| Nowadays,ultrafast?femtosecond or picosecond?pulse lasers are becoming increasingly popular for various industrial precision process,laser surgery,laser communication,military and science research applications.And ultrafast lasers and related devices are rapidly evolving toward low cost and high performance.Then,it is of great significance to explore new all solid-state ultrafast lasers and various related nonlinear optical?NLO?device with lower cost and higher performance.In the last few years,as important NLO devices for the development and application of ultrafast lasers,some new saturable absorbers and optical limiters based on two-dimensional?2D?nanomaterials have become a hot research topic.Compared with traditional NLO materials,2D nanomaterials such as graphene and transition metal dichalcogenides?TMDs?have the advantages of low cost,simple preparation process and wide working range?covering ultraviolet to infrared band?,and have great application potential as new ultrafast NLO devices.Under above background,this paper focuses on the saturable absorption characteristics of the WS2 2D nano-films and the ultrafast optical limiting properties of the few-layer Mo S2/PMMA composite bulks.Besides,theoretical and experimental study on Yb:KGW all solid-state new ultrafast lasers with high beam quality is also carried out.The main works of this thesis are summarized as follows:1.We have successfully demonstrated a method of greatly modifying the nonlinear saturable absorption?SA?properties of WS2 nanofilms by controlling their thickness and morphology via magnetron sputtering deposition times.The nonlinear SA properties of these nanofilms were also investigated systematically under excitation by laser pulses with various durations in the fs,ps and ns ranges,and prominent ultrafast SA parameters were demonstrated for different pulse durations in the fs,ps and ns ranges.A pulse width-dependent theoretical model of SA that considers the effects of interband exciton recombination has now been proposed for the first time.Two analytical expressions for calculating the variation of key SA parameters?the onset fluence Fon and the modulation depth ?T?with the excitation laser pulse width have been derived and experimentally verified.The theoretical model and analytical expressions have great value for understanding and interpreting the variation of the SA behaviors of 2D nanofilms in the fs,ps and ns regions,and for the developments of ultrafast lasers and nanosecond lasers based on 2D materials.These studies open up exciting avenues for engineering the SA properties of 2D nanofilms for a wide range of laser photonic devices and applications.2.MoS2/PMMA composite bulks have been successfully fabricated by homogeneously incorporating 2D layered Mo S2 nanosheets into solid-state PMMA.The ultrafast nonlinear optical?NLO?properties of these Mo S2/PMMA composite bulks excited by 800 nm ultrafast laser sources in the picosecond?ps?or femtosecond?fs?domains were investigated systematically for the first time.The dependences of optical-limiting performance with respect to the Mo S2 concentration in the samples and the excitation pulse duration were studied in detail.It was found that the optical-limiting response increases with the concentration of Mo S2 nanosheets in the PMMA matrix,and decreases with the excitation pulse duration respectively.The optical-limiting response under 100 fs excitation was much stronger than that under 10 ps excitation pulse.For excitation by 100 fs laser pulses,the Mo S2/PMMA composite exhibits an optical limiting starting threshold of 21.5 m J cm-2,an optical limiting threshold of 315.1 m J cm-2,and a limiting differential transmittance of 1.6% respectively,and these values,to our best knowledge,are lower than those of other bulk nanomaterials,such as Fe2O3,C60,or Se doped silica xerogel,reported previously under the similar transmittance level?85%?.These results have opened the door for highly efficient 2Ddichalcogenides/PMMA composite based optical limiters for ultrafast laser pulses,and have great practical significance for the manufacture of high-quality solid-state optical limiters with low optical loss,high reliability and low cost.3.Analytical expressions for mutually compensating the curved mirror astigmatism in the two terminal arms of a folded resonator are deduced and experimentally verified.The analytical expressions are derived using the theory of the propagation and transformation of Gaussian beams under few assumptions.Our exact analytical expressions describe the necessary and sufficient conditions for simultaneously compensating astigmatism in two arms of a sequence of two off-axis curved mirrors.The theoretical results indicate that when the astigmatism compensation expressions are satisfied,the astigmatism introduced by a folded curved mirror can be mutually compensated by another folded curved mirror even if there is no additional Brewster element inside the cavity.The astigmatism can only be successfully eliminated by using a pair of concave mirrors or convex mirrors.Our analytical expressions can be used to design astigmatically compensated folded resonators without Brewster element.A typical side-pumped z-shaped cavity Nd:YAG laser is employed to demonstrate the astigmatic compensation.Experimental measurements of the pattern of the laser output beam show that not only the spot intensity profiles deformation but also the phase distortion in the two terminal arms can be simultaneously compensated completely in the cavity,which is in good agreement with the analytical predictions.4.All solid-state Yb:KGW ultrashort pulse laser with high beam quality and high peak power?106 W?was developed,which based on the master oscillator power amplifier?MOPA?structure.Firstly,a SESAM mode-locked all solid-state Yb:KGW ultrashort pulse oscillator with high beam quality was developed.The average output power of the femtosecond or picosecond pulses outputted from the oscillator at 1037 nm is up to 2.2 W,the pulse repetition rate is about 43 MHz,the light-light conversion efficiency is 22%,and the pulse duration can increase from 395 fs to 1.6 ps by adjusting the amount of negative dispersion in the laser cavity.Afterwards,a pulse picker was used to reduce the repetition rate of the ultrashort pulses outputted from the oscillator to below 10 KHz.And then,the seed pulses were injected into a 6-pass Yb:KGW solidstate amplifier for amplification.The pulse energy of the ultrashort pulses outputted from the amplifier is about 2.8 m J,and the corresponding peak power is up to 4.9×106 W. |
PDF Full Text Request