The plasma induced when laser interacts with matter (solid, gas, etc.) can radiate a wide range of electromagnetic waves. Its electromagnetic radiation bands range from extreme ultraviolet, ultraviolet, visible, infrared, terahertz to radio frequency microwave. Radiation in these wavelength bands has a wide range of applications, so it is of great significance to study laser plasma radiation. We studied the characteristics of nanosecond laser (1064nm, 8ns) induced plasma optical radiation. The influence of the laser parameters on the plasma radiation intensity and the time evolution of the radiation were obtained. Furthermore, we the obtained effect of the characteristics of the target on the radiation characteristics of the plasma. Finally, we calculated the electron temperature of the air plasma. The experimental results show that: the linear spectrum in the visible spectrum of laser-induced air plasma is mainly the ion spectrum of nitrogen and oxygen; as the laser energy increases the intensity of visible light radiation of air and Al plasma is gradually increasing; when the delay is 15ns, the spectral line intensity reaches the maximum; as the laser energy increases, the plasma electron temperature increases.
Fenbendazole is one kind of benzimidazole derivatives which is widely used in the treatment of parasitic infections. Because the drug action mechanism of fenbendazole is consistent with many anticancer drugs and the price is cheaper, it is considered as a potential new anticancer drug, which has caused extensive research attention. Traditional fenbendazole research methods are mostly chemical methods such as liquid chromatography. Although these methods have high precision, they have the disadvantages of cumbersome steps, high cost, and the need for specialized technicians to operate. The research method of molecular vibration information of fenbendazole has not been reported yet. In this paper, the density function theory B3LYP/6-31G* basis set and the pseudopotential basis set Lanl2dz were used to optimize and calculate the Raman activity spectrum of fenbendazole and the theoretical enhanced activity spectrum of Au as the substrate. The characteristic peaks of fenbendazole at 1093cm-1 , 1453cm-1 , 1534cm-1 , and 1633cm-1 were significantly enhanced. These characteristic peaks can be used for qualitative and quantitative analysis of fenbendazole. The causes of the difference between the theoretically calculated Raman activity spectrum and the experimental Raman spectrum are analyzed. The enhancement principle of Raman activity spectrum with Au substrate was also described. The research results will provide theoretical support for the study of the molecular properties of fenbendazole.
Radio frequency (RF) emissions in the range of 30 ~ 800 MHz from laser induced air plasma by a 532 nm nanosecond laser are investigated. The RF emissions from air plasma induced by different laser energies and laser polarization are obtained. It is noted there is no consistency of the radio frequency emission with the change of laser energy. Unlike the optical emissions from plasma, which origins from electron transition between energy levels, RF radiation generates from oscillation of electric dipoles in plasma. The space distribution of the electric dipoles in plasma is not symmetrical along the laser propagation direction. As the laser parameters change, the distribution of the electric dipoles varies, so the radio frequency emissions do not change continuous. The RF signal of air plasma is found to depend on laser polarization directions and laser energy. The amplitudes of RF emissions are observed first increase and then decrease with further increase of laser energy, which is due to higher of ionization degree and electron density at larger laser energy, thus made the RF radiation quickly decay. The dominant frequencies and amplitude of RF emissions were observed vary with the laser polarization direction, and it is found that the maximum amplitude of the output of RF emissions were detected when the polarization direction of laser beam is along the axis of the antenna and minimum when the polarization direction of the laser beam is perpendicular to the axis of the antenna. Potential physical mechanism responsible for laser parameter dependent on RF emission, rich emission lines of air plasma was discussed.
Compared with the traditional spectral analysis methods, such as inductively coupled plasma mass spectrometry method, atomic absorption spectrometry method, the analysis sensitivity, accuracy and spectral resolution of the laser induced breakdown spectroscopy technology is relatively lower. Due to the advantages o f low ablation thresholds, high-spatial resolution, minimal invasion, high-efficiency transportation of femtosecond laser, the femtosecond laser induced breakdown spectroscopy method (fs-LIBS) has become an active topic in recent years. In order to further improve the analysis performance of fs-LIBS, the spatial confinement method is proposed. In this paper, the cavity confinement enhancing effect of fs-LIBS is discussed. Based on the local thermal equilibrium condition (LTE) assumption, the plasma temperature and electron density is obtained. The results shown that the plasma emission intensity, plasma temperature and electron density are improved under the given cavity constraints. In effect, the plasma generated shock wave encounters cavity barriers during its expansion, the shock wave is reflected back to the plasma center. One hand is improved the plasma temperature and electron density, on the other hand is increased the number of particles in the upper energy level, which leads to an increase in the intensity of the plasma emission spectrum. In general, the spatial confinement method combined with the fs-LIBS showed its great potential in improving the figures-of-merit of ultrafast optical LIBS technology.
Laser induced breakdown spectroscopy (LIBS) is a promising technique, analyzing spectrum of plasma, to detect elements of solid, liquid or gaseous samples. It has many advantages, including in-situ and online detection, remote analysis, non-preparation of samples, and simultaneously multi-elements detection. Aiming at detecting detrimental elements in the polluted river and water, in this paper, collinear dual-pulse (DP) Laser-induced breakdown spectroscopy (LIBS) with liquid jet was employed to analyze emission spectrum of Cu element in the CuSO4 solution. We investigated the effect of laser pulse energies ratio and time delay between two lasers on signal intensity, which were simply given by theoretical model in laser-induced plasma for explaining various behaviors of emission spectrum. It was inferred that the maximum signal enhancement of DP-LIBS experiment was roughly 4.5 times greater than that of SP case. The limit of detection (LOD) of Cu using DP-LIBS was approximately 15 times lower than that of SP-LIBS. Results of this research indicate that collinear DP-LIBS is an effective approach to improve the plasma emission intensity and reduce the value of LOD, the application of which can be considered into the environmental problem of the water pollution.
In this paper, the laser damage thresholds of the quartz glass with/without HF acid etching are investigated induced by the wavelength of the 355nm and 1064nm respectively. Laser-induced damage threshold of the quartz glass can be improved by optimizing the HF concentration and etched time. The experimental results shown that laser induced damage thresholds of quartz glass for 355nm and 1064nm were 7.1×108 W/cm2 and 1.15×109 W/cm2 respectively, after HF acid treatment with the 10% HF concentration and etched time 15 minutes, laser induced damage thresholds of quartz glass for 355nm changed to 1.29×109 W/cm2 and improved 81.7%, while for 1064nm changed to 1.73×109 W/cm2 and improved 50.4%. The surface damage morphologies of quartz glass induced by the 355nm and 1064nm with/without HF acid etching were comparative analyzed. Finally, the laser induced damaged mechanisms of quartz glass for 355nm and 1064nm were given.
Characteristics of shock wave as well as its evolution of aluminum plasma produced by nanosecond YAG laser is investigated by time-resolved optical shadowgraph images. Experimental results show that shock wave is strongly influenced by the laser parameters and target arrangement. Shock waves from aluminum plasma and air plasma are observed simultaneously by shadowgraphs when the distance from lens to target surface (DLTS) is longer than the lens focal length, and a narrow bright “line” is observed in the region where shock waves from Al plasma and air plasma meet. The longitudinal expansion velocity of shock wave from Al plasma is largely influenced by DLTS and laser intensity as well, and it increases with laser intensity at the early stage of plasma expansion and reach to a maximum of 8.1×104 m/s.