| Ultrafast pulse laser has wide applications in scientific research. It is simple to achieve nanosecond, picosecond and femtosecond ultralpulse through passively Q-switched, mode-locked technology by saturable absorber. But the common saturable absorber has several defects such as instable, narrow wavelength and complicate fabrication process. SWCNT (Single Wall Carbon Nanotubes) and graphene have become a wide wavelength modulation saturable absorber due to their unique nonlinear optics characteristics. This article demonstrates the fabrication of SWCNT and graphene that were used for saturable absorber of Q-switched and mode-locked laser by a couple of methods and functional operation technique. In order to obtain ultrafast pulse output. In theory,focus on saturable absorbing principle of SWCNT and graphene, passively Q-switched and mode-locked of laser, and dynamics process of active or passive Q-switched and mode-locked laser. Experimental research is in major of passively Q-switched and mode-locked by saturable absorber as SWCNT and graphene, operation rules of laser and relevant factors that affect output pulses. As well as, optimizing the preparation technology of saturable absorber and relevant parameters of laser. This project would be of great significant for the application of carbon nanometer materials and the development of ultrafast pulse laser. The special projects and innovations is as follows:1) Fabrication and characterization of graphemeAt present, the preparation of graphene in laboratory basis on the reduction of graphite oxide and chemical vapor deposition (CVD). The former method needs to immerse graphite powder into strong acid (mixture of concentrated sulfuric acid and concentrated nitric acid). Then graphite oxide was obtained through oxidation progress of low, middle and high trmperature respectively. Finally, the graphite oxide was dioxide in high temperature tube furnace to receive graphene. Another method for preparation of graphene is CVD. Acetylene was induced in experiment for providing carbon atoms. Copper foil was used for growth substrate and catalyst. Hydrogen and argon were income to act as carrier gas and auxiliary gas. Graphene membrane was acquired in the temperature domain between850centigrade and1000centigrade.2) The preparation and characterization of SWCNT/graphene saturable absorberConsidering the requires of different preparation methods and lasers, the two types of carbon nanometer materials can be manufactured into saturable absorption liquid, saturable absorption mirrors and saturable absorption membranes. SWCNT and graphene prepared by reduction-oxide method could be made into saturable absorption liquid or sarurable absorption mirror by spinning. The graphene prepared by CVD could be attached on the surface of mirror or manufactured to saturable absorption membrane. In addition, we also had the testing of raman spectrum, TEM and transmittance to the saturable absorber of graphene.3) SWCNT passively Q-switched Nd:YAG laserThe mechnism of passively Q-switched pulses by SWCNT was analysised. The output characteristics of Q-switched side-pumped Nd:YAG solid state laser by SWCNT was obtained; in experiment. Acquiring the minimum pulse width of630ns with single pulse energy of28.3μJ. At last, the factors on the designing of Q-switched laser was analysised.4) Graphene-based passively Q-switched laserIn the experiment, graphene was used in1μmNd:YAG solid state laser,2μm Tm-doped fiber laser and2μmTm:YAP laser due to its wide band passively Q-switched characteristic Finally,we confirmed the wide band characteristic of graphene and analysise d the output characteristics of different lasers.5) Er-doped passively mode-locked fiber laserThe Er-doped fiber laser passively mode-locking operation was realized by nonlinear polarization rotation and graphene respectively. Numerical modeling was made in theory to fluorescence and spectrum sideband and a scheme of restraining their appearance was put forward which will be benefit for enhancing pump efficiency, shortening mode-locked pulse and improving the stability of pulses in the following experiment projects.6) The design of solid state laser cavity based on graphene mode-locking.After considering astigmatism, heat effect of laser gain medium and dispersion compensation, we calculated the stable region of the whole cavity and spot size in different position by using ABCD matrix. As a result, suitable component parameters, length, the position of saturable absorber and a special cavity based on graphene mode-locking was easy to be decided.The innovation of this article:(1) The innovation of saturable absorberBy using two kinds of new type saturable absorber such as S WCNT and graphene, we invent two types of methods to prepare saturable absorbor that is simple and practicable, costless and easily to be appropriate for any wavelength. The SWCNT and graphene saturable absorbor we acquired by these methods could preserve complete chemical structure and uniform distribution.(2) The innovation of research contentsa) Variety types of saturable absorber based on SWCNT and graphene was prepared. Choosing saturable absorber mirrors in solid state laser could decrease insertion loss Adopting saturable absorber membrane in fiber laser ensured all fiber cavity which would be more convenient;b) SWCNT, graphene saturable absorber for laser passively Q-switched Q, locking, and according to the pump power, cavity, the cavity length and output mirror transmittance and absorption saturation of the preparation technology was used to optimize the parameters of its stability;c) using the SWCNT saturable absorber pulse width630ns1.06μm passively Q-switched Q; using graphene saturable absorber to realize broadband passive Q, respectively,249ns Q switched pulse at1μ mNd:YAG in solid state lasers;1.4μs and2μm Tm:YAP solid laser pulse in760ns passively; Q pulse of2μm thulium doped fiber laser, which is now known as the shortest based on2μm passively Q-switched Q pulse width of the graphene;d) using graphene saturable absorber in the1550nm erbium-doped fiber laser is realized in passively mode-locked PS, because there was no compensation for the cavity dispersion, so the pulse width is bigger, join the dispersion compensation fiber can compress the pulse; e) mechanism of SWCNT, graphene saturable absorber is analyzed theoretically, the passive Q, mode-locking experiment, and gives the design scheme of solid-state mode-locked resonator; the material preparation and laser research linking, according to Q, a mode-locked laser with a saturable absorber to prepare the corresponding materials demand.(3) combining theory with experimentAccording to the energy band structure of SWCNT/graphene, the Pauli blocking principle and relativistic quantum theory, analysis and exploration of the saturable absorption mechanism, the selection and preparation of raw materials more suitable as a saturable absorber; starting from the nonlinear Schrodinger equation and Haus equation, SWCNT, dynamic process of graphene can be saturated Q switched laser, mode-locked, on and saturated absorption preparation technology parameters were optimized and the parameters of the laser. |
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