Laser
Light Amplification by Stimulated Emission of Radiation—a device producing coherent, monochromatic, highly directional, high-intensity light.
Governing formula
E = h ν, Population Inversion N2 > N1
SI unit
W (or J)
In depth
Requires population inversion in an active medium inside a resonant optical cavity. Photons trigger stimulated emission, producing identical phase/wavelength photon cascades.
Examples in the real world
Helium-Neon red lasers, semiconductor laser diodes in barcode scanners, and high-power industrial laser cutters.