M I de la Rosa

Measurement of Stark broadening and shift of singly ionized Ar lines

A very extensive compilation of Stark widths and shifts for more than 125 Ar II visible spectral lines is presented in this work. These atomic parameters have been measured in a pulsed discharge lamp by using different mixtures of pure argon or argon and helium. The electron density, which typically ranges from 0.2 to has been determined interferometrically and, in the case of pure argon plasmas, also spectroscopically from -Stark broadening. The Ar II excitation temperature (15 000-31 000 K) has been determined by Boltzmann-plot techniques from the intensity of Ar II lines. A detailed description of all the relevant points in this kind of measurement is given. Comparisons with most of the data published about this topic for Ar II are also included.

Measurement of Stark broadening and shift parameters of several Ar I lines

This work reports Stark shifts and widths of 15 Ar I lines measured in a pulsed arc. Plasma parameters, electron density and temperature, range in this experiment from 0.25 to and from 13 500 to 26 500 K, respectively. The former has been measured interferometrically at a single wavelength and spectroscopically from the -Stark broadening. The latter has been measured from the Boltzmann plot of Ar II lines and from the ratio of Ar II and Ar I line intensities. Comparisons with most of the data published to date about this topic in Ar I are also included.

Measurement of Stark broadening and shift of visible N II lines

This work reports information about Stark broadening and shift parameters of a very extensive collection of visible singly ionized nitrogen lines. All of them were measured in a linear discharge lamp from a mixture of nitrogen and helium. Electron density and temperature range in this experiment from 0.2 to 1.1 × 1023 m-3 and from 17 000 to 29 000 K, respectively. The first one has been simultaneously determined from two-wavelength interferometry and from the Stark broadening of He I 471.3 nm, the second from a Boltzmann plot of N II lines and from N II/N I intensity ratios. Dependences of these Stark parameters with temperature and electron density have been investigated and the final results have been compared with most of the previous experimental data as well as with two theoretical models. All relevant details relative to this experiment are given in the paper.

Electric field strengths in a hollow cathode measured by Doppler-free two-photon optogalvanic spectroscopy via Stark splitting of the 2S level of deuterium

We present, in this work, Doppler-free two-photon optogalvanic spectroscopy as a tool to measure the electric field strength in the cathode fall region of a hollow cathode discharge via the Stark splitting of the 2S level of atomic deuterium. The strong electric field strength (1 to 4 kV cm−1) present in the hollow cathode is determined for various discharge conditions (currents from 50 to 200 mA and pressures from 400 to 1350 Pa), which allows investigation of the corresponding variations of the cathode fall and its changes with discharge operation time.

Electric field measurements in a hollow cathode discharge by two-photon polarization spectroscopy of atomic deuterium

The local electric field strength (E-field) is an important parameter to be known in low pressure plasmas such as glow discharges, RF and microwave discharges, plasma boundaries in tokamaks etc. In this paper, we demonstrate, for the first time, the potential of two-photon polarization spectroscopy measuring the E-field in the cathode fall region of a hollow cathode discharge, via Doppler-free spectra of the Stark splitting of the 2S level of atomic deuterium. Electric field strength is determined in the range from 2 to 5?kV?cm?1. Compared with LIF, this method has several advantages: it is not affected by background radiation, it can be applied without limitation at elevated pressure and it allows simultaneous measurement of absolute local atomic ground state densities of hydrogen isotopes.

Absolute atomic hydrogen density distribution in a hollow cathode discharge by two-photon polarization spectroscopy

We report on quantitative measurements of ground-state atomic hydrogen densities in a stationary plasma far off thermodynamic equilibrium, generated in a hollow cathode discharge, by two-photon polarization spectroscopy via the 1S–2S transition. Absolute densities are obtained using a well established calibration method based on the non-resonant two-photon polarization signal of xenon gas at room temperature, which serves as the reference at the wavelength of the hydrogen transition. This study is dedicated to demonstrating the capability of two-photon polarization spectroscopy close to the detection limit. Therefore, it requires single-longitudinal mode UV-laser radiation provided by an advanced UV-laser spectrometer.

Calculation of the spatial resolution in two-photon absorption spectroscopy applied to plasma diagnosis

We report a detailed characterization of the spatial resolution provided by two-photon absorption spectroscopy suited for plasma diagnosis via the 1S-2S transition of atomic hydrogen for optogalvanic detection and laser induced fluorescence (LIF). A precise knowledge of the spatial resolution is crucial for a correct interpretation of measurements, if the plasma parameters to be analysed undergo strong spatial variations. The present study is based on a novel approach which provides a reliable and realistic determination of the spatial resolution. Measured irradiance distribution of laser beam waists in the overlap volume, provided by a high resolution UV camera, are employed to resolve coupled rate equations accounting for two-photon excitation, fluorescence decay and ionization. The resulting three-dimensional yield distributions reveal in detail the spatial resolution for optogalvanic and LIF detection and related saturation due to depletion. Two-photon absorption profiles broader than the Fourier transform-limited laser bandwidth are also incorporated in the calculations. The approach allows an accurate analysis of the spatial resolution present in recent and future measurements.

Development of pulsed UV lasers and their application in laser spectroscopy

The application of two-photon laser spectroscopy to plasma diagnostics requires tuneable UV-laser spectrometers providing: some mJ pulse energy at ns time scale with spectral quality close to Fourier Transform Limit, good pulse to pulse reproducibility and tuning linearity. We report about two different systems, a first laser specially optimized for the radiation at 243 nm, which is required for the 1S-2S two photon transition of atomic hydrogen, and a second one generating 205 nm suited for the transition 1S – 3S/3D.

Determination of electric field strength and kinetic temperature in the cathode fall region of a hollow cathode discharge

In this work, we demonstrate the high potential of two-photon excitation of the 1S -2S transition of atomic hydrogen followed by optogalvanic detection, for measuring under identical experimental conditions, the kinetic temperature and the electric field strength in the cathode sheath region of a hollow cathode discharge. The first obtained results for both parameters are discussed in this paper.

Characterization of hollow cathode fall field strength measured by Doppler-free two-photon optogalvanic spectroscopy via Stark splitting of the 2S level of hydrogen and deuterium

Doppler-free two-photon optogalvanic spectroscopy has been applied to measure the strong electric field strength and the cathode fall characteristics of hollow cathode discharges operated in hydrogen and deuterium via the Stark splitting of the 2S level of atomic hydrogen isotopes. In this paper we show similarities and differences in the tendencies of the cathode fall characteristics of hydrogen and deuterium in a wide range of identical discharge parameters.