The Saturable Absorption Properties Of Topological Insulators And Other Two Dimensional Materials

Due to the excellent properties in time domain and frequency domain,pulsed lasers have been widely employed in various fields such as industrial processes,optical communications,medical treatment,scientific research,etc.As the optical modulator,saturable absorber(SA)is one of the key elements in pulsed lasers.However,the application of common semiconductor saturable absorption mirror(SESAM)is limited due to the narrow absorption band,complicated preparation technology and high cost.In recent years,some two-dimensional materials such as graphene,topological insulators and transition metal dichalcogenides,have attracted much attention due to their novel properties such as the sample preparation,broad absorption waveband,etc.In this thesis,the research focuses on the saturable absorption properties of topological insulators,graphene,and its heterojunctions.Using Z-scan,I-scan and Pump-probe measurements,the saturation intensity,modulation depth and relaxation time have been measured.The saturable absorbers based on topological insulator,graphene and its heterojunction were prepared,and applied in all-solid-state pulsed lasers.The main research contents and significant achievements are as follows:In chapter 1,the developments of SAs especially the two-dimensional SAs such as graphene and topological insulators,are introduced in detail.Then the saturable absorption properties of differently novel two-dimensional SAs are summarized.And the applications of the SAs in short-pulse lasers and ultrafast lasers are also introduced.Chapter 2 introduces the characterization of the third-order nonlinear optical properties and ultrafast dynamics of two-dimensional saturable absorbers.The third-order nonlinear characterization is mainly completed through the construction of Z-scan system and I-scan system.The ultrafast dynamics is characterized by degenerate and non-degenerate pump-probe systems.In chapter 3,by using spin coating-coreduction approach(SCCA),we fabricate large-area and uniform Bi2Te3 SAs with tunable thickness and coverage.The saturable absorption properties of as-prepared SAs with different thickness are measured.The results show that with the increase of thickness,the saturat?ion fluence decreased while the modulation depth increased,and the mechanism is analyzed.Then using as-prepared Bi2Te3 SAs in all-solid-state lasers at 1.0 ?m,stable Q-switched pulse laser with tunable parameters are obtained.In thoery,based on the modulation instability(MI)property and rate equations,we simulate the oversaturation process of Bi2Te3 with ultralow saturation fluence and the theory agrees with the experimental results.Finally,by using the Bi2Se3 SA in mid-infrared solid-state laser,a toplogical insulator-based 3.0?m Q-swtched laer is realized for the first timeIn chapter 4,based on the ultralow saturation fluence,by using a compact resonant cavity with large mode volume on the SA,a solid-state high repetition rate mode-locked laser is achieved for the first time with the output power of 181 mW,pulse duration of 8 ps and repetition rate of 948 MHz.In addition,we prepare topological insulator(TI)SAs with molecular beam epitaxy(MBE)method.By using coupled-cavity resonant passive mode-locking(RPM)technique,the problems of large absorption loss and low optical damage threshold for the SA in cavity are solved and stable Q-switched mode-locking pulse laser is obtained.In chapter 5,by adjusting the coating structure of reflecting mirror to change the electric field intensity of graphene,we successfully adjust and control the saturation fluence,modulation depth and unsaturated losses of the grapheme SA mirror(GSAM)In experiment,we prepare two GSAMs with absorption rate of 2.78%and 9.2%and successfully use them as optical modulators to realize 1.3?m mode-locked lasers,respectively.The dependences of output power and pulse duration on absorption of-GSAM are analyzed.In addition,we fabricate grapheme/MoS2 heterojuction material by intercalation method.Using it in a Yb:CALGO laser,the ultrafast laser is achieved with the pulse duration of 92 fs.Up to now,this is the shortest pulses generated from a laser based on grapene/MoS2 as SA.