Quantum Coherence Driven By A Standing Wave In Hot Atomic Systems

This thesis for doctorate focuses on the effects of quantum coherence andinterference with a strong coupling field (either a traveling or standing wave field)because the optical properties of an interaction medium can be modified andcontrollable. We generalized the development of atomic coherence effects,especially on phenomena of electromagnetically induced transparency andphotonic band gap. The creative points in this thesis consist of three parts: Firstly,we propose a five-level system to analyze asymmetrical transmitted spectra ofprobe field in traditional three-level Λ-type and ladder-type systems forElectromagnetically induced transparency and photonic band-gap in hot Cs atoms.By controlling the parameters, the asymmetrical absorptions at dressed states areobtained. Secondly, we carried out the experimental observation and theoreticalanalyzing electromagnetically induced photonic bandgaps in two-level systemwith a strong symmetric and two types of asymmetric standing wave (SW) drivingfield. One main band and two sidebands are measured for the transmitted andreflected spectra. Finally, we propose a scheme by applying a tunablestanding-wave (SW) to control various multi-wave mixing processes in a hotfive-level Rb atomic system to realize triple two-photon photonic bandgaps orthree EITT windows. In two two-photon resonant conditions, electromagneticallyinduced triple-photonic bandgaps can be formed at three resonant frequencies ofthree traveling-wave (TW) probe fields. While one probe travelling-wave (TW)field is as strong as the standing-wave field to be a coupling field, triple-bandpasstwo-photon filters or three EITT windows can be obtained.The contents are mainly divided as three parts: 1. We propose two five-level systems to analyze asymmetrical transmittedspectra of probe field in traditional three-level Λ-type and ladder-type systemsfor Electromagnetically induced transparency and photonic band-gap in atomswith a strong coupling field. It is found that many previous theoreticalcalculations for EIT and EIG provide symmetrical transmission at dressedsplitting states with resonant coupling field, but experimental observationsproduced asymmetrical shapes. Here two five-level systems where two additionaladjoining levels close to the middle level in ladder system or upper level in Λsystem are utilized to analyze asymmetrical spectra shapes in experimentalobservations for EIT and photonic band gap in thermal Cs atoms, respectively.Based on the energy levels for experiments, we found that the two neighboringlevels are chosen to satisfy that transitions of the coupling laser to one of the twois inhibited and to the other is admitted. The reasons of asymmetry transmission atdressed splitting states are found to be the asymmetry transmission in three-levelsystem formed by the admitted neighboring level and the two other levels inoriginal three-level system where it is none zero for the frequency detuning of thecoupling field with corresponding transition to the admitted neighboring level. Wesolve density matrix equations for steady-state solutions without the supposingthat all populations are on the ground state as treatment previously in Dopplerinhomogeneous broadenings for hot atoms. The theoretical calculation shows thatinfluence of other further neighboring levels are the same as the two adjoininglevels. The five level systems are the simplest ones to analyze symmetryproperties of transmissions at dressed splitting states. Our simulating results areconformably to the realistic observations.2. We observed and simulated the effects of quantum coherence driven by aSW field in a thermal two-level Cs atomic system. One main band and twosidebands are measured for the transmitted and reflected spectra. We carry outphysical interpretation about the observations in SW-dressed atom picture and employ method of Fourier transformation to solve density-matrix equations forhot two-level system to simulate the experimental results. We analyze thecontribution of co-and counter-propagating coupling components of SW to thetransmission and reflection spectra. The measured optical spectra exhibit theproperties:(1) there exists a main photonic bandgap at resonance (p0) andtwo sidebands located symmetrically around the main band;(2) with the first typeof asymmetric SW (>) drive, the lower powers in–z direction, the smallertransmission and reflection at main bands; the two subbands move towards themain band and finally disappear when much smaller is used and similarphenomena are measured as EIA by a copropagating TW;(3) with the secondtype of asymmetric SW (<) drive, the lower the powers in+z direction, thelarger transmissions and lower reflections at main band; the two subbands stillmove towards the main band and disappear gradually. The simulation results arefound to be consistent with the experimental results.3we use a tunable standing-wave field to induce two-photon coherence effects inan inhomogeneous five-level Rb atomic vapor. It is demonstrated that tripleprobe-photon bandgaps can be induced by quantum coherence effects of thestanding-wave under two-photon resonant conditions for the three probe fields.When the standing-wave field is changed to a traveling wave field, triple-photonelectromagnetically induced transparency phenomena are obtained under the sameconditions for the three probe fields. When one of the three probe field keepsresonance as a second coupling field besides the tunable standing-wave field, twodressed states further split into four dressed states. By keeping two-photonresonance of the other two probes, triple-bandpass two-photon filters can beobtained. Triple EITT (electromagnetically induced tow-photon transparency)windows are obtained if a traveling field replaces the standing wave. Phase shiftsof probe pulses with Gaussian shapes entering at one end of the medium are calculated to show the scheme useful for dispersion compensation for the probesignals.