Research On Fiber Femtosecond Laser Technology For Three-Photon Bioimaging

The high-power femtosecond fiber lasers are widely used in laser processing,detection LiDAR,biological imaging and other fields based on the perfect characteristics of high beam quality,compactness,robustness and low cost.The 1.3-1.7-μm femtosecond lasers operating at the second near-infrared(NIR-Ⅱ)region are the ideal laser sources for the multiphoton bioimaging technology.However,the pulse energies of the existing NIR-Ⅱ ultrafast lasers cannot fulfill the requirements of the newly developed high-speed multiphoton bio-imaging technology.The central wavelength of the emitted erbium-doped ultrafast fiber laser located in the spectral range from 1520 nm to 1560 nm,which can be used as an ideal laser source for generating the 1.3-1.7-μm ultrafast lasers.In this dissertation,a high-power 1.5-μm ultrafast fiber laser system was proposed based on the mode-locked fiber laser oscillator and the chirped pulse fiber amplification technology.On this basis,nonlinear frequency conversion was employed to achieve the 1.3-1.7-μm ultrafast laser output.The research content of this paper is divided into the following three parts:1.Research on the high stability mode-locking fiber oscillator.Firstly,the mode-locking pulses dynamic evolution process of the all-polarization-maintaining fiber oscillator based on the nonlinear amplification loop mirror(NALM)was simulated using MATLAB.Secondly,on the basis of theoretical simulation,the mode-locking fiber lasers based on the NALM and the nonlinear polarization evolution(NPE)were experimentally constructed by carefully designing the cavity type,gain and loss of the oscillator.Finally,the experimental comparison showed that the NALM mode-locking fiber oscillator has higher stability and was selected as the seed source for subsequent laser amplification system.2.Study on all-polarization-maintaining fiber laser amplification and compression system based on the chirped pulse amplification(CPA)technology.First of all,the rate equations of the erbium-ytterbium co-doped fiber amplifier(EYDFA)were established to study the evolution dynamics of amplified pulses.Next,the home-made,all-PM NALM fiber oscillator was used as the laser source.The CPA system was in collaboration with dispersion management,spectral management,nonlinear management,and large-mode-area double-cladding erbiumytterbium co-doped fiber amplification.Eventually,the 31.12-MHz,474-fs,13.2-W high power laser pulse output was achieved.3.Study on nonlinear frequency conversion process of high-power 1560-nm femtosecond laser.Firstly,based on the SPM effect of the nonlinear spectral broadening process,the broadened spectrum with a spectral range of 1290 nm to 1750 nm was obtained by employing the 1560-nm high-power laser source.After spectral filtering,the ultrafast laser outputs with 1294-nm central wavelength,224-fs pulse duration,15.69-mW average power and 1706-nm central wavelength,269-fs pulse duration,99-mW average power were generated,respectively.Next,the second harmonic generation of the 1560-nm femtosecond laser pulses was developed employing the PPLN crystal.By the frequency doubling technology,the high-power 780-nm femtosecond laser with 781.7-nm central wavelength and 5.69-nm spectral bandwidth was obtained,which could act as an ideal pump source for amplifying the 1300-nm and 1700-nm femtosecond pulse lasers.