Quantum Cascade Lasers: New Light Sources for the Mid-to-Far-Infrared

Quantum cascade lasers are new unipolar light sources based on electron resonant tunneling and optical transitions between quantized conduction band states. Quantum engineering of the electronic energy levels, wavefunctions, matrix elements and scattering rates is used to design population inversion and optimize laser gain and overall performance. Their wavelength can be selected over a broad range of the infrared spectrum using the same heterostructure material by tailoring the active layer thickness. High power room temperature operation at 5 and 8.5 ¿m has been achieved. These are the first semiconductor lasers to operate at 300 K and above in this wavelength region.