Absorption and emission spectra of the YBCO laser plume

Abstract

The plasma produced during laser ablation deposition of thin film YBCO has been studied by optical emission spectroscopy. There is evidence of increased YO band emission in the range 590-625 nm as the ambient oxygen gas pressure confining the plume is increased in the range 30-200 m Torr. Temporal profiles show that close to the target the plume is insensitive to ambient oxygen pressure. It is deduced that the optical emission here is excited by electron impact excitation. Further away from the target there is evidence that two distinct processes are at work. One is again electron excitation; the emission from this process decreases with distance because the expanding plmne cools and collisions become less frequent in the expanding gas. The second is driven by oxidation of atomic species expelled at high speeds from the target. The main region of this activity is in the plume sheath where a shock front ensures heating of ambient O2 and reaction of monatomic plasma species to form oxide in an exotherrnic reaction. Spatial mapping of the emission demonstrates clearly how increasing oxygen gas pressure confines the plasma and enhances the emission intensity from the molecular YO species ejected from the target in a smaller region close to the target. Ba + is observed as a dominant species only very close to (within 1 mm of) the target. Absorption spectra have been taken in an attempt to examine ground state and cool species in the plume. They reveal the quite surprising result that YO persists in the chamber for periods up to 1 msec. This suggests an explanation for the recent report of off-axis laser deposition in terms of simple condensation. Previously, quasi-ballistic transfer of material from target to substrate has been considered the only significant process.

Investigations of laser-produced plasmas from boron nitride targets

“…The fundamental processes occurring in the formation and evolution of these laser-produced plasma plumes are still not completely understood and are the focus of intense research. Many different diagnostic techniques, such as optical spectroscopy [6,7], laser-induced fluorescence [8,9], mass spectroscopy [10] and Langmuir probes [11,12], have been used in attempts to characterize the plasma as it expands either in a vacuum or in an ambient atmosphere.…”

A study of molecule formation during laser ablation of graphite in low-pressure ammonia

“…Furthermore, there is a real difficulty in obtaining nitride films without O contamination [16], and NH 3 can be used to reduce oxygen contamination during the growth of thin ‡ E-mail address: jorg.hermann@univ-orleans.fr nitride films. Among various techniques for studying laserinduced plasmas, including optical emission [15,[17][18][19], absorption [20,21], laser-induced fluorescence [22,23] and mass spectroscopy [24][25][26], optical emission spectroscopy was chosen to follow the time and space evolution of the excited state plasma species. Various transient chemical species produced during the process, such as excited atoms, ions, molecules and radicals, have been observed.…”

Temporal and spatial evolution of C2 in laser induced plasma from graphite target

“…In order to understand the processes leading to cluster formation, which may directly influence laser deposition, the mechanism of plasma plume generation from the target material under laser irradiation and the interaction of the resulting plume with the ambient atmosphere in the plasma chamber should be studied in detail. There are several techniques for characterizing laser induced plasma and these include optical emission spectroscopy, [25][26][27] optical absorption spectroscopy, 28,29 laser induced fluorescence, 30,31 time resolved spectroscopy, 32 mass spectroscopy 3 etc. Among these, time resolved spectroscopy is the most suitable method to study the dynamics of laser produced plasma.…”