Investigation On Amplification Of Novel Near-infrared Fiber Pulse Lasers And The Generation Of Vector Beams

Pulsed fiber lasers have very broad application prospects in the fields of biomedicine,precision processing,and laser sensing due to their superior characteristics,such as small structure,good heat dissipation,good beam quality,and high light-to-light conversion efficiency.Passive Q-switching technology based on saturable absorbers has been developed rapidly in the past few decades.With increasing demands for high power and high energy ultra-short pulse lasers,femtosecond pulse amplification systems based on fiber chirped pulse amplification technology have gradually attracted wide attentions from researchers.In recent years,the spatial light field controlling of lasers has also become an important development direction in the laser field.The cylindrical vector beam has potential application values in optical trapping and manipulation,ultra-high resolution imaging,etc,owing to its unique light field distribution and focusing characteristics.Therefore,this thesis mainly focuses on the experiments of passive Q-switched pulse generation and laser amplification in fiber lasers and the simulation design of optical components that generate cylindrical vector light.The main research contents of this paper are as follows:1.Based on an organic nonlinear optical material,maleic acid-doped polyaniline saturable absorber,a stable Q-switched pulse operation was realized in an erbium-doped ring fiber laser for the first time.The twin detector technique was used to characterize the saturable absorption characteristics of the saturable absorber.The measured results indicate a modulation depth of 13% and saturation intensity of 0.336 MW/cm2.The center wavelength of the output Q-switched pulse is around 1560 nm,and the spectral width is 5 nm.When the pump power increases from 160 m W to 440 m W,the repetition rate changes from 33.78 k Hz to 87.01 k Hz,and the narrowest pulse width is 2.29 μs.The maximum output power is 3.4 m W,corresponding to a single pulse energy of 54.64 n J.2.Based on the chirped pulse amplification technology,a Ytterbium-doped fiber pulse amplification system was independently designed and built.In this experiment,a commercial SESAM mode-locked femtosecond fiber oscillator was used as the seed source,and the ordinary single-mode polarization-maintaining fiber and transmission grating pair were used as stretcher and compressor,respectively.The all polarization-maintaining fiber structure of the system ensures the stability of output power and compactness of the Ytterbium-doped amplifier.Finally,an ultrashort pulse laser with a center wavelength of 1041 nm,a spectral width of 9 nm,a pulse width of 235 fs,and an average power of 3.2 W was realized,corresponding to a maximum single pulse energy of 71 n J.3.By simulating the focus characteristics of radial vector polarized light and seeking the vector solutions of Maxwell’s equations,a nano-sized optical element—a combination structure of concentric circular metal grating and spiral phase plate was designed.The normal incidence left-handed circularly polarized Gaussian beam with a wavelength of 1030 nm is used as the light source.After passing through the element,standard radial vector beam is theoretically realized.The specific parameters of the designed element are: grating and spiral phase plate made of metal aluminum and Si O2 respectively,where the grating has a period of 200 nm,a duty ratio of 1/2,and a groove depth of 300 nm.The spiral phase plate is divided into eight steps in a clockwise direction,with each step increasing by 300 nm.The final simulation result meets with the optical field distribution and polarization distribution characteristics of radial vector light.