Pan Shaohua

Intersubband Optical Absorption in Semiconductor Superlattices with Complex bases

The third-order nonlinear intersubband optical absorption coefficient within the conduction band of semiconductor superlattices with complex bases have been calculated using the density matrix formalism including intrasubband and intersubband relaxation. The subband dipole moments zij (k) and zii (k) are first studied in superlattices with complex bases including a general coupled-well basis and a general step-well basis. The results show that zij (k) and zii (k) are complicated functions of and strongly depends on the well parameters. The intersubband transition optical absorption coefficient α(Ω, I) is further studied. The numerical illustrations are also given.

Study of the properties of infrared intersubband transition in doped GaAs/AlxGa1-xAs multiple quantum wells

The properties of intersubband transition of GaAs/AlxGa1-xAs multiple quantum wells with various well widths and doped-well concentrations have been studied. Both theoretical and experimental results are in good agreement. For the appropriate well width and higher doping concentration, we directly observed two intersubband absorption peaks from E1 → E2 and E2 → E3 transitions in well. The experimental results and theoretical analysis are given.

BOUND POLARONS IN ASYMMETRIC QUANTUM WELLS IN AN ELECTRIC FIELD

We have proposed the Hamiltonian of a polaron bound to a donor impurity in semiconductor quantum wells (QWs) in the presence of an electric field. The couplings of an electron with the confined bulk-like longitudinal optical (LO) phonons, half-space LO phonons and interface phonons are considered. In particular, the interaction of the impurity with the various phonon modes is also included. We have calculated the ionization energy of a bound polaron in AlxlGa1-xlAs/GaAs/AlxrGa1-xrAs asymmetric and symmetric QWs. Results are obtained as a function of the barrier height (or equivalently of Al concentration x), the well width, the electric field intensities and the position of impurity in the QWs. Our numerical calculations show clearly that the interaction between the impurity and the phonon field plays an important role in screening the Coulomb interaction. It is shown that for a thin well (< 12nm), the cumulative effects of the electron-phonon coupling and the impurity-phonon coupling can contribute appreciably to the donor ionization energy and polarizability.

ELECTROMAGNETICALLY INDUCED FOCUSING IN A Λ-TYPE MEDIUM

Electromagnetically induced transparency (EIT) in an inhomogenously broadened medium consisting of Λ-type three-level atoms has been analyzed. It is shown that the Λ system can induce a transparency of the medium when the probe laser and the coupling laser have the same frequency detunings (including zero). Across the EIT window, the radial variation of the strong coupling laser radiation may lead to electromagnetically induced focusing or defocusing of the weak probe laser at separate probe frequency detuning points.

STUDY ON OPTICAL BISTABILITY OF DYE-RING CAVITY WITH BAND MODEL

Abstract The optical bistability in a dye ring cavity has been investigated.It is shownthat the bistability can be realized in a much wider frequency rilnge,and that thebistable regions are functions of the band structures(the bandwidth and the distri-bution of dipole moments).

Optical Bistability in Semiconductors with Many-body Coulomb Effects

The Bloch-like equations for the intracavity interaction of coherent light with semiconductors below the Mott density are derived. These equations include the many-body Coulomb effects. Steady state analysis reveals the characteristics of bistability and hysteresis in such systems. It is shown that the hysteresis loops increase and that the bistability can be realized more easily due to the many-body effects.

Nonlinear optical effects induced by a z5-type anharmonic potential

Using the density matrix formalism based on the exact wave functions for a parabolic quantum well with applied electric fields, we derive in this paper analytical expressions for nonlinear optical effects of a z5-type anharmonic potential. A numerical illustration is also given. Moreover, we describe in detail the method for obtaining the anharmonic potential in a doping superlattice.

Interface Optical-Phonon Modes in a C/B/A/B/C Five-Layer Heterostructure of Polar Crystals

The equations of motion for the p-polarization field in a C/B/A/B/C-type five-layer heterostructure of polar crystals are solved exactly for the interface optical-phonon modes. The eigenvectors are obtained explicitly. The dispersion relation is derived and discussed in detail for some limiting cases. This work can be regarded as a generalization of the formalism of that of Shi and Pan [Phys. Rev. B46, 4268(1992)].

Electronic Wave Functions and Subband Energies in Superlattice with a Complex Basis

Electronic wave functions and energies in superlattice with a complex basis have been obtained that are more general than those of Pan et al. [Phys. Rev. B 44 (1991) 5668]. This paper gives not only subbands but also wave functions for all values of the wave number for superlattice with a complex basis.

A Universal Value for the Charge-Transfer States of Different Alkali-Halide Molecules

The scaled potentials were used to discuss the vibrational quantum defects of alkali-halide molecules by using the fully quantal Milne equation method and the quasiclassical Wentzell-Kramers-Brillouin approximation. This allowed us to obtain a universal function and its limit value for the charge-transfer states of different alkali-halide molecules.