Coherent Transient And Ultrahigh Resolution Transient Measurement With Incoherent Light

The coherent transient is very important in understanding the dynamical behavior of the light-matter interaction . In this paper, the coherent transient in the three-level atom system and ultrahigh resolution transient measurement with incoherent light have been discussed theoretically . The paper is divided into three parts: In the first part , we have investigated a class of coherent transients in a ladder three-level system in the so-called pump-probe configuration , where the time-dependent response of a weak-probe limited field has been studied under a strong pump field . In the second part, ultrahigh resolution coherent transient measurements with incoherent light in the three-level A -like system and coherent control have been investigated . Finally , we have presented a new method of optical heterodyne-detection to study Rayleigy-enhanced transient four wave mixing .Part One:Quantum interference effects which were excited by a strong pump pulse and a weak probe pulse, have been investigated in a ladder three-level atom system systematically. The numerical results using the method of stationary phase shows the interference fringes in spectral , which can accurately predict the amplitudes of the frings . To describe the frings more accurately , we use the simplified treatment that it ignores the time evolution of the energy level. Based on the field-correlation theory, analytic representation of the population of final state was obtained, the character of the fringes such as period and shape can also be predicted accurately. We also describe theoretically the temporal evolution of the excited state population induced by chirped pump pulse , and find that we can control the population by manipulating the chirped pulse.Part Two:A novel approach to measure the spacing of two close energy states with two incoherent light was presented . Based on the principle of field-correlation , we obtained a analytic representation for population of the final state and the numerical results verified the feasibility of this approach . Comparing the results which were got from two defferent modle of the excited field, it was found that accurate measurement in temporal needs very wide laser spectral band , at least a half of the state spacing . If the laser spectral cannot overlap the two close states , exciting the atom at the middle of them is demanded to realize the accurate measurement.It was also found that the population can be controlled by using two time-delayed pulses . When two pulses overlapped completely , the population trap was obtained in two lower states through fixing the relative phase difference between the two pulses at odd times of n. The informations about the life of coherent state can also be gotten from the time evolution of the population in the final state .Part Three:A closed-form solution of the difference-frequency beats and the representation of third-order susceptibility for Rayleigh-enhanced four wave mixing were obtained by the method of optical heterodyne-detection. The numerical results illustrate that the method can keep the information of Rayleigh-enhanced polarization completely. And the physical analysis of the difference based on three Markovian stochastic models were also given in paper.