination in mixtures of methane and sulphur hexafluoride

The authors have measured the recombination rate for positive and negative ions in sulphur hexafluoride and in mixtures of methane and sulphur hexafluoride in an electron beam sustained discharge. Measurements were made as a function of gas composition, gas pressure in the range 100 to 600 Torr, and reduced electric field strength in the range 12 to 150 Td. When plotted as a function of an effective ion temperature, defined by the drift velocities of the ions in the applied electric field, the rates in each of the gas mixtures follow the same Teff-1.6 power law. From comparisons with theories appropriate to the recombination of positive ions with electrons it is suggested that the index of the power law might indicate that the recombination process follows an indirect path, with the approaching ions being initially trapped in stable orbits before final stabilisation of the collision.

Soft Vacuum, Pulsed Electron Beam Processing of Polyimides

ABSTRACTWe report on the successful patterning of polyamic acid over wide areas using 28 kV pulsed electron beams produced in 30 mTorr air. The pattern degradation during the 350°C, 1/2 hr, imidizing thermal cure is prevented by pulsed, flood electron beam hardening of the developed polyamic acid patterns using the same soft vacuum, pulsed electron beam apparatus. It is also shown that a CW, low voltage, 1 to 3 kV electron beam sustained oxygen discharge can be used to completely strip the hardened, imidized material which is difficult to remove by wet methods. We also present, dose versus thickness remaining characteristics as a function of electron source to substrate distance and some examples of polyimide patterning.