Nonlinear optical elements for generating ultrashort laser pulses
Graphene has nonlinear optical properties. Namely, when the power density of the incident laser radiation is less than 100 kW per square cm, the graphene monolayer absorbs 2.3% of the intensity of the incident radiation, while with an increase in the density of the incident radiation above 100 kW per square cm in graphene absorption is saturated, and it begins to transmit incident light.
According to the described phenomenon of absorption saturation in graphene, passive nonlinear optical elements work in the formation of ultrashort laser pulses. In other words, the laser goes into self-mode locking regime and pulses with higher peak power and a duration of hundreds of femtoseconds are formed from continuous radiation.
The figure on the left shows a diagram of a fiber laser with a ring resonator. A graphene film is deposited on a fiber section. At the input of the experiment, pulses of a duration of 380 fs were obtained.
Graphene has a number of advantages over existing Semiconductor Saturable Absorber Mirror (SESAM) counterparts.