| High-power visible lasers with good beam quality have a variety of applications in the field of industry,medicine and entertainment.Among them,pulse lasers such as Q-switching gaint pulses and ultrafast pulses with femtosecond pulse width attract more and more attention in recent years.In this dissertation,power scaled laser operations to Watt-level in green,orange,red,and deep red visible spectral range were achieved by diode-single-end pumping Pr3+-doped LiYF4 crystal with the help of thermal management system designed by ourself.The pump source was a multi-mode GaN LD integrated by Polarization Beam Combining technique.The average output power in each of the visible spectral range all reached Watt-level.The maxmimum output power was 2.3 W for 640 nm emission.For all these visible lasers,beam propagation factors M2 were less than 1.8,indicatinggood laser beam qualities.Initial lasing at 604 nm without the aid of etalon was demenstrated and the gain-swiching mechanism was investigated,for the first time as far as we know.The output power characteristics were stimulated by solving rate equations of their energy level systems.Furturmore,absorption and emission spectral characteristics of c-cut Pr3:LiYF4 were investigated and Judd-Oflet(J-O)theory was included.Dual-wavelength laser emission at 696(3P0?3F3)and 719 nm(3P0?3F4)pumped by GaN-LD was demonstrated by using a c-cut Pr3:Li YF4,for the first time to our knowledge.The output powers of the two wavelengths were also stimulated by employing rate equations.Providing that the CW laser operatins were investigated fully,high performance Q-switching lasers in the visible spectral range were achieved by using TI Bi2Se3,and QDs CdTe/CdS saturable absorbers.For TI Bi2Se3,Q-switching wavelengths were 721,640 and 607 nm,the corresponding narrowest pulse widths,maximum pulse energies and pulse peak powers were(263 ns,0.19[J,0.71 W),(210 ns,0.15 ?J,0.73 W)and(368 ns,0.17 ?J,0.46 W),respectively.On the other hand,for QDs CdTe/CdS,Q-switching wavelengths were 721,640,607 and 522 nm,the corresponding narrowest pulse widths,maximum pulse energies and pulse peak powers were(195 ns,0.17 ?J,0.87 W),(295 ns,0.19 ?J,0.63 W),(226 ns,0.32 ?J,1.4 W)and(235 ns,0.21 ?J,0.9 W),respectively,which were the best performance among all the Q-switching visible lasers using nano-sheet materials as saturable absorbers.The theory of nano-sheet material passive Q-switching at 640 nm based on Pr:YLF was then investigated by solving rate equations.The influences of megascopic properties for nano-sheet saturable absorbers such as initial transmittance,modulation depth,saturable energy and even thickness on the performance of Q-switching were also investigated.Providing that the CW laser operatins and Q-switching pulse operations were explored sufficiently,achieving mode-locking lasers with ultra-fast pulses would be our next goal.High power self-mode-locked visible lasers in the green and red spectral range based on Pr3+:YLF4 with repetition rates of tens and hundreds of MHz were demonstrated.By employing a double-end pumped scheme,more than 0.68 W and 1.44 W average output power operating in the self-mode-locked state for 522 and 640 nm were extracted with an absorbed pump power of-2.8 W,respectively,leading to slop efficiencies of 29.9%and 57.3%.The output pulse trains and power spectrums demonstrating steady mode-locked operations at the maximum output power can be sustained for hours.Mechanism for the self-mode-locking effect was also analyzed theoratically.The pulse widths of the Pr:YLF mode-locked lasers were constrained to be above thousands of femtosecond by the limited gain bandwidth.Thanks to the width gain band,it has the protential to generate femtosecond ultra-fast laser pulses for Pr:CaF2 crystal,while the fluorescence intensity is such low that no lasing operation was ever reported by the crystal.The spectroscopic properties of the Pr-doped and Pr,Gd co-doped CaF2 crystals were investigated in this dissertation.The photoluminescence intensity in the visible region is drastically enhanced by codoping Gd3+ ions in Pr:CaF2 crystal.Relative emission intensities of the different emission lines were greatly improved.Continuous-Wave(CW)laser oscillation of Pr,Gd:CaF2 crystal at?642 nm was realized at room temperature,for the first time to our knowledge.Furthermore,based on a double-end pumping geometry,a power scaled laser operation of room-temperature CW red laser at 642 nm in Pr3+:CaF2 crystal codoped with Gd3+ was demonstrated.A maximum output power of?70 mW was obtained.The positive effect on slop efficiencies of lasers for double-end pumping method was also analysised quantitatively.By optimizing the doping concentration proportion of Pr3+,Gd3+ ions and optical quality of the crystal,and by employing better pumping technics,thus increasing the output power to hundred-milliwatt-level or higher,it should be possible to realize femtosecond laser pulses in the visible spectral range,which has never been realized as far as we know. |
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