To make a mirrorless laser

摘要

Inside any laser is a cavity with a "gain medium" that gives the laser its energy to emit light. A typical gain medium contains atoms that can be excited by using an external energy source and is sandwiched between a pair of mirrors. The mirrors impose a periodicity on the light inside the cavity-similar to how the length of a guitar string limits what musical notes can be played-and allows the medium to pack more energy into the light each time it passes through the gain medium. On page 425 of this issue, Lyubarov et al. (1) propose a radically new approach to making a laser in which the cavity is replaced by a medium with no mirrors. Instead, the optical properties of the medium are periodically modulated in time.