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

Abstract

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. © 2009 American Institute of Physics.