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Register a new userEffect of laser intensity and dynamics of plasma on laser induced breakdown spectroscopy
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Laser-induced breakdown spectroscopy (LIBS) show enhancement in its signal, when the laser-induced plasma is confined/decelerated under the effect of an external steady magnetic field or in a small cavity. An enhancement in LIBS signal has been observed ~2 times in the case of magnetic confinement. Combination of magnetic and spatial confinement provide enhancement by an order of magnitude. Theoretical analysis of the decelerated plasma has been found in agreement with the experimental observations. The enhancement in LIBS signal is found dependent on the efficiency of plasma confinement as well as on the time duration of laser. The saturation in LIBS signal at higher laser intensity is found correlated with electron-ion collision frequency as well as on the dynamics and instability of plasma plume. Possibility of further enhancement in emission has also been discussed.
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This paper presents the process of plasma formation during laser induced breakdown spectroscopy (LIBS) along with analysis of emission from double pulse LIBS to better understand the processes and the factors involved in enhancement of plasma emission. In this analysis plasma emission has been considered directly proportional to the square of plasma density, its volume, and the fraction of absorption of second laser pulse in the plasma plume produced by the first laser through inverse Bremsstrahlung absorption process. The electron ion collision frequency, which is dependent on the density and temperature of the plasma, has been found playing important role in the enhancement of emission as well as in the saturation of emission during LIBS. The effect of material ablation, delay between lasers, plasma confinement and shielding effect has also been discussed.
The influence of ns-laser wavelength to discriminate ancient painting techniques such as are fresco, casein, animal glue, egg yolk and oil was investigated in this work. This study was carried out with a single shot laser on samples covered by a layer made of a mixture of the cinnabar pigment and different binders. Three wavelengths based on Nd: YAG laser were investigated (1064, 532 and 266 nm). The plasma is controlled at the same electron temperature after an adjustment of pulse energy for these three wavelengths on a fresco sample without organic binder. This approach allows to eliminate the effects of laser pulse energy and the material laser absorption. Afterwards, the emission spectra were compared to separate different techniques. The organic binding media has been separated based on the relative emission intensity of the present CN or C 2 rovibrational emissions. In order to test the capability of separating or identifying, the chemometric approach (PCA) was applied to the different matrix. The different solutions in term of wavelength range to optimise the identification was investigated. We focused on the evaluation for the laser wavelength to insure a better separation. The different capacity was interpreted by differentiating 1 Corresponding author. E-mail address: [email protected] 2 the binders by the altered interaction mechanisms between the laser photon and the binders. Also, the electron temperature in the plasma was estimated, which provided the evidences to our findings.
An ultrarelativistic electron beam passing through an intense laser pulse emits radiation around its direction of propagation into a characteristic angular profile. Here we show that measurement of the variances of this profile in the planes parallel and perpendicular to the laser polarization, and the mean initial and final energies of the electron beam, allows the intensity of the laser pulse to be inferred in way that is independent of the model of the electron dynamics. The method presented applies whether radiation reaction is important or not, and whether it is classical or quantum in nature, with accuracy of a few per cent across three orders of magnitude in intensity. It is tolerant of electron beams with broad energy spread and finite divergence. In laser-electron beam collision experiments, where spatiotemporal fluctuations cause alignment of the beams to vary from shot to shot, this permits inference of the laser intensity at the collision point, thereby facilitating comparisons between theoretical calculations and experimental data.
Quantitative evaluation of tunable diode laser induced fluorescence (TDLIF) measurements in magnetized plasma take into account Zeeman splitting of energetic levels and intra-multiplet mixing defining the density distribution (alignment) of excited $mathrm{2p_8}$ multiplet is discussed in this paper. TDLIF measurements were used to evaluate light-transport properties in a strongly magnetized optically thick argon plasma under different pressure conditions. Therefore, a coupled system of rate balance equations were constructed to describe laser pumping of individual magnetic sub-levels of $mathrm{2p_8}$ state through frequency separated sub-transitions originating from $mathrm{1s_4}$ magnetic sub-levels. The density distribution of $mathrm{2p_8}$ multiplet was described by balancing laser pumping with losses including radiative decay, transfer of excitation between the neighboring multiplets driven by neutral collisions and quenching due to electron and neutral collisions. Resulting $mathrm{2p_8}$ magnetic sub-level densities were then used to model polarization dependent fluorescence, consider self-absorption, which could be directly compared with measured polarization resolved TDLIF measurements. This enables to obtain unique solutions for the $mathrm{1s_4}$ and $mathrm{1s_5}$ magnetic sub-level densities which were in good agreement with the densities obtained by laser absorption measurements. It is shown that LIF measurements in magnetized plasma conditions have strong pressure dependence that should be corrected consider effective disalignment rate. The presented measurement method and model can help further understanding and improve description of optical emission of argon in magnetized conditions.
An overview from the past and an outlook for the future of fundamental laser-plasma interactions research enabled by emerging laser systems.
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