Study On Several New All Solid-state Mode-locked Lasers

Ultrafast lasers have great value in scientific research, industry, medical applications due to its dramatic short pulse width and broad-band spectrum. As the major technique to generate ultrafast lasers, the developments of mode-locking have gained more and more attention. The emergence of increasingly new materials makes breakthroughs in output power, pulse width, repetition rate, cost and universality. In this thesis, several mode-locked solid-state lasers were studied at the background of new optical modulation devices. It is put forward that using dual-SESAM system to overcome the disadvantages of single-SESAM, which is sensitive to the performance of the only SESAM. Using two SESAMs in one cavity,50 h ongoing mode-locked pulse was obtained with an average output power of 2.4 W and a pulse width of 10 ps.The dual-SESAM system was proved to be more stable than the cases with single SESAM. The experimental results provide promising way for industrial applications (Chapter 2). Due to inhomogeneous broadening, multi-peak structure was observed in the fluorescence spectra of Nd:LGGG and Nd:SYSO, which is in favor of dual-wavelength operation. Synchronous mode-locked laser pulses were achieved in these two crystals separately. Two wavelengths were simultaneous mode-locked at 1060.9 and 1062.7 nm for NdrLGGG and three wavelengths at 1075.55,1076.80 and 1078.20 nm for NdrSYSO. Their spectrums were analyzed as well as autocorrelation traces. Multi-wavelength synchronous mode-locked lasers have potential application in coherent terahertz (THz) radiation (Chapter 3).2 μm lasers have large absorption coefficients in water and it also corresponds to the eye-safe region. Tm and Ho are the main dopant ions operating in the near infrared around 2 μm. Adopting a Tm:YAP crystal as the gain medium, which has large emission cross section,710mW,1.94 μm, 1.89ps mode-locked pulse was demonstrated by carefully calculating the mode radii on the SESAM (Chapter 4). The results above reveals advantages SESAMs possess, which is stable, reliable, and easy to use. But they also have intrinsic drawbacks, such as complex growth techniques, high cost and narrow absorption wavelength range. The discovery of graphene paves the way of 2D new saturable absorbers. New 2D materials, including graphene, transition metal sulfide, and black phosphorus and so on, are provided with fantastic optical and electrical properties. They have simple fabrication process, controllable bandgap, short relaxation time and broad absorption .band. This article theoretically analyzed the bandgap structure and the mechanism of saturable absorption in 2D materials. And experimentally realized 1.3 μm mode-locked pulse based on controllable absorption graphene, GHz pulse by MoS2/graphene heterostructure, and femto-second pulse using WS2 nanosheets.