A magnetically stabilized coaxial laser discharge

A new magnetic discharge stabilization technique for coaxial laser systems is described. The approach utilizes crosses electric and magnetic fields to create and maintain a large and rapidly rotating plasma volume which does not experience glow-to-arc transitions. Very high cw specific discharge power loadings have been achieved even without the benefit of external gas cooling or circulation.Performance is insensitive to gas composition and pressure such that high power coaxial discharges have been run in CO₂ laser gas mixtures up to several hundred torr. Stable cw discharges have also been obtained in mixtures containing several torr of SF₆.The technique appears to be readily scalable to give very large excited volumes in systems with comparatively small overall physical dimensions.     

Numerical simulation of gas flow in a magnetically stabilized coaxial laser discharge

The neutral gas flow profile within a magnetically stabilized coaxial laser gas discharge is analyzed by using a single fluid magnetogasdynamic model. Equations describing the rotational, radial and axial gas transport are solved by using an iterative alternating direction implicit method. Steady state rotational velocities of the order of 20 m/s are found.     

Spectroscopic diagnostics of the onset of discharge instabilities in a XeCl phototriggered laser

Study of the output power of a XeCl phototriggered laser at high energy loading has shown a multipulse operating mode. Above a critical value giving the maximum output energy, an increase of the applied electric field induces a dramatic decrease of the power emitted in the later peaks as well as the onset of a strong increase of the densities of various excited states, while such an increase is not observed for ionic states. Continuous-Wave (cw) laser-absorption spectroscopy is proved a very sensitive diagnostic tool to study the dynamics of these processes.On leave from Centre Técnico Aerospacial, S.J. Campos, Sao Paulo, Brazil     

Detailed vibrational population distributions in a CO2 laser discharge as measured with a tunable diode laser

A tunable diode laser (TDL) operating in the 2150–2350 cm^–1 wavenumber region is used to probe a conventional cw CO₂ laser discharge. Absorption lines in more than 25 different vibrational bands are observed, enabling us to determine absolute vibrational populations inall levels of concern to the dynamics of the 10 m CO₂ laser. Levels in thev ₃ mode of CO₂ as high as 00°9 are monitored, and it is found that anharmonic effects play a significant role in the populations of such levels. Thev ₁ andv ₂ mode populations are also investigated in detail, and it is found that these modes are strongly coupled and maintain a common vibrational temperature under all discharge conditions. The use of a TDL is shown to be a powerful technique for investigating the dynamics of infrared molecular lasers.This work was supported in part by the National Science and Engineering Research Council, Canada     

Space and time resolved discharge evolution of a large volume X-ray triggered XeCl laser system

The spatial distribution and the temporal development of the net gain have been measured in a ten liter active volume switchless discharge XeCl laser. The experimental results are compared with both zero-dimensional and two-dimensional kinetic code predictions. The comparison between the results of the kinetic codes and of some measurements relevant to the time-dependent discharge homogeneity allows a deeper insight into the influence of the streamer evolution on the discharge characteristics.ENEA StudentENEA Guest     

Numerical modeling of a XeCl laser excited by microwave discharge

12 , 169 (1987). Reasonably good agreements in the peak output power and laser efficiency have been achieved. Model calculations also predict that an efficiency as high as 2.7% can be obtained once the conditions of the above-mentioned experiments have been optimized. From the consideration that the skin depth effectively limits the absorption length of the microwave pumping and hence the excitable volume, it is concluded that high input power densities (>2 MW/cm³) and higher gas pressures (between 3 and 10 atm) are the preferable conditions to achieve higher efficiency. Preliminary calculations on CCl₄ containing XeCl gas mixtures show that improvement in laser efficiency by several folds may be achieved as a result of the higher intrinsic efficiency of excimer formation. Received: 23 September 1996 / Revised version: 25 March 1997     

Influence of cathode roughness on discharge homogeneity of a high-pulse repetition frequency long-pulse XeCl laser

Received: 17 October 1997/Revised version: 3 March 1998     

The role of halogen donors in discharge instability of rare-gas halide excimer lasers

Experimental results on striation instability in a self-sustained discharge-pumped XeCl laser are presented. The presence of HCl proves to be critical to the evolution of this particular mode of instability. The role of halogen donors in discharge instabilities of RGH lasers is discussed. That mixtures containing HCl will be susceptible to striation instability and those with F₂ or NF₃ will not is concluded.This work is based on experiments done when the author was at UCSD     

Pulsed inductive discharge CO2 laser

A pulsed inductive discharge CO₂ laser with a wavelength of 10.6 μm has been created for the first time. The excitation system of a cylindrical pulsed inductive discharge (pulsed inductively coupled plasma) in the gas mixture of CO₂:N₂:He was developed. The temporal and energy parameters of the laser radiation were investigated. The maximum inductive discharge CO₂ laser radiation energy of 104 mJ was achieved. An average power of 3.2 W was obtained at laser generation energy of 65 mJ and pulse repetition rate of 50 Hz. In the cross-section, the laser radiation had the ring shape with an external diameter of 34 mm and thickness of 4-5 mm. The measured divergence of laser radiation was 12 mrad.     

