INDUCED BREAKDOWN SPECTROSCOPY; ABLATION; EMISSION; SPARK

The influence of distance between sample surface and focal point on optical emission spectroscopy of laser-induced silicon plasma by a nanosecond Nd:YAG laser operating at the wavelength of 1064 nm was investigated in air. Our results show that the emission intensity of Si (I) 390.6 nm line and N (II) 399.5 nm line depends strongly on the distance between sample surface and focal point. When the surface of ablated sample is away from the focal point of focusing lens, the neutral atomic line (Si(I) signal to be measured) is much higher than the ionic line (interference signal N (II)). Therefore, we can improve the intensity of Si (I) signal to be measured, and reduce the intensity of interference signal N (II). The presented result is mainly based on the reduction of interaction between the plasma plume and the ambient air, leading to much weaker collisions. (C) 2017 Author(s).

Laser-induced breakdown spectroscopy; LIBS; lens-to-sample distance; sample positioning; repeatability;

A simple device based on two commercial laser pointers is described to assist in the analysis of samples that present uneven surfaces and/or irregular shapes using laser-induced breakdown spectroscopy (LIBS). The device allows for easy positioning of the sample surface at a reproducible distance from the focusing lens that conveys the laser pulse to generate the micro-plasma in a LIBS system, with reproducibility better than +/- 0.2 mm. In this way, fluctuations in the fluence (J cm(-2)) are minimized and the LIBS analytical signals can be obtained with a better precision even when samples with irregular surfaces are probed.

LIBS; spatial confinement; cavity height; signal enhancement;INDUCED ALUMINUM PLASMA; TIME-RESOLVED EMISSION; OPTICAL-EMISSION; MAGNETIC-FIELD; PULSE; ENHANCEMENT; ABLATION; SILICON; LIBS; OPTIMIZATION

In this paper, we present a study on the spatial confinement effect of laser-induced plasma with a cylindrical cavity in laser-induced breakdown spectroscopy(LIBS). The emission intensity with the spatial confinement is dependent on the height of the confinement cavity. It is found that, by selecting the appropriate height of cylindrical cavity, the signal enhancement can be significantly increased. At the cylindrical cavity (diameter = 2mm) with a height of 6 mm, the enhancement ratio has the maximum value (approximately 8.3), and the value of the relative standard deviation (RSD) (7.6%) is at a minimum, the repeatability of LIBS signal is best. The results indicate that the height of confinement cavity is very important for LIBS technique to reduce the limit of detection and improve the precision.

FEMTOSECOND DOUBLE-PULSE; OPTICAL-EMISSION; PLASMA; ENHANCEMENT; SILICON

The spatial confinement effect in laser-induced plasma with different distances between the target surface and focal point is investigated by optical emission spectroscopy. A Nd: YAG laser is used to produce plasma from a silicon sample in air atmosphere. When the appropriate distance is selected, the duration of spectral emission enhancement is much longer, and the enhancement effect is much stronger. The phenomenon is attributed to the aspect ratio of the lateral to axial direction of the plasma plume. The plasma plume of a large aspect ratio will interact with the reflected shockwave in a long range of delay time, leading to high particle density. This provided a better understanding about the effect of the distance between the target surface and focal point, leading to better conditions for spatially confined laser-induced breakdown spectroscopy.