Radiation Source Generated By The Interaction Of Intense Femtosecond Laser With Slab And Wire Target

Ultrashort intense laser pulse technology has been developed rapidly in recent years.The peak power of laser has reached tens of petawatts,and the peak light intensity has exceeded 1 × 1022 W/cm2.Many nonlinear physical processes occur in the interaction of ultrashort intense laser pulse with matters.They can generate electromagnetic radiation sources ranging from terahertz to gamma-ray wavelengths and particle sources.The peak brightness of these strong radiation sources can approach or exceed that of the traditional accelerator,synchrotron radiation,and free electron laser.The pulse width can be as short as picosecond,femtosecond,or even attosecond time scales.It has excellent potential for miniaturization of intense radiation source devices and is receiving increasing attention in fundamental science research,industrlications,medical and defense fields.This thesis is concerned with electron source,terahertz radiation,and gamma-ray generated by the interaction of intense femtosecond laser pulse with slab plasma and metal wire target.The correlation between terahertz wave generation and laser absorption mechanisms is investigated.We have investigated the effect of preplasma on the gamma radiation generated by an ultrarelativistic laser pulse.The double-ended emission of a wire-guided electron beam has been shown experimentally.To solve the problem of too large divergence angle of terahertz wave in conventional scheme,we have proposed and experimentally demonstrated a new method for collimated,doubleended emission of terahertz wave generated by metal wire waveguides.The main research results are:The physical processes and their correlations among fast electron emission,terahertz radiation,and high-order harmonics generation(HHG),produced by subrelativistic laser and solid targets,are investigated using the PIC simulation program.It is found that the emitted electrons and terahertz radiation first increase and then decrease,and the HHG keeps weakening.By analyzing the electron emission,terahertz radiation,HHG spectrum,and laser absorption rate,we have clarified that fast electrons generate terahertz wave through the coherent transition radiation process.Meanwhile,we have revealed that this changing pattern is caused by the transition from vacuum heating to stochastic heating of the laser energy absorption mechanism.The role of the preplasma in the interaction between an ultra-intense laser and solid target to generate gamma-ray radiation is investigated using a PIC program with a QED module.Analyzing the physical characteristics such as the energy and angular distribution of electrons,the spatial and angular distribution of gamma photons in characteristic times,we find that more radiation mechanisms carry out a joint role as the scale length becomes longer.At the optimal density scale length of the preplasma,the piled plasma mirror creates a balance between electron acceleration and laser reflection to produce the highest radiation conversion efficiency.Wire-guided to double ends electrons generated by laser has been detected simultaneously in experiments for the first time,which is expected to improve ultrafast electron diffraction technique.We have built an experimental system with multiple incidence angles and conducted an experimental study on the generation of wire-guided electron emission from the interaction of laser with metal wire.For the first time,it is found that the electron beam is guided and collimated along the wire at both ends.The wire-guided electrons are distributed in a circular pattern with high energy in the inner circle and low energy in the outer circle.When the laser is not incident vertically,the collimation of the wire-guided electrons in the direction of laser reflection deteriorates,and shadows and scattered spots appear simultaneously.Finally,with the help of PIC and numerical calculation,we have found that the wire-guided electrons of doubleended emission are generated by the transient electromagnetic field confinement on the surface of the metal wire.We have proposed and experimentally demonstrated for the first time a new method to generate double-ended terahertz radiation based on a wire waveguide.The mechanism of terahertz wave generation has been clarified,which is expected to significantly contribute to the convenient application of laser-driven strong terahertz source.It has been found that an ultrashort laser pulse irradiated wire waveguide can generate symmetrical,double-ended terahertz waves,whose symmetry does not vary with the laser incidence angle.The central frequency of the terahertz wave is about 0.2 THz and does not depend on the diameter of metal wire.The possibility of terahertz wave generation from the wire-guided electrons has been ruled out by the variation pattern of the double-ended wire-guided electrons and terahertz wave at different laser incidence angles and the intentional destruction of the guide electrons.By considering the suppression of diffraction effect about target size,which occurs in the process of terahertz generation through transition radiation mechanism,the possibility of transition radiation is also excluded.Finally,it is revealed that the terahertz radiation is generated by the interaction between the moving Coulomb field of the electron bunches and the metal wire.This process can be seen as the coherent diffraction radiation,where the wire acts as an excellent waveguide to propagate the terahertz surface wave to both ends.