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; DOUBLE-PULSE; OPTICAL-EMISSION; CAVITY CONFINEMENT; TEMPERATURE; IMPROVEMENT; SILICON

The effect of spatial confinement on femtosecond laser-induced Cu plasmas was investigated by time-resolved spectroscopy. The cylindrical cavities with various diameters (2 and 3 mm) and various heights (2, 3, and 4 mm) were placed on the sample surface. An obvious enhancement in the emission intensity of Cu atomic lines was observed when a cylindrical cavity was used to confine the femtosecond laser-induced Cu plasmas. The results showed that enhancement ratios in femtosecond laser-induced breakdown spectroscopy with spatial confinement varied with cavity diameters and atomic emission lines selected. The spatial confinement effect was not significantly influenced by the cavity height because the height of plasma plume is lower than the cavity height. The maximum enhancement ratio for the emission intensities of the Cu atomic lines was measured to be around 3 at a time delay of 3.5 mu s when the cavity diameter is 2 mm. The spectral enhancement is attributed to the compression of the plasma by the reflected shock wave. Published by AIP Publishing.

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.