K Grützmacher

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.

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.

Characterization of a hydrogen hollow cathode plasma by two-photon polarization spectroscopy

We applied for the first time two-photon polarization spectroscopy to study in detail a hydrogen plasma far off thermodynamic equilibrium generated in a hollow cathode discharge. The aim of the investigation is to measure important plasma parameters like atomic ground state densities, electron densities, local electric field strength and kinetic temperatures. This is possible, because an advanced UV laser spectrometer is providing sufficient power at 243 nm in a narrow spectral bandwidth, that allows to resolve the hyperfine structure of the 1S-2S hydrogen transition.

Influence of the cathode material in the cathode fall characteristics of a hydrogen hollow cathode glow-discharge

In this work, we present Doppler free two photon optogalvanic measurements to determine the local electric field strength (E-field) in the cathode fall region of a hollow cathode discharge, operated in pure hydrogen, via the Stark splitting of the 2S level of hydrogen. The main aim of this article is the comparison of the measurements made with different cathode materials, stainless steel, and tungsten; both of them are widely used in the low-pressure discharges. Sputtering of stainless steel is the principle cause of the differences observed for the E-field variation, and the differences are analyzed in the frame of the sputtered material in a wide range of discharge conditions. Complementary images of the discharge luminosity allow for the conclusion; the cathode dark zone corresponds in good approximation to the cathode fall length.In this work, we present Doppler free two photon optogalvanic measurements to determine the local electric field strength (E-field) in the cathode fall region of a hollow cathode discharge, operated in pure hydrogen, via the Stark splitting of the 2S level of hydrogen. The main aim of this article is the comparison of the measurements made with different cathode materials, stainless steel, and tungsten; both of them are widely used in the low-pressure discharges. Sputtering of stainless steel is the principle cause of the differences observed for the E-field variation, and the differences are analyzed in the frame of the sputtered material in a wide range of discharge conditions. Complementary images of the discharge luminosity allow for the conclusion; the cathode dark zone corresponds in good approximation to the cathode fall length.

Optogalvanic spectroscopy measurements of the electric field strength in a hydrogen glow discharge

A high-resolution spectroscopy method is used in order to measure the electric field distribution in a hollow cathode glow discharge in hydrogen.

Analysis of the measured 1S-2S Stark spectra of hydrogen isotopes used for E-field strength determination in a hollow cathode discharge

This paper is dedicated to analyse in detail the Stark splitting spectra of the 1S – 2S transition of hydrogen isotopes, used to determine the local electric field strength in the cathode fall of a hollow cathode discharge, by measuring the Doppler free two-photon absorption via optogalvanic detection. The measured irradiance distribution in the overlap volume of the two laser beams is used to integrate the rate equations, which give the ion yield distribution with high spatial resolution. Inserting the local ion yield in the local electric field strength of the cathode fall allows reconstructing and analysing the Stark splitting spectra.

Measurements of two-photon absorption cross-section of Xe for laser spectroscopic techniques calibration

Two-photon transition cross section for one xenon transition (5p6 1S0-5p56p[1/2]0) will be measured with very low uncertainty by two-photon polarization spectroscopy. The method, which is explained in this paper, is based on a comparison of direct measurements of the two-photon absorption in xenon gas at two closed wavelengths (resonant and no resonant).