| Ultrashort laser pulses have a series of advantages,such as high peak power,narrow width of pulse,and wide spectrum.It has quite important value of application in the field of micro-world exploration,material micro-processing,and bio-medicine.At present,considerable progress has been made in the study of mode-locked fiber lasers based on nonlinear fiber ring mirrors,nonlinear polarization rotation effects,semiconductor saturable absorption mirrors(SESAM),and nanomaterial saturable absorbers.In these applications,gold nanomaterials have a high nonlinear coefficient and ultrafast response time,as well as good fiber compatibility and ease of preparation,so that it is possible to achieve mode-locked laser pulse output,of course,by using the saturable absorption properties of gold nanoparticles.Therefore the saturated absorption properties of gold nanoparticles have been widely concerned and used in the field of mode locking technology for the fiber and solid-state lasers.In this thesis,gold nanoparticle saturable absorbers were used for passive mode locking of ytterbium-doped fiber lasers,and nanosecond pulsed laser output with low repetition rate was obtained.Related characteristics of the mode-locked laser pulses were measured and analyzed.The main research content is as follows:(1)The types of saturable absorbers and their basic properties of different nanomaterials are briefly introduced.Two methods of coupling materials and light fields are introduced.Finally,The status quo of development of gold nanomaterials and modelocked fiber lasers based on gold nanomateriral saturable absorbers are described.(2)Using the Haus equation,the process of formation of mode-locked ultrashort pulses in fiber laser cavity and its influencing factors are theoretically analyzed.Then,the typical optical properties and saturation absorption principle of gold nanoparticles are discussed.(3)Different spherical gold nano-solutions were prepared experimentally,and the spectral absorption characteristics of the pure spherical gold nanometer solution,spherical gold nanometer solution mixed with sodium hydroxymethyl cellulose and gold nanorod solution were characterized.The optical fiber connector-type saturable absorber was prepared by a drop coating method and an optically driven deposition method,and its saturated absorption characteristics were measured.(4)An annular cavity ytterbium-doped fiber laser based on a spherical gold nanoparticle saturable absorber was experimentally constructed.The mode-locked pulse characteristics of a fiber connector-based gold nanosaturable absorber for a fiber laser were experimentally studied.The basic characteristics of Q-mode locking and continuous mode-locking pulses are analyzed.The phenomena such as soliton rain and the generation mechanism and characteristics of multi-wavelength mode locking are discussed.(5)An ytterbium-doped fiber laser based on a gold nanorod saturable absorber was experimentally constructed,and a saturable absorber prepared by an optical drive deposition method using optical fiber connector and tapered optical fiber was studied respectively.The characteristics of mode-locked pulse are compared with their experimental results.In addition,the phenomena and characteristics of dissipative soliton resonance pulse appeared in the experiment were analyzed and discussed.The comparison analysis of experimental results of two kinds of gold nanoparticle modelocked fiber lasers was performed. |
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