Excitation and ionization of atoms out of the 4 energy levels of the excited np 5 (n + 1)s configuration of rare gases play an important role in many low temperature rare-gas plasmas. We compare two optical methods for measuring the number densities of atoms in these excited levels in an inductively coupled plasma under a variety of operating conditions (600 W, 1-25 mTorr). The first method is a standard white light absorption technique, whereas the second method exploits changes in the effective branching fractions of np 5 (n + 1)p → np 5 (n + 1)s emissions brought about by radiation trapping of atoms in np 5 (n + 1)s levels. The branching fraction method was found to produce results that agree well with the direct white light absorption method for both argon and neon plasmas using little more than a low-resolution spectrum of the plasma glow.

Optical modeling of emissions from low-temperature plasmas provides a non-invasive technique to measure the electron energy distribution function (EEDF) of the plasma. While many models assume the EEDF has a Maxwell-Boltzmann distribution, the EEDFs of numerous plasma systems deviate significantly from the Maxwellian form. In this paper, we present an optical emission model for the Ar(3p 5 4p → 3p 5 4s) emission array which is capable of capturing details of non-Maxwellian distributions. Our model combines previously measured electron-impact excitation cross sections with Ar(3p 5 4s) number density measurements and emission spectra. The model also includes corrections for radiation trapping of the Ar(3p 5 4p → 3p 5 4s) emission lines. Results obtained with this optical technique are compared with corresponding Langmuir probe measurements of the EEDF for Ar and Ar/N 2 inductively coupled plasma systems operating under a wide variety of source conditions (1-25 mTorr, 20-1000 W, %N 2 admixture). Both the optical emission method and probe measurements indicate the EEDF shapes are Maxwellian for low electron energies, but with depleted high energy tails.

We explore the feasibility of using the ratio of two argon emission line intensities at 420.1 and 419.8 nm to measure the effective electron temperature in argon-containing plasmas. Experimental measurements in numerous plasma sources reveal the ratio varies from a value of approximately 1 at high electron temperatures, to a value near 4 at low electron temperatures. This variation is understood in terms of the magnitudes of the electron excitation cross sections into the upper energy levels of the two transitions. At high electron temperatures, the upper levels of the two emission lines, the J = 3 3p9 level for the 420.1 nm line and the J = 0 3p5 level for the 419.8 nm line, are both primarily populated by excitation from the ground state and have similar optical emission cross sections. At low electron temperatures, excitation is dominated by excitation from the metastable levels which have very different cross sections into the two levels. Temperatures obtained with this line pair ratio in an inductively coupled plasma are found to be consistent with values obtained from a Langmuir probe as well as an analysis of the entire set of 2p x  → 1s y emission lines (665–1150 nm) under a wide variety of plasma conditions.

Phase-resolved optical emission spectroscopy measurements in argon and neon inductively coupled plasmas (ICPs) have revealed a surplus of high-energy electrons in neon-containing plasmas. Differences between results of emission model analyses using neon and argon lines (as well as probe measurements) also indicate a high-energy enhancement in neon-containing plasmas. The abundance of these extra high-energy electrons is correlated with the sheath thickness near the rf antenna and can be reduced by either adding a Faraday shield (external shielding) or increasing the plasma density. A comparison of modelled and experimental values of the 13.56 MHz time modulation of select neon emission lines strongly suggests plasma series resonance heating adjacent to the ICP antenna as the source of the extra heating.

We are reporting on the development of a diode-pumped chirped-pulse-amplification (CPA) laser system based on Yb:YAG thin-disk technology with a repetition rate of 100 Hz and output pulse energy in the joule range. The focus lies with the first results of the preamplifier--a regenerative amplifier (RA) and a multipass amplifier (MP). The system consists of a front end including the CPA stretcher followed by an amplifier chain based on Yb:YAG thin-disk amplifiers and the CPA compressor. It is developed in the frame of our x-ray laser (XRL) program and fulfills all requirements for pumping a plasma-based XRL in grazing incidence pumping geometry. Of course it can also be used for other interesting applications. With the RA pulse energies of more than 165 mJ can be realized. At a repetition rate of 100 Hz a stability of 0.8% (1sigma) over a period of more than 45 min has been measured. The optical-to-optical efficiency is 14%. The following MP amplifier can increase the pulse energy to more than 300 mJ. A nearly bandwidth-limited recompression to less than 2 ps could be demonstrated.

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In this work, a novel laser-produced plasma source is presented which delivers pulsed broadband soft X-radiation in the range between 100 and 1200 eV. The source was designed in view of long operating hours, high stability, and cost effectiveness. It relies on a rotating and translating metal target and achieves high stability through an on-line monitoring device using a four quadrant extreme ultraviolet diode in a pinhole camera arrangement. The source can be operated with three different laser pulse durations and various target materials and is equipped with two beamlines for simultaneous experiments. Characterization measurements are presented with special emphasis on the source position and emission stability of the source. As a first application, a near edge X-ray absorption fine structure measurement on a thin polyimide foil shows the potential of the source for soft X-ray spectroscopy.

The assumption of thermodynamic equilibrium in low-temperature plasmas can lead to errors in determination of electron energy distribution functions (EEDFs) using optical diagnostics. Significant improvements in the accuracy of EEDFs determined using optical diagnostics on argon-containing inductively coupled plasmas (ICPs) are possible by fitting an analytic representation of the EEDF with two adjustable parameters (x and T x ) to recorded optical emission spectra. This so-called x-form of the EEDF captures the well-known suppression of the high-energy portion of the EEDF (compared with the Maxwellian form) observed in ICPs. A review of electron kinetics summarizes the physical mechanisms that lead to this form, and explains the weak dependence of x on operating pressure. For the 1-25 mTorr pressure range of argon-containing mixtures in the system examined, the fixed value x = 1.2 is found to represent the EEDF very well, followed by a near linear increase in x with pressure from x = 1.2 to 1.6 in the 25-50 mTorr range. Significantly improved agreement between predictions of effective electron temperature with a global model and both probe and optical measurements when a Maxwellian EEDF is replaced by the x-form further highlights the benefit of the x-form in improved accuracy in determining the EEDF with optical diagnostics.