Quantum Cascade Laser — Intersubband Population Inversion

A quantum cascade laser generates light from a single conduction band by chirping the width of a superlattice of coupled quantum wells: electrons tunnel into an upper confined subband, drop to a lower one via an intersubband transition that emits a photon, then get swept out by LO-phonon scattering before the next electron arrives — repeating across dozens of identical periods so one electron can emit many photons. This simulator renders that staircase in 3D and lets you tune well width (photon energy), bias alignment (injection efficiency), lattice temperature (lower-level depopulation rate) and current density (pump rate), solving the steady-state two-level rate equations live to show population inversion ΔN and whether the structure crosses the lasing threshold.