When an electronic system is irradiated by an intense laser field, the potential “seen” by electrons is modified, which affects significantly the bound-state energy levels, a feature that has been observed in transition energy experiments. For lasers for which the dipole approximation applies, a nonperturbative approach based upon the Kramers–Henneberger translation transformation, followed by Floquet series expansions, yields, for sufficiently high frequencies, the so-called “laser-dressed” potential, which is taken for composing a time-independent Schrödinger equation whose solutions are the desired quasistationary states. This approach, developed originally for atoms, has been verified to be useful also for carriers in semiconductor nanostructures under intense laser fields. In quantum wells, analytical expressions for the dressed potential have been proposed in literature for a nonresonant, intense laser field polarized perpendicularly to the interfaces. By noting that they apply only for α0≤L/2, where α0 is the laser-dressing parameter and L is the well width, we derive here an analytical expression valid for all values of α0. Interestingly, our model predicts the formation of a double-well potential for laser frequencies and intensities such that α0>L/2, which creates a possibility of generating resonant states into the channel. In addition, the rapid coalescence of the energy levels with the increase in α0 we found indicates the possibility of controlling the population inversion in quantum well lasers operating in the optical pumping scheme.

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Calculations of the binding energy of an on-center donor hydrogenic impurity in a quasizero-dimensional quantum-well system [quantum dot (QD)] placed in an intense, high-frequency laser field are presented. A nonperturbative theory and a variational approach are used as the framework for this calculation. The effect of the intense laser field is to “dress” the impurity potential making it dependent upon the laser field amplitude. A rapid decrease of the binding energy, for different values of the QD radius and for both infinite and finite potential barriers, with increasing field intensity is predicted. An application is made for a spherical QD made of GaAs/Ga1−xAlxAs heterostructures.

We study the behavior of excitons in a semiconductor irradiated by a monochromatic, linearly polarized, intense laser field. By taking the finiteness of the hole effective mass into account and including the radiation field in a semiclassical manner, we solved the two-body quantum problem in the framework of a nonperturbative theory based upon the Kramers-Henneberger translation transformation for the Schrödinger equation. In the Kramers frame, the rapidly oscillating potential is expanded in a Fourier-Floquet series and, for laser frequencies high enough, only the zeroth-order term survives, the so-called “laser-dressed” potential. By applying the Ehlotzky’s approximation, this potential simplifies to a two-center potential that resembles that for the electronic motion in the H2+ molecule ion. The binding energy for an exciton in bulk GaAs under a nonresonant laser field is then computed by following a variational scheme we recently adapted from the linear combination of atomic orbitals-molecular orbitals method for the H2+ system. Similarly to the binding energy in H2+ in the separated-atoms limit, we found that, instead of vanishing, the exciton binding energy tends to a quarter of the excitonic Rydberg energy with the increase of the laser intensity. We also trace a correlation between this residual binding and the dichotomy of the excitonic wave function in the large dressing parameter limit, which indicates the possibility of excitons becoming stable against ionization.

The advent of lasers created entirely new possibilities for the study of the interaction of intense fields with solids. These strong fields can reduce energy gaps [l, 21, distort optical absorption edges [3], shift critical temperatures of magnetic solids [4, 51, change phonon and magnon damping coefficients [6 to 81, etc. Another new and interesting intense field effect we bring about in this note is that of the changes induced by an intense high-frequency radiation field in the binding energy of a bound electron in a solid, e.g. an impurity in a semiconductor.The system we are interested in is a substitutional impurity in a semiconductor. In such circumstances either a shallow or deep level appears. In order to avoid problems with the description of the wave function for deep levels we will restrict our analyses only to shallow traps.The problem of the description of a shallow level impurity whose electron is loosely bound to the charged impurity ion, can be simplified to that of a hydrogenic atom in a dielectric medium where the mass of the bound electron is the effective mass of the free electron in the associated band. The result of the full quantum mechanical treatment gives the following equation of motion for the impurity electron [9]:[ 2m* h2 ( 3 1 F(r) represents an envelope function, which modulates the rapidly varying part of the total wave function, in this case a Bloch function. The impurity potential is reduced in the solid by a factor of dielectric constant c. The complete wave function, in general, is written in the form In other words, the Bloch function unK(r) to be taken into account is that of the nearest band where the impurity sits. The solution of (1) gives the allowed energy levels of the bound electron as where En is the energy of the levels measured relative to the band edge, m* is the electron effective mass, E the dielectric constant, and R, the Rydberg constant.') P.O. Box 04629, 70910-900 Brasilia-DF, Brazil.