QCLs utilize a series of quantum wells and barriers to create a staircase-like structure for electrons. When an electron cascades down these energy levels, it emits a photon at each step. This cascading effect is achieved through precise nanofabrication techniques, allowing control over the emission wavelength by adjusting the thickness and composition of the quantum wells and barriers. The emitted photons are then amplified through an optical cavity, resulting in laser emission.
