Abstract

Laser sources producing nanosecond (10-9 s) to sub-picosecond (10-12 s) pulses (i.e. ultrafast lasers) are deployed in a variety of applications ranging from scientific research, laser surgery, material processing and telecommunications. Regardless of the output wavelength, the majority of ultrafast laser systems employ a mode-locking technique, whereby a nonlinear optical element – called Saturable Absorber (SA) – turns the laser continuous wave output into a train of ultrashort optical pulses. The SA absorption (or optical loss) decreases as the incident light intensity increases. Thus, the SA works as an intensity-dependent optical switch. The key requirements for SAs are fast response time, high modulation depth, broad wavelength range, low optical loss, low-cost and ease of integration into an optical system. Graphene, a one atom thick layer of carbon atoms arranged in a honeycomb lattice, can simultaneously meet all these needs with better performances and lower cost compared to current technologies. In this seminar I will introduce the basic concepts of ultrafast lasers and mode-locking and their importance for technological applications. I will then review the fundamental physical properties that make graphene the ideal candidate as saturable absorber for ultrafast lasers on an extremely broad energy range from visible to THz.