Study On Energy Gap In Some Superconducting Materials By Point Contact Spectroscop

High harmonic spectroscopy brings people’s cognition of the microscopic world to the attosecond time scale of electronic motion.People have developed a series of methods to extract the structure and dynamics information of the system from the harmonic radiation spectrum based on the characteristics of atoms and symmetric molecules that only generate odd harmonics in a monochromatic field due to the definite parity of the wave function.However,these methods cannot be directly applied to asymmetric molecules that can produce both odd and even harmonics due to symmetry breaking.Therefore,the ultrafast detection of asymmetric molecules has become a hot issue in the study of higher harmonic spectroscopy.In this paper,we explore how to use harmonics to probe the structure of asymmetric molecules with complex symmetries by in-depth analysis of the influence of asymmetric molecular tractory on harmonic emission.In addition,the Coulomb effect also has important effects on harmonic emission,and these effects need to be fully analyzed in the scheme of using harmonic emission to probe the ultrafast dynamics of electrons.In this article,we discuss the related effects in depth by developing a theoretical model of harmonic emission that includes the Coulomb effect.Firstly,we study odd-even high-harmonic generation(HHG)of orientation asymmetric molecules with different symmetries in strong laser fields.Based on the strong-field approximation model,we give the different ionization-recombination HHG route expressions that contribute to the odd-even harmonic.And conclude that each harmonic has two generating channels.The comparison of the HHG yields of full routes with one specific route demonstrates that the routes where the electron ionizes from the gerade component of the asymmetric orbital mainly contributes to odd-even HHG,while the routes of ionization from the ungerade component of the asymmetric orbital contributes less to the generation of the odd and even harmonics.So we define these two channels as main and minor routes.Our results show that this is determined by the nature of the tunneling ionization of asymmetric molecules in strong laser fields.During the tunneling process,when bound electrons pass through the potential barrier formed by the combined action of the laser field and the asymmetric Coulomb potential,they will Influenced by the interference of different channels in tunnel ionization.the important influence of molecular structure on odd and even harmonic yields is indirectly illustrated.In this paper,we also discussed the influence of different emission routes on the odd-even harmonic asymmetric orbit imaging,which provides help for the application of odd and even harmonic radiation in higher harmonic spectroscopy.Then,we study parallel and perpendicular odd-even high-harmonic generation for oriented asymmetric molecules with complex symmetries in one-color laser field.By solving the Schr?dinger equation(TDSE)that is consolidated from oriented asymmetric molecules,we calculated the yields of parallel and perpendicular odd-even harmonics at different angles.Our simulations show that HHG of asymmetric molecules is sensitive to molecular structure.At the same time,on this basis,we use the molecular structure to consider the symmetry of the wave function in the plane wave approximation,and propose a concise and effective model to predict the production of parallel and vertical odd-even HHG.This model can also be applied to different molecular orientations and various laser intensities and other asymmetry molecules that do not have node planes,opening up possibilities for a wide range of applications and providing a reference for experiments involving harmonic yields of asymmetric systems.At the same time,we also study the impact of the strong field ionization time delay(response time)caused by the Coulomb effect on the subsequent ultrafast dynamics of electrons。After tunneling out of the laser-Coulomb barrier,the movement of tunneling electrons will still be affected by the Coulomb potential.Our research has shown that this Coulomb effect causes a large time difference(greater than 100attoseconds)between the time for electrons to tunnel out of the barrier and the ionization time when electrons are free.This large time difference has an important impact on strong field processes such as above-threshold ionization and high-order harmonic generation,significantly changing the time-frequency characteristics of electron orbitals.We subsequently performed semi-quantitative analysis of these effects,providing new insights into the study of strong-field physics and attosecond measurements.Finally,we numerically and analytically study the influence of Coulomb potential on high-order harmonic generation.We are concerned about the effect of the Coulomb potential on the emission time of HHG associated with a specific electron orbit.By using a numerical program based on the numerical solution of the three-dimensional time-varying Schr?dinger equation,we extracted the HHG emission time of the long electron trajectory and the short electron trajectory.We compare the predictions of the strong-field approximation(SFA)with the developed Coulomb-modified strong-field approximation model(MSFA)using the TDSE predictions as a reference.The results show that compared to the previous SFA model,the revised model predicts earlier harmonic emission times due to the inclusion of the Coulomb effect.This effect has different effects on the emission time of long and short electron trajectories,and also has a more significant impact on low-energy harmonics than high-energy harmonics.In addition,it changes the HHG amplitudes of the long and short electron trajectories.We also use different laser parameters and Coulomb potential forms to verify our discussion.The results provide strong support for our proposed HHG model including the Coulomb effect.