Effect Of Sample Temperature And Spatial Confinement On Femtosecond Laser-induced Plasma Spectroscopy

Laser-induced breakdown spectroscopy(LIBS)is an analytical technique that utilizes a high-power pulsed laser to ablate a sample,generate a plasma on the surface and obtain the laser induced plasma emission spectrum.LIBS is widely applied due to its simplicity and convenience in elemental detection;since the whole detecting process can be completed in a short time,the sample hardly needs to be pretreated,and remote and in situ detection can be achieved with optical fibers.In spite of several advantages,its relatively poor sensitivity in comparison with other established techniques like inductively coupled plasma mass spectrometry often limits the analytical performance of LIBS.With the wide application of LIBS,studies of improving LIBS sensitivity and efficiency are of growing interest.With the rapid development of laser technique,it is easier to get ultra-short laser pulse in the femtosecond(fs)range.Compared with ns laser,the use of fs laser offers many significant advantages for LIBS,such as lower ablation threshold fluence,less fractionation vaporization,higher spatial resolution,small ablated mass and reduced sample damage.Because of the reduced sample damage and a lower ablation threshold fluence,the reproducibility of fs LIBS is improved significantly.Until now rather few works focused on studying LIBS using femtosecond laser pulses,so we use femtosecond laser in our study.This article is consists of five chapters.The first chapter introduces the principle,advantages,disadvantages,application of LIBS technology,the development status at home and abroad,and the enhancement method for spectroscopy.The second chapter introduces the theoretical background of LIBS.The third chapter investigates the femtosecond laser-induced breakdown spectroscopy of Ge with different initial temperatures.The experimental results show that the spectral intensity decreases with increasing temperature.It is found that the change in the transient reflectivity of Ge at higher temperature is less than that at lower temperature,which may be the main reason for the decrease of spectral emission intensity.The fourth chapter investigates the effect of spatial confinement on femtosecond laser-induced Cu plasma.An obvious enhancement in the emission intensity of Cu atomic lines was observed when a cylindrical cavity was placed to confine the laser-induced Cu plasma.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 ?s when the cavity diameter is 2 mm.The spectral enhancement is attributed to compression of the shock wave to the plasma.In the fifth chapter,the paper summarizes the results of this article and put forward the future prospect.