Laser-induced breakdown spectroscopy; Femtosecond laser; Double-pulse; Enhancement mechanism;INDUCED BREAKDOWN SPECTROSCOPY; SIGNAL ENHANCEMENT; METALLIC SAMPLES; OPTICAL-EMISSION; ABLATION; NANOSECOND; SILICON; ALUMINUM; SINGLE; COPPER

A dual-wavelength femtosecond double-pulse laser is used to induce the Cu plasma spectroscopy in air. The laser wavelengths are a fundamental wavelength (800 nm) and a second harmonic wavelength (400 nm) from Ti:sapphire laser. The inter-pulse delay of double-pulse is from 300 ps to 160 ps. The observed spectral intensity is dependent on the inter-pulse delay of the dual-wavelength femtosecond double-pulse. We analyze the characteristics of the plasma temperature and the electron number density on the inter-pulse delay of double-pulse with two different wavelengths. For 800 nm + 400 nm, the spectral emission enhancement is based on more material ablation. For 400 nm + 800 nm, the enhanced mechanism is plasma reheating effect. This study will provide a better way to understand the mechanism of femtosecond double-pulse LIBS. (C) 2017 Elsevier Ltd. All rights reserved.

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; femtosecond laser; double-pulse; signal enhancement;INDUCED BREAKDOWN SPECTROSCOPY; AIR; IRRADIATION; ABLATION; DAMAGE; FILMS

In this paper, we present a study on the influence of interpulse delay in laser-induced silicon plasma with femtosecond double-pulse, and two subpulses have different laser energies. The optical emission line collected by a lens is the Si (I) at 390.55 nm. The range of double-pulse interpulse delay is from -150 ps to 150 ps. Unlike the femtosecond double pulses with two same energies, the combination of low + high energies can enhance the spectral emission intensity, while the combination of high + low energies probably reduces the spectral line intensity compared with single-pulse femtosecond laser. The results indicate that the interpulse delay is very important for laser-induced breakdown spectroscopy with femtosecond double-pulse to improve the optical emission intensity.

Q-SWITCHED NDYAG; EMISSION ENHANCEMENT; OPTICAL-EMISSION; PLASMA; SPARK

In this study, we observed the evolution of the spectral emission intensity of a glass sample with the increase of sample temperature, laser energy, and delay time in femtosecond laser-induced breakdown spectroscopy (fs-LIBS). In the experiment, the sample was uniformly heated from 22 degrees C to 200 degrees C, the laser energy was changed from 0.3 mJ to 1.8 mJ, and the delay time was adjusted from 0.6 mu s to 3.0 mu s. The results indicated that increasing the sample temperature could enhance the emission intensity and reduce the limits of detection, which is attributed to the increase in the ablated mass and the plasma temperature. And the spectral intensity increases with the increase of the laser energy and the delay time, however, the spectral line intensity no longer increases when the laser pulse energy and delay time reach a certain value. This study will lead to a further improvement in the applications of fs-LIBS. Published by AIP Publishing.