Research On High Power All-fiber 1 Micron Ultrafast Laser Generation And Chirped Pulse Amplification Techniques

Ultrafast fiber lasers possess many attractive properties including simple design,high average and peak power output,environmentally stable and high electro-optical conversion efficiency.Therefore,they can be widely used in many fields such as highprecision micromachining,laser sensing,waveguide writing,and attosecond science.In the past decades,passively mode-locked technique has made a rapid development,which is one of the most important foundations to obtain ultrafast pulse output.In recent years,more attentions have been directed to fiber chirped pulse amplification(FCPA)system,just for the purposes of obtaining high peak power output and to maintain the advantages of fiber laser and fiber amplifier at the same time.Usually,this system consists of an all-fiber laser source and a free space pulse compressor.Recently,the developments of the dispersive wave source and the monolithic chirped-volume Bragg grating(CVBG)compressor provide a possibility for a new FCPA system with compact design.In this dissertation,we are dedicated to the ultrafast FCPA system with high average power,high peak power,and high integration.The main innovative achievements of this dissertation are presented as follows:1.Theoretical and experimental study on the all-fiber passively mode-locked laser generationBased on Schrodinger's nonlinear equation,the transmission dynamics of ultrafast pulse,and the linear and nonlinear effects of the optical fiber are carefully deduced and analyzed.Thereafter,kinds of passively mode-locked technologies are chosen to setup all-fiber laser oscillators,including all normal dispersion nonlinear polarization rotation(NPR)mode-locked with ring cavity,semiconductor saturable-absorber mirror(SESAM)mode-locked with linear cavity,SESAM mode-locked with ring cavity,and dispersion-managed mode-locked with ring cavity.These technologies can generate laser output with pulse width ranged from 1 to 100 ps within a wavelength ranged from 1030 to 1070 nm.2.The theoretical and experimental study of all-fiber picosecond pulse amplifiersBefore the experimental study of the 1 ?m Yb-doped fiber amplifier,the principles of fiber amplifier were theoretically analyzed from the energy level structure,from the absorption and emission section,and from the gain and bandwidth of the Yb-doped fiber.Moreover,in order to improve the amplification efficiency and reduce the signal reabsorption effect,laser amplification process is numerically simulated according to the rate equations.In the experimental study,high power and high energy ultrafast Ybdoped fiber amplifier were set up respectively,with the picosecond mode-locked laser as the seed sources.In 1030 nm region,by use of the three staged cladding pumped fiber amplifiers,an average output power of 101 W can be achieved with the pulse width of 36.6 ps.In 1064 nm region,with the laser frequency and pulse peak power of fiber amplifier being controlled by use of a long fiber stretcher and acoustic optical modulator(AOM)pulse selector,an average output power of 131 W with center wavelength of 1064 nm is achieved,and the measured pulse duration is 800 ps,corresponding to the pulse energy of 72 ?J.3.The study of high average power picosecond fiber chirp pulse amplification systemIn the theoretical study of the 1 ?m Yb-doped fiber chirp pulse amplification,the principle of diffraction grating pair pulse compressor was analyzed first.Thereafter,the suitable length of fiber stretcher,the trends of pulse width and spectral width under different incident powers are carefully studied through Fiberdesk numerical simulation software.In the experimental study,high power picosecond Yb-doped fiber CPA system is set up,which consists of a SESAM mode-locked seed source,a long fiber stretcher,three stages of cladding pumped fiber amplifiers and a transmission grating pair pulse compressor.Finally,a 106 W of average output power is obtained with center wavelength of 1064 nm,repetition rate of 4.93 MHz and the measured pulse duration is 13.6 ps with peak power of 1.6 MW.After precise design,the picosecond fiber CPA system has been optically-mechanically-electrically integrated.4.The study of high peak power and high average power femtosecond fiber chirp pulse amplification systemBy means of nonlinear frequency conversion technology,a wide-spectrum dispersive wave source is developed and used to build a femtosecond CPA system.In developing the 1 ?m dispersive wave source,we set up an Er-doped mode-locked fiber laser and the frequency is shifted to 1 ?m through a short segment of highly nonlinear fiber(HNLF).The generation process of dispersion wave is simulated ahead of time with the help of Matlab software.After that,we set up a high peak power femtosecond fiber CPA system,which consists of above-mentioned dispersive wave source,a long fiber stretcher,an AOM pulse selector and a grating pair compressor.As a result,an average output power of 7.7 W with center wavelength of 1065.1 nm is achieved and the repetition rate is 1.09 MHz with the pulse duration of 270 fs,corresponding to the peak power of 26 MW.Finally,in order to further improve the average output power and system integration,a CVBG pulse compressor instead of grating pair compressor is used to set up high average power femtosecond chirp pulse amplification system with compact structure.It turns out that the 1064 nm laser system can output an average power of 107 W with repetition rate of 17.5 MHz and pulse duration of 566 fs.