Coherent laser control in attosecond sum-frequency polarization beats using twin noisy driving fields

Based on the phase-conjugate polarization interference between two-pathway excitations, we obtained an analytic closed form for the second-order or fourth-order Markovian stochastic correlation of the V three-level sum-frequency polarization beat (SFPB) in attosecond scale. Novel interferometric oscillatory behavior is exposed in terms of radiation-radiation, radiation-matter, and matter-matter polarization beats. The phase-coherent control of the light beams in the SFPB is subtle. When the laser has broadband linewidth, the homodyne detected SFPB signal shows resonant-nonresonant cross correlation, a drastic difference for three Markovian stochastic fields, and the autocorrelation of the SFPB exhibits hybrid radiation-matter detuning terahertz damping oscillation. As an attosecond ultrafast modulation process, it can be extended intrinsically to any sum frequency of energy levels. It has been also found that the asymmetric behaviors of the polarization beat signals due to the unbalanced controllable dispersion effects between the two arms of interferometer do not affect the overall accuracy in case using the SFPB to measure the Doppler-free energy-level sum of two excited states.

Tellurium enhanced non-resonant third-order optical nonlinearity in a germano-silicate optical fiber

碲掺杂的高非线性石英光纤

Resonant subband Landau level coupling in symmetric quantum well

Subband structure and depolarization shifts in an ultrahigh mobility GaAs/Al0.24Ga0.76As quantum well are studied using magnetoinfrared spectroscopy via resonant subband Landau level coupling. Resonant couplings between the first and up to the fourth subbands are identified by well-separated antilevel-crossing split resonance, while the hy-lying subbands were identified by the cyclotron resonance linewidth broadening in the literature. In addition, a forbidden intersubband transition (first to third) has been observed. With the precise determination of the subband structure, we find that the depolarization shift can be well described by the semiclassical slab plasma model and the possible origins for the forbidden transition are discussed.

Accurate determination of electronic transition energy of carbon nanotubes from the resonant behavior of radial breathing modes and their overtones

The resonant Raman behavior of the radial breathing modes are very useful to analyze the electronic property of carbon nanotubes. We investigated the resonant behaviors of Stokes and anti-Stokes radial breathing mode and its overtone of a metallic nanotube, and show how to accurately determine the electronic transition energy of carbon nanotubes from radial breathing modes and their overtones. Based on the present results, the previously reported resonant Raman behavior of the radial breathing modes of SWINT bundles can be interpreted very well.

ELECTRON-STATES OF A STACKING-FAULT RIBBON IN SILICON

The electronic structure of a bounded intrinsic stacking fault in silicon is calculated. The method used is an LCAO-scheme (Linear Combinations of Atomic Orbitals) taking ten atomic orbitals of s-, p-, and d-type into account. The levels in the band gap are extracted using Lanczos' algorithm and a continued fraction representation of the local density of states. We find occupied states located up to 0.3 eV above the valence band maximum (E(v)). This significantly differs from the result obtained for the ideal infinite fault for which the interface state is located at E(v)+ 0.1 eV.

COHERENT MODEL FOR RESONANT-TUNNELING OF ELECTRONS IN DOUBLE-QUANTUM WELLS UNDER ELECTRIC-FIELDS

Taking the inhomogenous broadening of the electron energy levels into account, a coherent model of the resonant tunneling (RT) of electrons in double quantum wells is presented. The validity of the model is confirmed with the experiments [M. Nido et al., Proc. SPIE 1268, 177 (1990)], and shows that the tunneling process can be explained by the simple coherent theory even in the presence of the carrier scattering. We have discussed the dependence of resonant tunneling on the barrier thickness L(B) by introducing the contrast ratio LAMBDA and the full width at half depth of the RT valley, and found that LAMBDA first increases with increasing barrier thickness, reaches a maximum, and then decreases with a further increase of L(B), in striking contrast to the Fabry-Perot model where a monotonic increase of the peak-to-valley ratio is predicted. We attribute the reduction of LAMBDA with large L(B) to the energy broadening resulting from the carrier scattering. A monotonic decrease of the full width at half depth of the RT valley with an increase of L(R) is also found.

DENSITY-OF-STATES OF THE 2-DIMENSIONAL ELECTRON-GAS STUDIED BY MAGNETOCAPACITANCES OF BIASED DOUBLE-BARRIER STRUCTURES

The magnetocapacitive response of a double-barrier structure (DBS), biased beyond resonances, has been employed to determine the density of states (DOS) of the two-dimensional electron gas residing in the accumulation layer on the incident side of the DBS. An adequate procedure is developed to compare the model calculation of the magnetocapacitance with the experimental C vs B curves measured at different temperatures and biases. The results show that the fitting is not only self-consistent but also remarkably good even in well-defined quantum Hall regimes. As a result, information about the DOS in strong magnetic fields could reliably be extracted.

ANTICROSSING DUE TO RESONANT COUPLING OF HOLE LEVELS IN ASYMMETRIC COUPLED-QUANTUM-WELLS

We present distinct evidence of anticrossing behavior for excitonic transitions due to resonant coupling of heavy-hole ground levels in a biased GaAs/Al0.35Ga0.65As/GaAs (50/40/100 angstrom) asymmetric coupled-double-quantum-wells p-i-n structure by using photoluminescence spectra. The minimum level splitting is about 2.5 meV.

SELF-CONSISTENT TREATMENT OF 3-DIMENSIONAL - 2-DIMENSIONAL AND 2-DIMENSIONAL - 2-DIMENSIONAL RESONANT-TUNNELING IN DOUBLE-BARRIER STRUCTURES

By using a transfer-matrix method on the basis of two-dimensional (2D) Bloch sums in accordance with a tight-binding scheme, a self-consistent calculation on the resonant tunneling in asymmetric double-barrier structures is presented, in which contributions to resonant tunneling from both three-dimensional (3D) electrons in the contacts and 2D electrons in the spacer or accumulation layers are considered simultaneously. The charge buildup effect on the current versus voltage (I-V) curves is evaluated systematically, showing quantitatively how it results in the I-V bistability and enhanced differences between I-V curves for positive and negative bias in an asymmetric double-barrier structure. Special attention is focused on the interaction between 3D-2D and 2D-2D resonant-tunneling processes, including the suppression of 2D-2D resonant tunneling by the charge buildup in the well accompanying the 3D-2D resonant tunneling. The effects of the emitter doping condition (doping concentration, spacer thickness) on the presence of two types of quasi-2D levels in the emitter accumulation layers, and on the formation of a potential bulge in the emitter region, are discussed in detail in relation to the tunneling process.