Quantum Coherent Control Of Ionization Photoelectron Spectra With Various Excitation Mechanism

The interaction between light and atoms or molecular has attracted much attention since laser was invented. The primary goal of quantum coherent control is to steer a quantum system selectively towards a desired final state through its interaction with light, while canceling out other paths leading to undesirable outcomes. Quantum coherent control is achieved by controlling the quantum interference among different quantum paths that reach the same final state, which is carried out through operating the coherent characteristics of excited fields. In recent years, with the advent and development of pulse shaping technique, the amplitude, frequency, phase, area of the pulse and/or inter-pulse separation can be controlled accurately to achieve more precise quantum control. The paper is mostly divided into three parts. In the first part, the formulation of two-level atom systems under the dressed state picture and quantum interference effects are investigated. In the second part, quantum coherent modulations on photoelectron in a two resonant multi-photon ionization process are studied theoretically. Finally, properties of ionization photoelectron spectra in a two-photon ionization process which is excited with a frequency-modulated field are discussed in detail.Part One:The transition processes in two-level system are investigated under dressed state picture. Theoretical description from the point of quantum interference is presented clearly to formulate some physical phenomena in two-level system, such asπpulse, population complete transfer, et al. The area of the excited pulse is played important phase factor role in effect of quantum interference. The control function by different light field is formulated in the description. The physical image of some effect and phenomena is presented very clearly by those results.Part Two:The properties of photoelectron spectra in a two resonant excitation multi-photon ionization process are studied with excitation and ionization scheme. The probability amplitudes of various states are obtained analytically by means of dressed state theory and the same method treated in photon echoes. In order to populate the system particles on different dressed states, we obtain the conditions which the first pulse area and the delay time between the two pulses must be contented. Since the coupling of the excited state to the ionization continuum is much smaller than the coupling to the ground state, properties of photoelectron spectra ionized by multi-photon are treated using perturbation theory in the weak-field limit. It is shown that multi-photon ionization photoelectron spectra can be modulated by the areas of the two excited pulses and the delay time between the two pulses. The selective population of dressed states (SPODS) can be implemented using control of the first pulse area and the delay time between the two pulses. Control of the quantum process is achieved based on SPODS. The results we have obtained above are particularly attractive for applications to control the outcome of a chemical reaction with light in physical chemistry.Part Three:Frequency-modulated field whose carrier frequency is fluctuant with a central frequency can be used to achieve population trapping. It has very important application in the fields ranged from isotope separation with laser, single atom detection to molecular state-state reaction and so on. Based on quantum interference effect, the influences on two photon ionization photoelectron spectra with a sinusoidal frequency-modulated pulse are investigated in this part. The effects on two photon ionization photoelectron spectra by modulated amplitude, modulated frequency, initial phase and the detuning are discussed in detail. Mechanism of quantum coherent control in this system is based on the selective population of dressed states (SPODS).