【作者】 石自彬；

【导师】 张怀金；

【作者基本信息】 山东大学 ， 材料学， 2009， 硕士

【摘要】 半导体泵浦的全固化超短脉冲激光器在受控核聚变、等离子体物理学、遥控技术、化学和物理动力学、生物学、高速摄像、光通讯、光谱学、全息学以及非线性光学等领域有重要应用。锁模技术是获得超短脉冲的一种有效手段,经过锁模调制,每个脉冲的宽度与振荡线宽成反比。因为振荡线宽受到激光器净增益线宽的限制,即工作物质的增益带宽决定锁模脉冲宽度。因此,增益线宽越宽,越可能得到窄的锁模脉冲。尽管稀土离子掺杂的玻璃,具有较宽的发射谱线,但是较小的热导率,给其在高功率及高重复频率激光系统中的应用带来了很多不便。而一般晶体材料由于晶格结构的有序性,使得荧光谱线较窄,难以得到窄脉宽的激光。在这两者之间,存在着一类被称为无序晶体的材料,该材料不仅具有较有序晶体宽的吸收与发射谱线,而且具有比玻璃好的热学性质。这类材料是适合产生高功率及高重复频率超短脉冲激光的优秀激光晶体。本论文着眼于无序晶体的特点,对典型的掺钕钙铌镓石榴石Nd:Ca₃（NbGa）_2-xGa₃O₁₂（Nd:CNGG）和掺钕钙锂铌镓石榴石Nd:Ca₃Li_xNb_1.5+xGa_3.5-xO₁₂（Nd:CLNGG）无序激光晶体进行了系统探索研究,主要工作包括:（一）晶体生长的研究1、介绍了Nd:CNGG和Nd:CLNGG晶体生长的设备及工艺,讨论了影响晶体质量的因素。2、采用提拉法成功生长出大尺寸、高质量的Nd:CNGG和Nd:CLNGG激光晶体,并对其生长过程进行了系统的研究。（二）Nd:CNGG和Nd:CLNGG晶体物理性质的研究1、首次对Nd:CLNGG晶体的热学性能进行了系统研究,发现其热导率高于玻璃,因而比玻璃更适合应用在高功率泵浦的激光器中。2、对Nd:CNGG与Nd:CLNGG晶体的光谱进行了研究,发现两者均具有宽达十几纳米的吸收及发射带,与Nd掺杂的玻璃相当,揭示了其产生飞秒超短脉冲的可能性。（三）Nd:CNGG和Nd:CLNGG晶体连续激光特性的研究1、首次实现了LD泵浦Nd:CNGG和Nd:CLNGG晶体1.33μm连续激光输出,分别获得了158 mW、141 mW的最大连续激光输出,斜效率分别为2.0%、2.9%。2、在1.06μm波段获得了大功率连续激光输出,最大输出功率分别为4.03 W、3.81W,相应斜效率分别高达31%、30.3%,均超过了已有报道。（四）Nd:CNGG和Nd:CLNGG晶体被动调Q激光特性的研究1、首次使用Cr⁴⁺:YAG作为被动调Q器件,对Nd:CNGG进行了被动调Q激光性能研究。获得了最窄脉冲宽度、最大脉冲能量及最高峰值功率分别为12.9 ns、173.16μJ、12.3 kW的脉冲输出。通过光谱分析,发现Nd:CNGG激光器以双波长运转。2、首次使用Cr⁴⁺:YAG作为被动调Q器件,对Nd:CLNGG晶体进行了被动调Q激光性能研究。实现了最窄脉宽、最大脉冲能量、最高峰值功率分别为12.3 ns、265.3μJ、20.8 kW的被动调Q运转。与Nd:CNGG激光器不同,输出光谱中只有一个波长。（五）Nd:CNGG和Nd:CLNGG晶体被动锁模激光特性的研究1、以SESAM为被动锁模元件,采用色散补偿技术,对Nd:CNGG晶体的被动锁模激光特性进行了研究。首次实现了双波长同步锁模运转,所得脉冲宽度为5ps,重复频率88 MHz,每个同步锁模脉冲由脉宽660 fs、重复频率0.63 THz的准周期拍频脉冲组成。2、以SESAM为被动锁模元件,采用色散补偿技术,对Nd:CLNGG被动锁模激光特性进行了探索,于1061 nm处实现了最大平均功率486 mW,斜效率26%的连续锁模运转,所得脉冲宽度为900 fs。更多还原

