The dispersion behaviors of the tripod-type four-level cylindrical quantum dot under phenomenon of electromagnetically induced transparency

In this paper, linear and 3rd-order nonlinear group velocities of the probe laser field are investigated in a tripod-type four-level cylindrical quantum dot (TTFLCQD) with parabolic potential in electromagnetically induced transparency. The nonlinear refractive index for this system is calculated by obtaining the real part of the 1st and 3rd-order susceptibilities. Afterward, linear and 3rd-order nonlinear group velocities are found. The control lasers at z-polarization are applied to the system in order to investigate the linear and 3rd-order nonlinear group velocities and the results are discussed. The linear and 3rd-order nonlinear group velocities are compared at z-polarization. Furthermore, the effects of parameters of TTFLCQD and control lasers on linear and 3rd-order nonlinear group velocities are explored. Finally, 3rd-order nonlinear group velocity for z- and x-polarization is compared.