Nonlinear intersubband terahertz absorption in asymmetric quantum well structures

The THz nonlinear absorption of asymmetric double quantum wells is calculated. The dependence of the absorption on different parameters of the quantum wells is studied. In particular, different values of the barrier and wells width are considered. Also, a dc field in the direction of growth of the wells is introduced in the calculations and the nonlinear absorption is obtained for different dc and ac field intensities. The nonlinear absorption is obtained by using a perturbation calculation of the nonlinear susceptibility up to the third order within a density matrix approach. The absorption spectra are studied near the anticrossing of the first two excited subbands. Special attention is given to the nonlinear peaks due to the intensities of both fields. In particular some interesting negative nonlinear peaks are found and their dependence on the intensities of the fields is discussed.

Figure 1

Potential profile of an ADQW (Ref. 16).

Figure 2

Eigenenergies of the ADQW vs $W_2$ without external electric field for $B=60\mathrm{\AA }$ (Ref. 17).

Figure 3

(Color online) Energy gap vs $B$ without external electric field (Ref. 18).

Figure 4

(Color online) Linear absorption of the ADQW with $B=20\mathrm{\AA }$ vs $W_2$ without external electric field (Ref. 19).

Figure 5

(Color online) Absorption of the ADQW with $B=60\mathrm{\AA }$ vs $W_2$ without external electric field (Ref. 20).

Figure 6

(Color online) Nonlinear Absorption of the ADQW with $B=20\mathrm{\AA }$ vs $W_2$ with external radiation $E=5\mathrm{kV}∕\mathrm{cm}$ (Ref. 21).

Figure 7

Eigenenergies of the ADQW vs $F$ without external electric field for $W_2=38\mathrm{\AA }$ (Ref. 22).

Figure 8

(Color online) Energy gap vs $F$ (Ref. 23).

Figure 9

(Color online) Nonlinear absorption vs $W_2$ with external electric field $(F=4\mathrm{kV}∕\mathrm{cm})$ for several barrier and radiation values (a) $E=0.1\mathrm{kV}∕\mathrm{cm}$, $B=20\mathrm{\AA }$; (b) $E=0.5\mathrm{kV}∕\mathrm{cm}$, $B=20\mathrm{\AA }$; (c) $E=0.5\mathrm{kV}∕\mathrm{cm}$, $B=40\mathrm{\AA }$; and (d) $E=3\mathrm{kV}∕\mathrm{cm}$, $B=40\mathrm{\AA }$ (Ref. 24).

Figure 10

Nonlinear absorption with $B=20\mathrm{\AA }$ for two cases (a) $F=8\mathrm{kV}∕\mathrm{cm}$, $E=0.5\mathrm{kV}∕\mathrm{cm}$ and $W_2=26\mathrm{\AA }$, (b) $F=12\mathrm{kV}∕\mathrm{cm}$, $E=1.0\mathrm{kV}∕\mathrm{cm}$, and $W_2=37\mathrm{\AA }$ (Ref. 26).