| As a result of the rapid development of ultra-short andultra-intense laser technology, the peak electric field strengthof lasers has reached or exceeded the coulomb field strengthseen by the electron in the ground state of atomic hydrogen.The application of such intense laser fields to the atoms leadedto the discovery of a number of novel strong-field phenomenathat can't be explained by traditional perturbation theories.The high-order harmonic generation (HHG) is one of them.The high-order harmonic generation is one of the most promisingscheme by which the possible sources of radiation in x-ray andXUV regions can be obtained. People's basis pursuit in HHG is tosimultaneously increase conversion efficiencies and reachshorter wavelengths. From the cutoff law for the HHG of asingle atom ωcutoff = Ip + 3.2Up ( Here Ip is the ionizationpotential and Up is the ponderomotiveenergy, Up = e2E02 /(4mω2) , E0 ωis the amplification of theincident laser field, ωis the angular frequency of the incidentlaser field), we notice that one of the most direct ways inextending the harmonic plateau for the single atom is toheighten the ionization potential. In order to achieve this point,we can choose highly charged ions as the target. But it isdifficult to obtain a great deal of highly charged ions inexperiment. Another direct way is to increase ponderomotiveenergy. To realize the aim, it is necessary to raise the intensityof the laser pulse when laser wavelength keeps constant.However, it is limited for an atom to be able to endure the highintensity of the laser pulse. An atom will be depletedcompletely when the laser intensity rises up to a certainthreshold amount, so that corresponding harmonic emissionprocess also terminates. To overcome this difficulty, one turnsto short pulse lasers, which provides the advantage that thedepletion of atom is avoided when relatively stronger lasersare employed. Experimentally, the energetic photons of 500evcan be generated by using the laser pulses with duration of5-7fs, which is close to one optical cycle. Therefore, the HHGplateau can no longer be extended through the furthershortening the pulse duration.In this thesis, we propose a scheme by which the radiationis extended from XUV region to γ-ray. (what scheme?) Thisscheme has two advantages. One is that the muonic atom hashigh ionization potential, about 200 times of hydrogen atomicionization potential, and this is a neutral system. Another isthat we may make muonic atom ion through enhancing thepeak amplitude of laser field and the correspondingponderomotive energy has been heightened. This scheme isthat we investigate the HHG power spectrum of muonic atominteracting with laser. Because HHG spectrum has no relationwith the specific shape of atomic potential, we propose aone-dimensional muonic atom model, whose potential is a modifiedPoschl-Teller one, in order to simplify the computation. It is ashort-range potential, in which the wavefunctions in all energydomains have exact analytic solutions. In addition, with thispotential we can arbitrarily choose the number of the boundstates by adjusting the parameters of this potential.In this thesis, by using the Crank-Nicolsontime-propagation method, we systematically investigated theHHG power spectrum of the one-dimensional muonic atom model.Through observing this HHG spectrum, we gain three facts as followed:①The cutoff position in this HHG spectrum is identical with the cutofflaw. This shows that the classical simple-man'sdynamics( ωcutoff = Ip +3.2Up ) entirely explains the HHG ofmuonic atom. Here what must be emphasized is that m inUp of e2E0 /(4mω2) is the mass of muon in muonic atom.②Though the harmonic plateau is not very wide, the cutoff ofthe harmonic plateau falls into γ-ray region because thefrequency of laser field is very large. ③We notice that theconversion efficiency of the HHG spectrum is very low.We have analyzed the ionization yield which is the majorfactor influencing conversion efficiency, and found that theionization yield is only 6/1000 when the laser pulse ends. Theionization yield is so low that it is known that the conversionefficiency will not be high. We provide the combined pulses toheighten the ionization yield, and gain the HHG spectrumfrom muonic atom interacting with the combined pulses. Wecompare the HHG power spectrum from muonic atom exposed... |
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