Patent ID: 7864828

Claim:
A cascade laser device, comprising: a multilayer film structure with a multiple quantum well including a potential barrier and a quantum well; and an electric field applying portion for applying an electric field to the multilayer film structure, wherein the multilayer film structure includes at least two first regions and a second region, the second region being sandwiched between the at least two first regions, wherein each of the at least two first regions includes multiple sub-bands, and, when the electric field is applied, carriers are transported from a sub-band in a higher energy quantum well to a sub-band in a lower energy quantum well via the potential barrier in the at least two first regions by tunneling permitted by interaction with light, and wherein the second region is thinner than twice a skin depth of the light and includes at least a film that is thicker than a de Broglie wavelength of the carriers and that has a continuous energy band, such that the carriers are subjected to energy relaxation in the continuous energy band.