Spatial-time behavior of transversally excited pulsed volume discharge in argon is investigated by spontaneous emission
spectroscopy and different imaging techniques. VUV Ar<sub>2</sub>* emission, UV-VIS continuum and Ar* red lines are used for
direct monitoring of discharge homogeneity in the breakdown and recombination stages. Experimental data indicate that
Ar* atoms and Ar<sub>2</sub>* excimers are created exclusively in the positive column of the discharge, not in near-cathode zones.
These zones (cathode sheath and negative glow), however, are the main sources of UV-VIS continuum. The discharge is
homogeneous during the first powerful breakdown pulse and fills the whole space between electrodes. Secondary
excitation pulses initiate oscillations of plasma emission and longitudinal fragmentation of the discharge into separate
zones. Fragmentation is connected with dynamical change of the electron emittance of heated and cold electrodes.
Additional electrons, produced during secondary excitation pulses, convert effectively the reservoir of long-lived triplet
Ar<sub>2</sub>* molecules to fast-emitted singlet Ar<sub>2</sub>* excimers - sharp spikes of VUV (126 nm) emission are observed. Double-pulse
discharge pumping regime is suggested for easier achievement of the lasing threshold for rare gas excimer lasers.
Theoretical and experimental studies of low temperature plasmas of inert gas mixtures show a very high efficiency for energy transfer from broad vacuum ultravio let (VUV) continua to narrow spectra. The process of energy transfer can not be explained as an ordinary particle collision mechanism. Narrow band light amplification in plasmas of inert gas mixtures is discussed as a possible process of energy transfer.
Spatial-time behavior of the main excited atomic and molecular excimer species were monitored with ns-gated ICCD camera (200-850 nm) and solar-blind PMT (115-300 nm) from spontaneous emission spectra of homogeneous volume discharge in high-pressure (up to 10 bar) argon. It is revealed, that broad (200-700 nm) UV-VIS continuum is caused
mainly by radiative recombination of free plasma electrons with Ar<sub>2</sub><sup>+</sup> ions. Emission intensities from this continuum and red Ar<sup>*</sup> lines have a typical recombination behavior in the afterglow stage of the discharge (square root of its intensity is proportional to the electron density). Observed UV-VIS continuum spectrum is modeling by free-bound photorecombination transitions to manifold of 4s, 4s, 4p, 4p, 3d, 3d Ar<sup>*</sup> levels. Peak intensity of the second continuum VUV emission from Ar<sub>2</sub><sup>*</sup> excimers (126 nm) increases approximately quadratically with the gas pressure. This behavior is observed at pressure range of 1-2 bar, however at higher pressures the peak intensity has a tendency to the saturation. VUV emission from Ar<sub>2</sub><sup>*</sup> <sup>1</sup>Σ<sub>u</sub><sup>+</sup> (0) molecules increases during small-power secondary pumping pulses due to better mixing of singlet <sup>1</sup>Σ<sub>u</sub><sup>+</sup> and triplet <sup>3</sup>Σ<sub>u</sub><sup>+</sup> Ar<sub>2</sub><sup>*</sup> states by additional electrons.
Homogeneous volume discharge in high-pressure (up to 10 bar) argon is studied as a possible active medium for Ar<sub>2</sub> VUV (126 nm) laser. Time dependences of the densities of Ar<sup>*</sup> (4s, 4p), Ar<sub>2</sub><sup>*</sup> 4sσ a<sup>3</sup>Σ<sub>u</sub><sup>+</sup> (v=0) were measured by the pulse dye laser absorption probing of the discharge plasma. Experimentally obtained temporal dependencies of several excited species are compared with calculated ones. Strong optical dynamic aberrations in the discharge plasma are observed for the probing laser beam. Nonuniform distribution of the pumping power density in the transverse cross section of the discharge is the reason of free electrons gradient. These phase aberrations are caused by negative contribution of free electrons to the refraction index.
The aim of this work is spectroscopic diagnostics of a discharge in a new compact 'sealed-off' excimer laser. Spatial-time behaviors of the main excited atomic and ionic species, gas temperature and electron density were monitored with ns-gated ICCD camera from spontaneous emission spectra of the discharge. Ignition of cathode hot spots is detected from atomic emission lines of a cathode material. At increased current density cathode hot spots appear after the end of the pumping pulse because of delayed explosion of overheated emission centers on the cathode surface. No constrictions have been developed in the discharge from these spots because the pumping is very short. At highest pulse repetition rate discharge constriction is initiated from accumulated overheating of the boundary gas layer near the cathode surface.
The spectral, temporal, and spatial influence of a dye-laser-induced preionization for XeCl discharge-pumped lasers has been measured. Positive or negative response of amplified spontaneous emission (ASE) in the laser active medium on an additional preionization is dependent on the pumping power density and HCl concentration. Mechanisms of additional free electrons creation and decay have been discussed for VIS and UV pulsed preionization.
The results of comprehensive investigations of a compact UV-preionized XeCl laser are presented. It has been shown that the gas lifetime increased to more than three times if BCl<sub>3</sub> was used as a halogen donor instead of HCl. The analysis of chemical degradation products suggests the possibility of a 'self-regeneration' of BCl<sub>3</sub>-containing gas mixtures, where volatile contaminants can be converted into solid products. The temporal and spatial dependences of the densities for several plasma components: Ne<sup>*</sup>, Xe<sup>*</sup>, Xe<sup>+*</sup>, Cl<sup>-</sup>, XeCl<sup>*</sup> and boron atoms were measured by the dye laser absorption (gain) probing. The halogen donor depletion in volume and constricted phases of the discharge was traced by the temporal dependence of the ground-state boron atoms density. The evolution of filamentary instabilities in the discharge was monitored from the Stark broadening of Xe<sup>*</sup> absorption lines.