Absorption saturation of intersubband optical transitions in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum wells

The optical-absorption saturation of intersubband transition within the conduction band of GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum wells (MQW’s) has been investigated. The MQW sample grown by molecular-beam epitaxy consists of 50 periods of 70-Å-wide GaAs wells and 178-Å-wide ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As barriers with x=0.25. The absorption is peaked at 9.49 μm. The infrared radiation from a tunable transversely excited atmosphere ${\mathrm{CO}}_2$ laser was to induce the transition between the lower subbands. The saturation intensity obtained is ${\mathit{I}}_{\mathit{s}}$=0.67 MW/${\mathrm{cm}}^2$. Using our theoretical expression for saturation intensity, we have calculated ${\mathit{I}}_{\mathit{s}}$=0.52 MW/${\mathrm{cm}}^2$.