Electron Density In Laser-induced Plasma Research Articles

Influence of target temperature on H alpha line of laser-induced silicon plasma in air

This study mainly discusses the effect of target temperature on the emission intensity of the H alpha line in laser-induced silicon plasma in an atmospheric environment. The sample was uniformly heated to temperatures ranging from room temperature (22 °C) to a high temperature (300 °C) with laser energy ranging from 5.5 mJ to 11.5 mJ. Emission lines of Si (I), Si (II), and H (I) were observed. The H alpha line was attributable to a small amount of water vapor derived from natural humidity in the surrounding air. The H alpha line was widely used to measure electron density in laser-induced plasma. The results show that an increase in the sample temperature improved the spectral intensity of the Si line, whereas the emission intensity of the H alpha line declined. The reduction in the H alpha line was due to lower air density near the heated target surface. This investigation enhances the understanding of laser-induced breakdown spectroscopy applications at higher sample temperatures.

Laser plasma diagnostics and self-absorption measurements of the Hβ Balmer series line

In this work, the peak-separation of the Balmer series hydrogen beta line was measured to determine the electron density of laser-induced plasma from spatially and temporally resolved spectra collected in laboratory air at standard ambient temperature and pressure. The self-absorption phenomenon is investigated by using a mirror that retro-reflects the emitted radiation through the plasma. The experimental data with and without the mirror were analyzed with available hydrogen beta computer simulations. Hardly any self-absorption was found as indicated by the correction factors that only marginally differ from unity. The obtained electron density values are also compared with the electron densities from nearby nitrogen lines. The hydrogen beta Hβ peak-separation method yields reliable results for an electron density of the order of 1×1017cm−3 for time delays of 5μs from plasma generation, which confirms that self-absorption is insignificant for such electron densities.

Interferometric System for the Visualization of High-Speed Processes in Laser Plasma

A fundamental to understanding physical processes in laser plasma is to study plasma density profile. We applied an optical interferometer of Mach-Zehnder and UV nitrogen laser that was used as a source of probe light (wavelength 337 nm, energy of ∼ 150 μJ, pulse duration ∼ 5 ns). Digital camera frame grabber captures individual interferometric pictures, so phase shift of fringes is easy photographed and analyzed in terms of plasma density. Powerful Nd-laser (wavelength 1.054 μm, pulse energy up to 20 J, pulse duration ≈15 ns) was used to generate laser plasma. The pulse of probing laser passed through the laser-induced plasma with delay td ≈5÷50 ns. The results of interferometric measurements of electron density in laser-induced plasma from copper target are presented.

Determination of the local electron number density in laser-induced plasmas by Stark-broadened profiles of spectral lines: Comparative results from H α, Fe I and Si II lines

Measurements of the local electron density in laser-induced plasma have been carried out from the Stark-broadened profiles of three reference lines (H α, Fe I and Si II). The plasma has been generated from a Fe–Si sample in air using a Nd:YAG laser. Compatible values of the local electron density have been obtained from the three lines. The experiment is based on the use of an imaging spectrometer, the capability for spatial resolution of a charge-coupled device and the application of a spatial deconvolution procedure to the spectra. Distributions of the emission coefficient have been obtained, showing that the three lines are emitted from different regions of the plasma. The implications in the apparent electron density values obtained in spatially-integrated measurements are discussed: similar values are obtained for the H α and Si II lines, while the Fe I line leads to a 25% lower value.

Spatio-temporal dynamics of electron density in femtosecond laser microplasma of gases

The formation and evolution of femtosecond laser plasma produced in microvolumes of gases at different pressures upon their multiply ionization by high intensity pulses of fundamental and second harmonics of a Ti:sapphire laser is studied. The interferometric technique for precise ultrafast optical diagnostics of such plasma was applied. The numerical technique of interferogram processing and reconstruction of instant spatial distribution of refractive index and free electron density in laser-induced plasma applied for this proposes is described. The spatiotemporal distribution of the refractive index and free electron density were studied with a spatial resolution of ∼1 μ m and a temporal resolution of ∼70 fs.

Laser-induced breakdown spectroscopy: flat surface vs. cavity structures

Cavity formation is a common phenomenon involved in solid-state analysis when repetitive laser pulses are applied to induce breakdown spectra. While previous LIBS investigations have been mostly focused on laser ablation on flat surfaces, the development of a laser-induced plasma inside cavity structures is of both fundamental and practical significance for quantitative chemical analysis using LIBS. In this paper, we attempt to answer the question, to what extent cavity formation would influence the temperature and electron density of laser-induced plasma. We found a significant effect of cavity aspect ratio on plasma characteristics, in particular, the measured high temperature and electron density of laser-induced plasma inside cavity structures.