Studies On Double-exponential Decay Of Ionization For H₂⁺ Exposed To Intense Lasers

As a fundamentally important research field, atomic, molecular and optical physics (AMO) has witnessed a long history. The maturity of ultrashort and ultra-intense pulsed lasers in 1980's have, due mainly to their compatible electric field strengths with those seen by electrons in atoms and molecules, triggered another research surge in so far as interaction of intense light with atoms or molecules is concerned. Theoretically, the research endeavors have manifested themselves by revealing bunch of novel physical processes and novel concepts through investigation on ionization and dissociation. More importantly, studies in this direction have found potential values of practice in: CFI, VUV radiation, THz wave, attosecond light pulse generation, controlled chemical reactions. Numerical simulation, besides other methods, has always been a key means in investigating interactions of light with atoms and molecules.To that end, the presented dissertation focuses on the so-called charge resonance enhanced ionization (CREI) effect, by performing ample computer simulations on a real 3D H2+ system. Our research work and the obtained results are outlined:(1) Based upon the model suggested initially by Bandrauk, we adopted and implemented algorithms of expanding wavefunctions as Bessel-Fourier series and then temporally propagating them by dividing the real 3D single electron wavefunction into radial and axial components, thereby eliminating the singularities in the Coulomb potential. The initial wavefunction ansatz is exact. In our simulation, the Bessel-basis-vector number has been increased from 16 to 32,henceforth confirming the computation accuracy.(2) We simulated photoionization process of H2+ under irradiation of pulses with varying light intensity and internuclear separation at wavelengths of 800nm, 1550nm and 1064nm. Three different methods, namely the non-ionization probability, exponential fitting and double-exponential fitting, were used for getting variations of photoionization rates versus internuclear separation. What can be inferred from the studies was: H2+ system has different ionization behaviors: ionization saturation, enhanced ionization and doubly-exponentially decayed ionization.(3) Experiment design: We designed a prelimary setup of Time-of-Flight spectrometer and Imaging spectrometer, aimed for measuring ionization and dissociation fragmentation. This virtual experiment can serve for future image correlation and image labeling techniques in strong field processes in atoms and molecules. The thesis also described some practical participation in building a flash-lamp-pumped Nd:YAG laser which is supposed to provide two perspective excitation wavelengths at 1319nm and 660nm.