Free electron model

About: Free electron model is a research topic. Over the lifetime, 4678 publications have been published within this topic receiving 103535 citations.

Photorefractive quantum wells: Transverse Franz-Keldysh geometry

Abstract: The photorefractive properties of semi-insulating AlGaAs–GaAs multiple quantum wells are described for the transverse Franz–Keldysh geometry with the electric field in the plane of the quantum wells. Combining the strong electroabsorption of quantum-confined excitons with the high resistivity of semi-insulating quantum wells yields large nonlinear optical sensitivities. The photorefractive quantum wells have effective nonlinear optical sensitivities of n2 ≈ 103 cm2/W and α2/α0 ≈ 104 cm2/W for applied fields of 10 kV/cm. Photorefractive gains approaching 1000 cm−1 have been observed in two-wave mixing under dc electric fields and stationary fringes. The transverse Franz–Keldysh geometry retains the general transport properties and behavior of conventional bulk photorefractive materials. The resonant excitation of free electrons and holes in the quantum wells leads to novel behavior associated with electron–hole competition. We demonstrate that under resonant excitation of electrons and holes the device resolution is fundamentally limited by diffusion lengths but is insensitive to long drift lengths.

Theory of free-electron lasers

Abstract: Abstract : A general analysis is presented of free electron lasers in which a static periodic magnetic pump field is scattered from a relativistic electron beam. The steady state formulation of the problem is fully relativistic and contains beam thermal effects. Growth rates associated with the radiation field, efficiencies, and saturated field amplitudes are derived for various modes of operation. Effects of space charge on the scattering process are included and shown to play a dominant role in certain situations. Scaling laws for the growth rates and efficiencies at a fixed radiation frequency as a function of the magnetic pump amplitude are obtained. The shear in beam axial velocity due to self fields is discussed and various methods of reducing it are suggested. Finally, a detailed illustration of a far infrared (lambda = 2mu m) two-stage free electron laser using a 3 MeV electron beam and a 2 cm wavelength magnetic pump field is presented.

Magnetic g factor of electrons in GaAs/AlxGa1-xAs quantum wells.

Abstract: The magnitude and sign of the effective magnetic splitting factor g* for conduction electrons in GaAs/AlxGa(1-x)As quantum wells have been determined as a function of well width down to 5 nm. The experimental method is based on combined measurements of the decay time of photoluminescence and of the suppression of its circular polarization under polarized optical pumping in a magnetic field perpendicular to the growth axis (Hanle effect). Measurements as a function of hole sheet density in the wells reveal a transition from excitonic behavior with very small apparent g value for low density, to larger absolute values characteristic of free electrons at higher densities. For 20-nm wells g* for electrons is close to the bulk value (-0.44), and increases for narrower wells passing through zero for well width close to 5.5 nm. A theoretical analysis based on three-band k.p theory, including allowance for conduction-band nonparabolicity and for wave-function penetration into the barriers, gives a reasonable representation of the data, leading to the conclusion that g* in quantum wells has a value close to that of electrons in the bulk at the confinement energy above the band minimum.

Band Formation from Coupled Quantum Dots Formed by a Nanoporous Network on a Copper Surface

Abstract: The properties of crystalline solids can to a large extent be derived from the scale and dimensionality of periodic arrays of coupled quantum systems such as atoms and molecules. Periodic quantum confinement in two dimensions has been elusive on surfaces, mainly because of the challenge to produce regular nanopatterned structures that can trap electronic states. We report that the two-dimensional free electron gas of the Cu(111) surface state can be trapped within the pores of an organic nanoporous network, which can be regarded as a regular array of quantum dots. Moreover, a shallow dispersive electronic band structure is formed, which is indicative of electronic coupling between neighboring pore states.

Nonsequential double ionization of helium

Abstract: Electron correlation effects in strong laser fields are investigated by using a simplified two electron model to calculate the double ionization rate in helium. In our model we make a correction to the single active electron approximation by including the effect of the outer electron on the inner one through a time-dependent potential. Using this approach we are able to investigate the nonsequential double ionization observed in recent experiments. {copyright} {ital 1997} {ital The American Physical Society}