Passive mode locking of lasers by inserting saturable absorbers is commonly used to achieve emission of ultra-short pulses. This operation mode is favored by the laser when it experiences reduced absorption losses for high-intensity pulses compared to continuous-wave operation.
The Semiconductor Saturable Absorber Mirror (SESAM) is the perfect device to introduce these saturable losses. By using quantum wells or quantum dots as absorber material in a specifically adapted semiconductor structure, its properties can be tailored to the laser gain medium and the cavity design to achieve the optimal performance.