Research On Magnetron-sputtering Saturable Absorber Mode Locked Fiber Lasers

Ultrafast pulsed lasers have been widely used in many fields,including medical imaging,space ranging,ophthalmology,terahertz spectrum,material micro-processing and precision measurement.Compared with the traditional solid-state lasers and gas lasers,passively mode-locked fiber lasers have unique advantages（such as simple structure,low cost,good beam quality,strong environmental adaptability,etc.）,drawing widely concerned by scholars.Saturable absorber plays a key part in passively mode-locked fiber laser.It has a very close influence on the formation,pulse width and stability of mode-locked pulses.Up to now,the research of saturable absorbers has experienced from traditional semiconductor saturable absorber mirrors（SESAM）to some recent new nanomaterials,such as carbon nanotubes,graphene,topological insulators,transition metal sulfides and so on.Ultrafast fiber lasers based on these new nanomaterials have become a focus of researches in optics field.However,most of these reported ultrafast fiber lasers are confined to the laboratory and they are not used practically so far.It is of great significance to promote the practical application of fiber lasers.In this paper,practical saturable absorbers（SAs）were prepared with magnetron sputtering deposition method.The SAs were successfully applied in erbium doped fiber laser and thulium doped fiber laser,the longtime sustained operation of the fiber lasers was also experimentally proved.The main work of this paper was as follows:1)The dispersion effect and non-linear effect in optical fiber medium were introduced,and their influences on optical pulses in time domain and frequency domain was analyzed.Based on Maxwell equations,the basic transmission equations in optical fibers of optical pulses was deduced.Then,the basic mode-locking principle of mode-locked fiber lasers was summarized.The peak power relationship of mode-locked lasers and continue wave lasers was analyzed.The mode locking principle and three important parameters of the saturable absorber were introduced.2)MoS₂,Bi₂Se₃ and MoS₂/Bi₂Se₃ heterojunction Saturable absorbers were prepared by magnetron sputtering deposition method.The as prepared MoS₂,Bi₂Se₃ and MoS₂/Bi₂Se₃heterojunction samples were characterized by Raman spectroscopy and scanning electron microscopy.Z-scan system was used to measure the nonlinearity properties of the SAs.Based on the SAs,stable femtosecond mode-locked pulses was achieved in erbium-doped fiber lasers,in which MoS₂/Bi₂Se₃ heterojunction Saturable absorber mode-locked fiber laser had the narrowest pulse width of 586 fs.Moreover,the MoS₂ mode-locked fiber laser was enhanced.And the pulse width,average output power,pulse energy and frequency were 256fs,67mW,2nJ and 34.7MHz,respectively.3)α-In₂Se₃ saturable absorber was prepared by magnetron sputtering deposition method.The thickness and surface morphology of the films were characterized by scanning electron microscopy（SEM）.Raman spectra and linear absorption spectra of the films were measured,which proved the films to be good lattice quality.The non-linear property of theα-In₂Se₃sample was measured by twin-arm measurement and Z-scan technique.The wide-band saturable absorption property at 1,1.5 and 2μm ofα-In₂Se₃ was proved.Based onα-In₂Se₃SA,stable mode-locked pulses with pulse width of 276fs and 1.02ps were achieved in erbium-doped fiber laser and thulium-doped fiber laser,respectively.