Small volume coaxial discharge as precision testbed for 0D-models of XeCl lasers

In order to check the predictions of 0D-models experimentally, a small coaxial discharge configuration for the generation of homogeneous high pressure glow discharges (diameter 11 mm, length 20 mm) in rare gas halogen excimer laser gas mixtures under accurately controlled conditions has been developed. It uses X-ray preionization and a special pulse-forming network (PFN) delivering fast rising (8 ns) single square pulses (U ₀=25 kV; I=300 A; =100 ns). Discharge current and voltage are measured precisely by a capacitive voltage divider and a shunt integrated into the discharge chamber. All circuit data needed for the model calculations have been evaluated. Interferometric and spectroscopic diagnostics of the bulk of the discharge and of the cathode sheath have been performed. First results for Ne/Xe/HCl mixtures are compared with model calculations.     

Linewidth studies on the Ar+ 476.5 nm and 480.6 nm lines excited in a helium-agron hollow cathode discharge

The spectral line shapes of the Ar⁺ 476.5 nm and 480.6 nm lines, excited in a He-Ar hollow cathode (HC) discharge, were measured using the Fabry-Perot technique. The collisional and Doppler linewidths were determined for the two lines. The collisional broadening constants are estimated to be (5±3) MHz/mbar and (6±3) MHz/mbar, respectively. The temperature obtained from the two Ar ion transitions was found to be 260 K higher than that expected for the rest of the gas mixture from earlier measurements. The possibility is discussed, that this excess temperature is caused by Ar ions partially created in the HC discharge by charge transfer collisions with He ₂ ⁺ molecules.     

Laser-assisted photoelectric optogalvanic analysis of thin films and surfaces using a hollow-cathode glow discharge

It is shown that substitution of the spectral line intensity with the photoelectric optogalvanic signal in the hollow-cathode glow discharge enhances the ability for layer-by-layer spectral analysis of surfaces and layers. In particular, this approach improves substantially the thin-film thickness measurements and analysis accuracy.     

Operation characteristics of the Au-II 690-nm laser transition in a segmented hollow-cathode discharge

Single-mode operation at the Au-II 690-nm transition was obtained in a segmented hollow-cathode discharge laser without the use of any additional frequency-selective device. The pressure of the helium buffer gas, which is responsible for the significant homogeneous broadening of the laser line, was varied between 10 and 20 mbar. The discharge was excited with rectangular current pulses (up to 3 A) six times exceeding the threshold value. The time dependence of the laser output during the 1-ms-long discharge pulses is explained on the basis of the temperature and pressure changes in the tube. The highest small-signal gain at optimal discharge conditions was 11%m⁻¹. Received: 1 July 1999 / Revised version: 4 November 1999 / Published online: 23 February 2000     

The spatial distribution of small signal gain in a segmented hollow cathode discharge laser

Received: 5 February 1997/Revised version: 30 April 1997     

Measurement of the gas temperature in a glow discharge by fluorescence spectroscopy

From the measurement of the distribution of sputtered iron atoms over the fine structure levels of the iron groundstate (a ⁵ D), the gas temperature of an argon glow discharge (p=1 Torr) has been derived under collision dominated conditions at distances larger than 30 mean free paths from the iron cathode.     

Analysis of new electrical signals in respect to quantification of radio frequency glow discharge emission spectrometry

Radio frequency glow discharge optical emission spectroscopy (RF-GD-OES) is routinely used for the chemical analysis of solid samples. For quantification two independent electrical signals of the discharge are required. These are provided in real time by the glow discharge source with integrated voltage and current sensors. The available time-dependent voltage and current must be reduced. For this purpose a plasma equivalent circuit is used. It is shown that the cathode voltage and active cathode current describe the sputtering and excitation well. Measuring standard reference materials at constant cathode voltage and cathode current results in linear calibration curves.     

Performance improvement of an x-ray preionized XeCl laser of very small discharge volume

Increasing the preionization electron density is found to be an effective method for improving the output performance of discharge-pumped excimer lasers at high gas pressures when the power-supply voltage becomes a limiting factor. In a small volume (2 cm³), x-ray preionized discharge, orders of magnitude improvement in XeCl laser power output (up to 400 kW) and pulse energy (up to 26 mJ) over previously reported results have been found possible using this method. Modifications to the low energy x-ray source and discharge system leading to these improvements are described. Various laser output characteristics are also presented and discussed.     

Argon laser with wall stabilized transverse discharge

Planar and cylindrical discharges for argon lasers are compared by plasmatheoretical calculations. The maximum laser output power available in the two arrangements is computed in dependence of various parameters neglecting saturation mechanisms. A transverse discharge arrangement confining the positive column by two parallel walls is described and experimental laser threshold values for the current and pressure are reported.     

Theoretical study of the feasibility of dual-band multiline operation of a TEA CO2 laser with intracavity fabry-perot etalons

It is shown that dual-band multiline operation of a TEA CO₂ laser can be conveniently achieved with the use of either one or two intracavity etalons of judiciously selected finesse and optical lengths.