Investigation On Ytterbium-doped Fiber Lasers Based On β-PbO And MXene Quantum Dots Saturable Absorbers

The ultra-fast fiber lasers combine the advantages of high pulse peak power,large output energy,and high integration with other components.In recent years,they have become a research hotspot in the laser field and they are widely used in optical imaging,biomedical science,mechanical processing and so on.In 2004,graphene was first successfully exfoliated from bulk graphite,which opened the door to the study of twodimensional(2D)nanomaterials.Five years later,graphene was successfully embedded into fiber lasers to generate femtosecond ultra-short pulses.Subsequently,various novel two-dimensional nanomaterials have been successfully applied to fiber lasers to achieve ultra-short pulse output,including transition metal dichalcogenides(TMDs),topological insulators(TIs),black phosphorus(BP),antimonene,bismuthene,which have the advantages of broadband nonlinear optical response,small optical loss,and easy preparation,therefore they can be ultilized as excellent saturable absorbers(SAs)for ultra-short pulse generation.Recently,we discovered two novel BP-like 2D nanomaterials—beta-lead oxide(β-PbO)and transition metal carbides and carbonitrides(MXene).After functionally modifying,they have excellent characteristics,such as high stability,strong nonlinearity.They can be used as saturable absorbers to achieve low threshold mode-locking regime in fiber lasers for ultra-short pulses generation.This dissertation will take advantages of the saturable absorption properties of β-PbO and MXene to achieve mode-locked ultra-short pulse output in fiber lasers.The main research works are as follows:1.Passive mode-locking technique in fiber lasers and the basic principles of saturable absorber are reviewed,and the measurement method of nonlinear optical characteristics—Z-scan technique is demonstrated in detail.2.The preparation process and characterization of β-PbO quantum dots(QDs)andβ-PbO QD / Polystyrene(PS)composite films are introduced in detail.The openaperture Z-scan technique was used to characterize their broadband nonlinear optical properties.Based on β-PbO QD / PS composite films saturable absorber,stable modelocked ultra-short pulse generation was achieved in an yetterbium-doped fiber laser(YDFL),and picosecond-level stable mode-locked pulses were achieved.The modelocking performance of this saturable absorber under water immersion was investigated.3.Electrochemical exfoliation and simultaneous fluorination method was employed to synthsize MXene quantum dots.The preparation process and characterization were introduced in detail.The open-aperture Z-scan technique was adopted to measure their broadband nonlinear optical characteristics.A saturable absorber device based on fluorinated MXene QDs was prepared by the photodeposition method.The picosecond-level stable mode-locked pulse output was realized in a YDFL,and the tunable spectral characteristics were observed.