| Nowdays, femtosecond laser have been a powerful tool for human to know and transform the whole world. Due to ultrashort laser pulse possess ultrashort duration and superhigh peak power, it is widely applied to physics, chemistry, biology and other fields. Yb3+ion doped crystal is condidered to be the very best candidate for achieving femtosecond lasers at 1 μm wavelength region. Recently, a strong research efforts is dedicated towards the ultimate goal to generate both high average power and sub-100 fs pulses from the oscillator. The key challenge is to achieve sufficiently broad gain bandwidth in the laser oscillator with good power scaling capabilities. Therefore, it is meaningful to explore novel laser gain crystal for achieving the goal.In this paper, the spectroscopy and ultrafast laser characteristics of new disordered Yb:GAGG, Yb:LuGGG, Yb:CTGG garnet crystals and Yb:SYB borate crystal are systemically studied. In chapter 2, the principles of pulse self-start, shaping and stabilization mechanism in the mode-locked solid-state laser have been analyzed. The function between the pulse duration and laser parameters are theoretically given.In chapter 3, the spectroscopy and ultrafast laser characteristics of Yb:GAGG crystal are investigated. Due to the random replacement of Al3+ ions in the lattice, the emission spetra are inhomogeneously broadened. With a semiconductor saturable absorber mirror for passive mode locking, pulses as short as 422 fs at central wavelength of 1029 nm are obtained. The maximum average power is 1.1 W, corresponding to a slope efficiency of 20%. A diode-pumped Yb:GAGG mode-locked bulk laser based on chemically reduced graphene oxide (RGO) has been demonstrated. Pulses with duration of 643 fs were produced at the central wavelength of 1041.1 nm. A maximum average output power of 0.8 W is obtained from the RGO mode-locked laser, corresponding to a slope efficiency of 20.1% and a pulse energy of 17.8 nJ. The results indicate that RGO is suitbale for obtaining high-power and high-efficiecny ultrafat lasers. Moreover, few-layered graphene oxide (GO) have been successfully fabricated and applied to realize femtosecond mode locked bulk laser. Pulses as short as 493 fs are achieved with dispersion compensation, and a maximum average output power of 500 mW is obtained, corresponding to a pulse energy of 10.9 nJ. The results reveal that although the functional groups may bring unexpected effects on high-efficiency mode-locked operation, the water-soluble property is much helpful fro obtaining large-size uniform-quality atom-thin GO sheets (better controllability) and make the SAM fabucating process easier with better repeatability.The spectroscopic properties and ultrafast lasing characteristics of Yb:LuGGG crystal have been also investigated in chapter 3. The absorption cross section shows a widened form in the 940 nm wavelength region, which attributed to the random distribution of Lu3+ and Gd3+ ions at the dodecahedral lattice sites in the Yb:LuGGG crystal. The FWHM of the emission band around 1025 nm amounts to 14.7 nm, which is larger than that of Yb:GGG (12 nm) and Yb:GAGG (13.8 nm). Under passive mode-locking operation, the laser emits near transform-limited pulses at 1029.6 nm or 1026.8 nm. For 1030-nm band operation, the maximum output power can reach 1.3 W, with the pulse duration of 324 fs, the peak power of 69.2 kW and the corresponding slope efficiency of 41.6%. By optimizing the cavity design, pulses as short as 188 fs have been achieved with the slope efficiency of 27.1%. The results illustrate that Yb:LuGGG is an excellent gain medium for achieving high-efficiency and high-peak-power ultrafast solid-state laser.In chapter 4, the spectroscopic properties and ultrafast lasing characteristics of high disordered Yb.CTGG crystal have been studied. The FWHM of the emission band can reach up to 30 nm. With dispersion compensation,389 fs pulses at the central wavelength 1037.8 nm are obtained with an output power of 420 mW. Besides, two novel solid solutions of Yb:YAG and Ca3Al2(SiO4)3, Yb:YAG and Mg3Al2(SiO4)3 in various molar ratios are synthesized by solid-state reactions, respectively. The spectral bandwidth remarkably increase with increasing M3Al2(SiO4)3 (M=Ca, Mg) contents, and the maximal full width at half maximum (FWHM) of absorption and emission spectra for the solid solutions are almost 3 and 1 times larger than that of Yb:YAG, respectively. This large broadening of spectral bandwidth can be attributed to the inhomogeneity in the local environment of Yb3+ caused by the cationic substitutions of Ca2+ (Mg2+) for Y3+, Si4+ for Al3+ and the high crystal-field strengths caused by distorted host sites. This demonstration brings a new conception to obtain disordered crystal,In chapter 5, the spectroscopic properties and ultrafast laser performance of Yb:Sr3Y2(BO3)4 (SYB) crystal have been demonstrated.116 fs,120 fs and 126 fs pulses lasers are generated with more than 1 W average output power from the a-cut, b-cut and c-cut Yb.SYB based oscillators, respectively. The corresponding slope efficiency and optical to optical efficiency can reach to 49-54% and 31-33%, respectively. Besudes, the Yb:SYB laser is driven to work in SESAM-assisted Kerr-lens mode-locking (KLM) operation, and 58 fs pulses are generated at the central wavelength of 1054.6 nm. A maximum average output power reach 400 mW with a slope efficiency of 13.5%. The experimental results indicate Yb:SYB crystal as a promising candidate for achieving ultrashort lasers. |
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