Research On Application Of Emerging 2D Chalcogenides In Pulsed Fiber Laser

Pulsed fiber lasers have been widely concerned by researchers due to its advantages of compact structure,easy integration,high beam quality and high stability.At present,the technologies that can convert continuous-wave fiber laser into pulsed fiber laser mainly include Q-swtiching and mode-locking.Q-switching can generally obtain pulsed fiber lasers with pulse width of nanosecond or microsecond,which have high pulse energy and can be used in industrial field,including laser marking,laser cleaning and laser peening.Compared with Q-switching,mode-locking can obtain pulsed fiber lasers with pulse width of picosecond or femtosecond,which have ultra-narrow pulse width and high peak power and can be used in medical surgery,spectroscopy,ultra-precision machining and precision ranging.Passive Q-switching and mode-locking are important methods to obtain pulsed laser output.Among them,the saturable absorber(SA)is used as an optical modulator to obtain pulse laser output,which has been widely studied.Semiconductor saturable absorber mirror(SESAM)is the most mature SA for commercial application.The greatest advantage of SESAM is stability.However,SESAM also has many disadvantages,including complex preparation,high cost,narrow operating wavelength and low damage threshold.Therefore,the research on new SA materials has attracted extensive attention.With the fast development of research on SA,more and more materials have been found to have SA properties,including carbon nanotubes(CNTs),graphene,black phosphorus(BP),transition metal dichalcogenides(TMDs),topological insulators(TIs),Mxenes and so on.Among them,two-dimensional layered materials have been widely used as SA in pulsed fiber lasers due to their advantages of simple fabrication,low cost,broadband working range and fast optical response time.The pulsed laser based on 2D materials-based SA can obtain excellent output performance.However,these 2D materials also have some disadvantages,such as weak absorption and low modulation depth of graphene,instability of BP in air,relatively long exciton recovery time of TMDs,high production cost of TIs and so on.In order to obtain more comprehensive and stable SAs,it is of great significance for the research and development of new SA materials.The SA properties of several new 2D chalcogenides have been studied,including platinum diselenide(PtSe2),rhenium disulfide(ReS2),and tin disulfide(SnS2).The application of these materials in pulsed lasers has also been studied.The main research achievements list as follows:(1)A novel optical deposition method has been developed to successfully prepare a PtSe2-based SA.The SA can be applied to a 1?m fiber laser and obtain mode-locked pulse output.Currently reported optical deposition processes are generally carried out in the liquid environment,while this experiment is completed in the non-liquid environment.By using simple selenization,vertically standing PtSe2 film can be prepared on quartz substrate.The as-prepared PtSe2 grows uniformly and has good crystallinity.The thickness of the PtSe2 film is about 24 nm.A PtSe2/PMMA composite film can be prepared by using PMMA to transfer the PtSe2 film from quartz substrate.The composite film is put into the home-made optical deposition system.Through the optical gradient force,part of PtSe2 sheets comes out from the composite film and deposit on the fiber end face which forms the PtSe2-based SA.The SA is applied directly in Yb-doped fiber laser and obtain mode-locked pulse output.The central wavelength,pulse width and repetition of the mode-locked laser are 1067.5 nm,1.9 ns and 4.45MHz,respectively.(2)A ReS2-based SA can be prepared by some low-cost methods.The ReS2-based SA is used in an Er-doped fiber laser and obtain Q-switching or mode-locking pulse output,respectively.By using simple chemical synthesis method,sulfur powder and rhenium powder can be synthesized into ReS2 powder.By XRD and Raman characterization,it can be found that the ReS2 sample has layered structure and good crystallinity.By means of liquid phase exfoliation(LPE),ReS2 powder can be prepared in to ReS2 nanosheets solution.The size of the nanosheets are below 200 nm and the thickness is about 3-4 nm.Mixing the nanosheets solution with 4wt%PVA solution,a ReS2-based SA can be obtained.By changing the preparation parameters of the SA and the length of the laser cavity,Q-switched and mode-locked pulse output can be obtained in the Er-doped fiber laser,repectively.Among them,the pulse repetition of the obtained Q-switched pulse output can vary from 56.8 kHz to 73.5 kHz,while the pulse width can vary from 9.74 ?s to 2.4?s,and the maximum pulse energy is 18.88 nJ.The obtained mode-locked pulse has high stability,with pulse repetition of 7.2 MHz,maximum output power of 6.12 mW and maximum pulse energy of 0.85 nJ.(3)The nonlinear optical response of SnS2 nanosheets film has been investigated by femtosecond pulesed laser fo the first time.By using simple sulfuration,vertically grown SnS2 nanosheets film can be prepared.The as-prepared SnS2 nanosheets have layered structure and good crystallinity.The thickness of single nanosheet is about 18.4 nm.The nonlinear response of SnS2 nanosheets film is tested by using a Z-scan platform equipped with femtosecond pulsed laser.The result shows that the SnS2 nanosheets film has excellent saturable absorption property.The modulation depth and saturable absorption intensity are measured to be 11.7%and 1.9 mW/cm2,respectively.The nonlinear coefficient p is measured to be-(1.24±0.12)×103 cm/MW.The as-prepared SnS2 film has potential application in the field of femtosecond pulesed laser.