Ansheng Liu

Nonlocal theory of the intersubband optical Kerr effect in a semiconductor quantum well

Taking as a starting point the Liouville equation for the one-body density matrix operator, a general expression for the third-order nonlinear current density responsible for the optical Kerr effect associated with intersubband transitions in a quantum well is derived by use of the perturbative expansion method. The nonlinear current density is related to the local field inside the quantum well via a nonlocal relation. By combining the field-induced nonlinear part of the current density with the Maxwell equation, a nonlinear integral equation for the local field is established. For a two-level quantum well, the integral equation is solved exactly. The nonlinear optical reflectivity, transmittance, and absorbance of the quantum well in turn are obtained. Numerical calculations of the light-induced change of the optical spectra are presented for a Al0.5Ga0.5As/GaAs/Al0.5Ga0.5 As quantum well. The numerical results show that the optical reflectivity and absorbance decrease, and the transmittance increases as the optical intensity of the incident light is increased. In the case where the quantum-well structure is heavily doped, a notable light-induced red-shift of the location of the resonance peak in the optical spectra stemming from the combined local-field effect and field-induced population redistribution is predicted.

Local-field-resonant optical paramagnetic response of a metallic quantum well

Abstract A self-consistent scattering-theory formalism for the optical paramagnetic response is used to study the p-polarized local field inside a metallic quantum well. The energy reflection, transmission and absorption spectra are calculated for a superthin niobium film embedded in quartz, and it is shown that only a single local-field resonance exists.

Optical diamagnetic response of a niobium quantum well

Abstract Reflection spectra of spectra of superthin niobium films deposited on crystalline quartz recently measured by Alieva et al. are interpreted as being due to an optical diagmagnetic response of a niobium quantum well. Based on a selfconsistent local-field calculations spolarized reflection coefficients are determined as a function of frequency and film thickness and compared to the data of Alieva et al.

Quantum-well-number dependence of optical second-harmonic generation in multiple-step quantum wells

Abstract On the basis of a microscopic local-field formalism, optical second-harmonic (SH) generation arising from intersubband transitions in a multiple-step quantum-well (MSQW) structure is investigated theoretically. In an internal reflection configuration the SH energy reflection coefficient as a function of the frequency and the number of quantum wells is calculated for a near-double-resonant GaAs AlGaAs MSQW structure. The numerical results show that the quantum-well-number dependence of the SH conversion efficiency exhibits a pronouncedly oscillatory behavior. This phenomenon is ascribed to the electromagnetic coupling among quantum wells in the MSQW structure.

Characterization of the linear optical properties of a multiple quantum well structure in the sheet-model approximation

Abstract The possibility of determining the linear optical response tensor of a multiple quantum well (MQW) structure from optical reflection spectra is discussed. Taking into account local-field effects, the optical parameters of the MQW system are derived directly from the sheet conductivity tensor of the individual quantum well. For an amorphous Si/SiO 2 MQW structure deposited on a crystalline Si substrate, both s- and p-polarized reflection spectra were measured at different angles of incidence in the near-infrared and visible frequency regions. It was shown that the s-polarized spectra can be characterized by means of only one (complex) parameter, whereas in general it is impossible to account for the p-polarized spectra parametrically in a full range of angles of incidence even with four angular independent parameters. Finally, it was demonstrated that Feibelmans d -parameters can only be used to describe the experimental spectra at near-normal and grazing angles of incidence.

Thickness dependence of optical second-harmonic generation from ultrathin niobium films

Abstract The optical second-harmonic generation from ultrathin niobium films embedded in a dielectric is measured as a function of the film thickness (in the range 6–42 A) for the p ω -to- p 2 ω and s ω -to- p 2 ω polarization configurations. Using a pump wavelength of 532 nm, it is found that the p ω -to- p 2 ω second-harmonic intensity exhibits a pronounced maximum for a film thickness of ∼ 15 A. The s ω -to- p 2 ω second-harmonic signal exhibits a step-like increase at the same thickness. By modeling the metal film as a symmetric quantum well, a microscopic local-field calculation of the second-harmonic generation is established, and numerical results for the thickness and angular dependencies of the second-harmonic energy reflection coefficient are presented. Using simply infinite-barrier wave functions together with a self-field approximation the theoretical calculation qualitatively accounts for the observed thickness dependence of the second-harmonic generation.

Optical bistability due to local-field effects in a single semiconductor quantum well

Using a microscopic nonlocal formalism the optical bistable response of a single semiconductor quantum well is investigated. Starting with a self-consistent nonlinear integral equation for the local field, optical reflection, transmission, and absorption coefficients of the quantum well in connection with intersubband transitions are calculated. In the case where the quantum-well system possesses a low damping, we demonstrate the existence of the intrinsic optical bistability in the quantum well due to the sharp local-field resonance associated with the intersubband transition.

Local-field calculation of the optical paramagnetic response inside a two-level quantum well

A local-field formalism recently developed to describe the optical response of mesoscopic media is used to calculate the linear optical paramagnetic response of a two-level quantum well. Analytical results are presented for the s- and p-polarized components of the local field inside the quantum well. The exact results are compared to those obtained on the basis of the self-field, the first Born, and the so-called self-field first Born approximations. To illustrate our main findings, detailed numerical results are presented for the semiconducting AlGaAs/GaAs/AlGaAs quantum-well system.

Optical diamagnetic response of a niobium quantum well: p-polarized reflection coefficient

Abstract On the basis of a self-consistent local-field calculation, the p-polarized reflection coefficient of a niobium quantum well deposited on crystalline quartz is determined as a function of frequency and well width. It is demonstrated that the local field induced along the quantum well drives the infrared response.

Electromagnetic surface waves on a free-electron-like medium in the presence of a DC current: the dispersion relation

Abstract Within the framework of the so-called semiclassical infinite-barrier (SCIB) model, a non-local dispersion relation for electromagnetic surface waves (SEWs) on a free-electron-like medium in which a DC current is flowing is established. When the drift velocity of the carriers has a non-zero component along an axis perpendicular to the plane of propagation of the SEWs, our new dispersion relation predicts the existence of surface waves with a mixed state of s- and p-polarizations. Limiting ourselves to the hydrodynamic approximation, which allows the presence of collective excitations in the electron gas only, and to the case where the drift velocity is parallel to the propagation direction of the surface waves, we have carried out an elaborated study of the p-polarized SEW dispersion relation. A numerical calculation of the six branches of the dispersion relation has been carried out for n-InSb. Our calculations show that the “local” surface polaritons and the “electrostatic” surface plasmons in the presence of the DC current interact in the frequency regime ω p ϵ ∞ (ϵ ∞ + 1) lsim; ω ≲ ω p ϵ ∞ (ϵ ∞ − 1) . Significant modifications relation are found including new connections of branches. For certain frequencies the dispersion relation obtained predicts the existence of SEW instabilities.