Exploration Of The Trace Detection And Preparation Of Superhydrophobic Materials By Femtosecond Laser Filaments

Femtosecond Laser-Induced Breakdown Spectroscopy?fsLIBS?is a new technology that has attracted much attention in recent years.Because of its real-time,accurate,super and super fast characteristics,it has a promising application prospect in metal smelting,soil detection,laser ablation and other applications.The fsLIBS technology presents high detection efficiency and low detection limit in the application of detection of chemical components for the advantages of little injury,can quickly get the sample detection results.It attacts much attention in recent years for the application problems of the inspection and testing in soil,metal materials,food and other fields.At the same time,compared with nanosecond laser and picosecond laser,femtosecond laser has the characteristics of super fast and strong,which can produce the smallest thermal influence and destruction.Therefore,it has widely application prospects in fine processing,laser ablation surface treatment technology and other fields.With the propagation of femtosecond laser in the air,the intensity of self focusing produced by Kerr effect becomes much higher.Eventually,it will reach the ionization threshold of molecules in air,and thus generate plasma,which has effect of defocus.When Kerr self focusing effect,diffraction and plasma defocusing effect achieve a dynamic balance,a stable plasma channel will be formed,this process is called filamentation.Since the filamentation was first observed in the experiment,its application in terahertz emission,remote sensing,air atmosphere laser generation and other fields has attract extensive attention.After the filamentation of femtosecond laser pulse in the air,the remaining plasma will emit fluorescence fingerprint after a complex conversion.Measuring spectrum along the path of propagation,we can not only extract the laser intensity of the plasma density,electron temperature and laser intensity in filamentation,but also observe the excitation and ionization processes in filamentation.In addition,because of its high sensitivity,non-contact,and real-time analysis of laser induced fluorescence,it has been widely used in remote sensing atmosphere tracking species.LIBS experiments were performed using femtosecond laser filamentation,which can measure electron temperature,plasma density,plasma spectrum and other important indicators of the sample more effectively,the development of filamentation technology provides a more stable laser source for LIBS technology,and eliminate the measurement error caused by the fluctuation of the light source or the sample surface irregular problems.First,this paper investigates the back propagation and lateral fluorescence emission in experiment during the femtosecond filamentation process in the air.Through the comparison of the circular and linear polarization of fluorescence emission,we found that for the short focal length,the direct ionization of N₂ greatly affects the behavior of fluorescence emission:in the linear polarized laser field the fluorescence from N₂⁺and N₂ are stronger,and the mechanism in fluorescence emission of nitrogen induced by femtosecond filamentation was further discussed.Secondly,we measured the spectral intensity of Cu plasma along the length direction of the filament by using the femtosecond laser induced breakdown technology,and obtained the relationship of strength distribution between different samples and distances of focusing lens.Because of the optical clamp effect,the spectrum induced by laser filamentation has relatively strong laser radiation intensity in a widely range.Meanwhile,temperature and electron density of the plasma are calculated using the Boltzmann diagram and the Stark broadening during filamentation distance reproduction,and the results is as follow:when the focus position is strong,the plasma temperature is high and the electron density is low.Conversely,when the position of self focusing is weak,the plasma temperature is low and the electron density is high.Finally,superhydrophobic surface of Aluminum Alloy material is prepared using the properties of femtosecond laser filamentation.Furthermore,the relationship between contact angle elements?groove width,laser intensity,laser polarization direction and scanning speed?and superhydrophobic structure are also discussed.