Optical sideband generation up to room temperature with mid-infrared quantum cascade lasers

Giant optical nonlinearity interferences in quantum structures

“…The second-order nonlinearity is thus doubly enhanced, permitting efficient sideband generation on an optical carrier (ENIR ± EQCL) [5]. Recently it has been shown that quantum cascade lasers (QCLs) can be used as both the source for THz and midinfrared (MIR) radiation (and intersubband excitation) and the nonlinear medium with an external NIR excitation coupled into the QCL cavity [14][15][16][17][18]. (QCLs exploit intersubband electronic transitions that enable laser action in the THz and MIR regions of the electromagnetic spectrum).…”

“…This can only probe the lowest lying interband states as the absorption strongly increases with the interband energy: it simultaneously severely reduces the region where SFG occurs to a very small part of the cavity and suppresses its propagation along the cavity towards the opposite side (absorption length is typically a few microns whereas the cavity is a few millimeters). [14,15,17,18].…”