Diode-Pumped Ytterbium-Doped Femtosecond Laser And Synchronously Pumped Femtosecond Optical Parametric Oscillator

Ultra-short pulses at near-mid-infrared wavelength（NIR-MIR）are of great importance in fields such as laser micro matching,two photon polymerization,THz generation,coherent anti-Stokes Raman scattering（CARS）,optical communication,infrared imaging guidance detectors,and others.At present,there are two methods to obtain the NIR-MIR laser source.One is stimulated radiation amplification based on laser gain medium,the other is nonlinear frequency conversion.In the last twenty years,with the rapid development and maturity of laser diode（LD）technology and the appearance of various new ytterbium doped crystals,high power all-solid-state femtosecond lasers at 1μm have developed rapidly.However,because of the limited energy level structure of the gain medium,it is difficult to generate ultrashort pulses longer than 3μm based on the stimulated radiation amplification method.As a mature nonlinear frequency conversion technology,optical parametric oscillator（OPO）has the advantages of broadband tunability,good coherence,high signal-to-noise ratio and good beam quality,which can extend the laser from 1μm to MIR wavelength.In this thesis,we research the diode-pumped ytterbium-doped mode-locked laser oscillator and high power,widely tunable femtosecond OPO at NIR-MIR wavelength synchronously pumped by 1μm laser.The main research contents and innovative achievements of this thesis are as follows:1.In order to generate ultra-short laser pulses with high power and short pulse width from ytterbium-doped femtosecond laser oscillator,the output characteristics of a976 nm LD pumped femtosecond Yb:CALGO laser are researched by designing and optimizing the resonator based on ABCD matrix theory and using SESAM mode-locked mode.The laser beam quality（M²<1.02）is close to the diffraction limit at the maximum average output power of 10 W.At the repetition rate of 71.66MHz,the mode-locked pulses with pulse durations of 247 fs,single pulse energy of140 n J and central wavelength of 1041 nm are obtained.2.High-power LD directly pumped SESAM mode-locked femtosecond Yb:KGW laser is demonstrated.The maximum average power of the output laser is as high as 13 W,which is the highest power obtained from the SESAM mode-locked single-bulk Ytterbium-doped femtosecond laser oscillator.The negative dispersion of 5800fs² is compensated by chirped mirror in the cavity,the measured pulse duration of mode-locked pulse is 261 fs,which is close to the limit of 222 fs.Next,an engineering prototype of the femtosecond Yb:KGW laser was developed,with an average output laser power of 10.15 W,a pulse width of 325 fs and a central wavelength of 1048 nm.3.A novel experimental scheme about green laser pumped idler-resonant femtosecond Bi B₃O₆ OPO is proposed,which further scales the output power and optimizes the beam quality for the idler.The idler can be continuously tuned in the wavelength ranges of 1100-1540 nm.The maximum output power is 400 m W,corresponding to a pulse duration of 80 fs at 1305 nm.The beam quality is 1.8 at 1150 nm.Next,the dual wavelength phenomenon of the idler is found based on Bi BO crystal,which can be tuned from 1394 nm and 1469 nm to 1405 nm and 1456 nm,with a maximum power of 200 mW.4.We research on the output characteristics of femtosecond Mg O:PPLN OPO tunable across NIR-MIR wavelength pumped synchronously by high power all-solid-state Yb:KGW laser.The signal pulses with a maximum output power of 2.2 W are obtained at 1500 nm.The range of signal and idler wavelengths is 1377-1730 nm and 2539-4191 nm,respectively.The signal has the shortest pulse width of 170 fs at 1428 nm.The full Width at Half Maximum（FWHM）is 185 nm at 3613 nm.Next,using the Ytterbium-doped fiber amplifier as pumping source of OPO,5.4 W of the signal and 2.5 W of the idler are obtained at 1546 nm and 3086 nm,respectively, corresponding to the overall optical-optical conversion efficiency of 49.4%,which is the highest power obtained from femtosecond Mg O:PPLN OPO at present.The power stability RMS of the signal and the idler in 1.5 hours is 0.53%and 1.2%, respectively.The signal has the shortest pulse duration of 784 fs at 1546 nm.