【Abstract】 Diode-pumped solid-state ultrashort pulse lasers have important applications in thefields of controlled nuclear fusion, plasma physics, remote sensing, chemical andphysical dynamics, biology, high speed imaging, optical communications, spectroscopy,holography, nonlinear optics etc. Mode-locking technology is an efficient way to obtainultrashort lasers. The pulse duration is inversely proportional to the oscillationbandwidth by the mode-locking modulation, which is determined by the net gainbandwidth. That is to say, the pulse duration was determined by the gain bandwidth oflaser media. If the laser media have broad gain bandwidth, the short pulses are expected.Although rare earth active ions in glasses possess broad fluorescence spectra, theapplication in high-power or high repetition rate systems is limited by their smallthermal conductivity. Just restricted by the ordered crystal lattice, their fluorescencelines are too narrow to generate ultrashort pulse. Between the two regimes, there is aclass of materials called disordered crystals which have broad absorption and emissionspectra like glasses and excellent thermal properties like single crystals. They are thepromising laser media for high-power and high repetition rate ultrashort laser.Nd:CNGG and Nd:CLNGG laser crystals investigated in this dissertation are twotypical disordered laser crystals. The main contents include:1. The equipment and technology of Nd:CNGG and Nd:CLNGG for growth are introduced. The factors influenced on the crystal quality are also discussed. Large dimension and high quality Nd:CNGG and Nd:CLNGG crystals were successfully grown by the Czochralski method.2. Thermal property of Nd:CLNGG was systematic measured for the first time to our knowledge. It has been found that its thermal conductivity was higher than glasses. The absorption and fluorescence spectra were also measured for both Nd:CNGG and Nd:CLNGG crystals, which showed broader than 10 nm lines. So it has promising application in the ultrashort pulse regime.3. With a laser-diode （LD） as the pump source, continuous-wave（CW） laser performance at 1.33μm of Nd:CNGG and Nd:CLNGG crystals was demonstrated for the first time to our knowledge. The respective maximum powers of 158 mW and 141 mW for Nd:CNGG and Nd:CLNGG lasers were obtained with corresponding optical conversion efficiencies of 1.3% and 1.5%, and slope efficiencies of 2.0% and 2.9%.4. High-power dual-wavelength laser output with disordered Nd:CNGG crystal was demonstrated. CW output power of 4.03 W was obtained with a slope efficiency of 31%. With Cr⁴⁺:YAG as saturable absorber, the shortest pulse width, largest pulse energy, and highest peak power were achieved to be 12.9 ns, 173.16μJ, and 12.3 kW in passively Q-switched operations.5. High-power efficient LD pumped Nd:CNGG laser was also demonstrated. A maximum of 3.81 W with a slope efficiency of 30.3% was obtained in the CW laser operation. The passively Q-switched laser has been obtained for the first time to our knowledge. The shortest pulse width, largest pulse energy and highest peak power were determined to be 12.3 ns, 265.3μJ and 20.8 kW with Cr⁴⁺:YAG crystal as saturable absorber.6. With SESAM as saturable absorber, dual-wavelength synchronously mode-locked Nd:CNGG laser was demonstrated with dispersion compensation. The fundamental mode locked pulse train has a repetition rate of 88 MHz and pulse duration of 5 ps, with an average output power of about 90 mW. Autocorrelation measurements show that each of the synchronously mode-locked pulses consists of a train of quasi-periodic beat pulses with a 660 fs pulse width and a 0.63 THz repetition rate.7. The passive mode-locked Nd:CLNGG laser was also demonstrated as same as Nd:CLNGG laser. 900 fs CW mode-locked pulses was generated at the center of 1061 nm wavelength with a maximum average output power of 486 mW and a slope efficiency of 26%.更多还原