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 Schrodinger 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, wher...

Unexpected transition from single to double quantum well potential induced by intense laser fields in a semiconductor quantum well

We present a review of the recent progress in the generation methods of intense terahertz (THz) single-cycle pulses and their application to THz nonlinear spectroscopy in condensed matters. Special attentions are paid to various aspects of nonlinearity in semiconductors including dynamical Franz-Keldysh effect, ballistic acceleration of free carriers, and coherent control of the exciton system.

THz Nonlinear Spectroscopy of Solids

Intense laser field effects on the linear and nonlinear optical properties in a semiconductor quantum wire with triangle cross section

A systematic study on the influence of two intense, long-wavelength, nonresonant laser fields on the electron energy levels and density of states (DOS) in $\mathrm{GaAs}∕\mathrm{AlGaAs}$ quantum wells is performed within a Green's function approach. The carrier confinement pattern and its associated DOS are shown to be modified by the laser beams. For laser field polarizations parallel to the growth direction only the effective potential is changed whereas for in-plane polarizations only the DOS is altered in the sense that it is field-driven. The results show that for a $\mathrm{GaAs}∕\mathrm{AlGaAs}$ quantum well the effect of the laser field radiation is to induce strong blueshifts in the electronic energy levels. The DOS dependence on the laser-induced confinement characteristics changes from the usual ladder profile to a functional form that reminds us of a one-dimensional system.

Electronic properties of a quasi-two-dimensional electron gas in semiconductor quantum wells under intense laser fields

The simultaneous influences of an intense laser field and static electric field on one-electron states and intraband optical absorption coefficient are investigated in two-dimensional GaAs/GaAl0.3 As quantum ring. An analytical expression of the effective confining potential in the presence of the external fields is obtained. The one-electron energy levels and wave functions are calculated using the effective mass approximation and an exact diagonalization technique. We show that changes in the incident light polarization lead to blue- or redshifts in the intraband optical absorption spectrum. Moreover, we found that blueshift and redshift are induced by the simultaneous influences of an intense laser and lateral electric fields. The obtained theoretical results indicate a novel opportunity to tune the performance of quantum rings and to control their specific properties by means of intense laser and homogeneous electric fields.

http://iopscience.iop.org/article/10.1088/0268-1242/30/4/045006/pdf

The effects of the intense laser and homogeneous electric fields on the electronic and intraband optical properties of a GaAs/Ga0.7 Al0.3As quantum ring

Band-gap luminescence from a variety of compound semiconductors has been observed under intense mid-infra-red irradiation by the free electron laser (FEL) at the Institute of Free Electron Laser, Osaka University. The FEL wavelength and power dependences of the FEL-induced luminescence intensity were measured, and the results are compared with those obtained by a full-band Monte Carlo simulation.

T. Takahashi

Papers

Study of electron-hole generation and recombination in semiconductors using the Osaka free electron laser