Research On High Power Ultrafast Yb-doped Fiber Laser And Its Application

High power ultrafast fiber lasers not only have the the advantages of compact structure,high conversion efficiency,good stability and good beam quality of traditional fiber lasers,but have also the unique superiority of high power,ultra-short pulse width,high pulse energy and so on.Therefore,it has a great value in lots of application such as laser micro-processing,optical communication,national defense military and scientific research.The Ytterbium-doped fiber with many advantages such as high conversion efficiency,high quantum efficiency,simple energy structure,wide gain bandwidth and long fluorescence lifetime is an excellent gain medium for high power fiber laser.Consequently,high power ytterbium-doped ultrafast fiber lasers have become a hot research topic in the field of fiber lasers in recent years.Aiming at the application of high-power ultra-fast lasers in laser micro-processing and other fields.this paper explores the practical miniaturized high-power ultra-fast fiber laser system,and makes effort on the resear-ch on the 1 μm high power ultrafast Yb-doped fiber laser and its application.The major research contents are as follows:Ⅰ.The semiconductor saturable absorber mirror(SESAM)is used as mode-locked device and the one reflector of laser cavity,Yb-doped fiber as the gain medium,and the 1064 nm chirped fiber grating as the other reflector in the cavity to construct a linear cavity mode-locked fiber laser.On the basis of realizing the stable output of mode-locked picosecond pulse laser,the master oscillator power-amplifier(MOPA)technology is used to build the optical power amplification system.Finally,we get the laser with the wavelength of 1065.4 nm,the 3 dB Spectral linewidth of 0.3 nm,the pulse width of 93 ps and the pulse repetition frequency of 5.15 MHz.The average output power of the laser is 21.45 W,and it can be obtained by calculation that the pulse has the energy of 4.16 uJ with the peak power of more than 44 kW.Ⅱ.Using the high power Yb-doped ultrafast fiber as the pump source,a piece of 300 m long phosphotus-doped silica fiber as the Raman gain medium and its random distributed backward Rayleigh scattering effect playing a part as the cavity mirror with the 1239 nm fiber grating,we have obtained the 1239 nm random Raman ultrashort pulse fiber lase.Pulse-pumped random Raman laser can automatically synchronize the pump pulse period with the laser round-trip time and obtain stable pulsed laser output.When the pump power is～0.98 W,the output power of the random laser is 6.1 mW.The random fiber laser has the central wavelength of 1239 nnm with the 3 dB spectral linewidth of 1.1 nm.and the pulse repetition frequency is 30.45 MHz.In addition,the output pulse is the noise-like pulse(NLP)with the pedestal width of more than 100 ps and the sharp peak pulse width of 1.5 ps.The signal-to-noise ratio of the fundamental radio frequency reaches more than 60 dB,and the output radio frequency has no obvious modulation,which indicates the stable operation of the random pulse laserⅢ.Taking passively mode-locked Yb-doped all-fiber lasers based on SESAM as the research object,the effect of intracavity filter bandwidth on the generation bound-state solitons in normal dispersion regime is experimentally studied.A heavily Yb-doped fiber as gain medium and a semiconductor saturable absorber mirror as the mode-locking element are used to obtain the 1064 nm all-fiber linear cavity mode-locked laser.Different picosecond mode-locked pulse states are observed when the different bandwidth(0.2 nm,1 nm,1.2 nm or 2.3 nm)of intracavity bandpass filter is selected.YWhen the filtering bandwidth is narrow(0.2 nm)or broad(2.3 nm),only stable dissipative solitons are obtained.In contrast,when the filtering bandwidth is moderate(l.Onm or 1.2 nm),we respectively observed the typical兀and-7π/2 bound-state dissipative solitons both with the pulse width of～3 ps and pulse interval of～14 ps.Then the bound-state soliton laser is amplified to～1.4 W by the master oscillator power amplification technique and inj ected into a photonic crystal fiber,generating the supercontinuum spectrum with the 10 dB spectrum of 750-1600 nm and the output power of 0.7 W,whose spectral flatness is better than that pumped by the traditional dissipative soliton.