Linear and total intersubband transitions in the step-like GaAs/GaAlAs asymmetric quantum well as dependent on intense laser field

Abstract

In this study, for a step-like GaAs-Ga1-xAlxAs asymmetric quantum well (AQW) the linear and total intersubband optical absorption coefficients and the refractive index changes are calculated as dependent on the intense laser field (ILF) and the right quantum well (RQW) width. Our results show that the location and the magnitude of all absorption coefficients and refractive index changes depend on ILF and the asymmetric parameter (d = L-R/L-L). Also, we showed that both ILF and d provide an important effect on the electronic and optical properties of step-like quantum well, and the changes of the energy levels, the dipole moment matrix elements and the resonant peak values of the absorption coefficients are dependent on the shape of the confinement potential. While for different asymmetric parameters the intersubband absorption spectrum shows blue shift up to the different critical ILF values, this spectrum shows red shift for ILF values greater than certain values. By considering the variation of the energy difference as dependent on the RQW width, for step-like QW the absorption spectrum shows blue or red shift. Especially, step-like QWs are used for producing terahertz radiation from intersubband transitions and they have more tunable structure parameters (the left (right) quantum well width, L-L(L-R), and the confinement potential in the left (right) hand side, V-L(V-R)) with respect to other asymmetric QWs (in the present study we used L-R = L-L/2, L-L, 3L(L)/2 and V-R = 2V(L)/3 values). This case provides a new degree of freedom for controlling the optical properties in quantum wells (QWs). In addition, the nonlinear optics underlying the application of the ILF to asymmetric potential heterostructures becomes a subject of present-day interest. In conclusion: i) The electronic and optical properties of the step-like AQW vary by increasing ILF. ii) ILF leads to major modifications on the shape of the confining potential. iii) The position and the size of all absorption coefficients and refractive index changes depend on ILF and the asymmetric parameter values. iv) The absorption spectrum shows blue or red shift by increasing ILF.