Development, Features and Applications

industry, medicine and other areas of contemporary life. The essential ingredients of a laser are a material that amplifies light through stimulated emission (the gain medium) and a cavity that traps light in the gain medium to enable more efficient amplification. The gain medium is pumped electrically, by a source current, or optically, by another laser source or a lamp. The most common laser cavity is the Fabry-Pérot, made of two mirrors (one of which is partially transmitting) that face each other on either side of the gain medium [Fig. 1(a)]. Light that is bounced back and forth between the mirrors is amplified each time it passes through the gain medium. Light can leave the cavity through the partially transmitting mirror. Light that remains in the cavity interferes constructively after traveling a round trip between the mirrors and returning to its (Above) Alexey Yamilov (left) and graduate students Wei Fang and Xiaohua Wu carry out optical measurements of random lasers in professor Hui Cao’s (right) laboratory at Northwestern.