【作者】 周慧；

【导师】 曾和平； 丁良恩；

【作者基本信息】 华东师范大学 ， 光学， 2014， 博士

【摘要】 紫外超短脉冲激光具有波长短、单光子能量高以及高时间分辨率等特性,在精细微纳加工、超快强场光学、光频标测量学、飞秒化学以及超快泵浦探测等方面具有相当广泛的应用前景。直接利用受激辐射获得紫外超短脉冲是相当困难的,因此利用非线性频率转换技术,将红外或可见光波段的超短脉冲转换到紫外波段是目前获得紫外超短脉冲最快捷有效的方式。本论文围绕紫外与真空紫外飞秒脉冲的产生及应用展开。首先以商售的钛宝石激光器为种子源,利用级联频率上转换技术,在不同的固体介质与气体介质中实现了深紫外、真空紫外以及极紫外波段的超短脉冲输出。主要包括：1.使用10Hz的钛宝石激光器为种子源,利用BBO晶体倍频-补偿-和频的方案,实现了1.6mJ的267nm紫外超短脉冲输出,紫外脉冲宽度为190fs,红外-紫外转换效率高达7%。2.采用紫外倍频晶体KBBF将钛宝石激光器的二倍频光直接进行频率上转换到200nm紫外波段,获得单脉冲能量高达0.1mJ的紫外超短脉冲,并且为了补偿在倍频过程中由晶体引入的脉冲展宽,利用一对熔融石英棱镜对其进行色散补偿,最终获得了780fs的超短紫外脉冲输出。3.使用钛宝石激光器的二倍频光与三倍频光作为驱动源,惰性气体作为非线性介质,利用其在强聚焦下的非线性效应,最终获得了单脉冲能量为6.4μJ的133nm真空紫外超短脉冲,单脉冲能量分别为251nJ,199nJ的89nm与79nm波段的极紫外超短脉冲。相比较于固体激光系统,光纤激光系统具有结构紧凑、泵浦阈值低、稳定性好等特点,是获得高功率高重复频率的紫外超短脉冲激光的稳定可靠的驱动源。本论文围绕紫外飞秒光纤激光系统进行了一系列的研究,以自行搭建的二极管泵浦的Yb:YAG陶瓷激光器为振荡源,采用主振荡功率放大与啁啾脉冲放大结合的方式,搭建了级联大模场光子晶体光纤放大系统,获得了重复频率为103MHz,输出功率为300W的1030nm红外激光,并利用BBO晶体对其进行四倍频获得了高功率258nm紫外超短脉冲激光输出。论文中针对紫外超短脉冲做了一系列初步应用。利用钛宝石激光器的三倍频267nm,研究了其在空气中的成丝效应,以及在双光丝干涉形成的等离子体光栅效应。除此之外,利用红外与紫外双色场下的荧光增强原理,研究了混合气体中的复合解离等现象。除此之外,论文中还探索了其他新型材料紫外脉冲驱动源,如具有宽调谐范围的Yb:YSO激光器,为可调谐紫外激光光源的实现提供了稳定可靠的基频光源。利用非线性偏振旋转锁模原理搭建了超短脉冲输出的掺铒光纤激光器与掺镱光纤激光器,为全光纤化的紫外超短脉冲激光系统的实现提供了驱动源。更多还原

【Abstract】 Ultraviolet (UV) ultrashort pulses, which combine the characters of short wavelengths, high photon energy as well as high time resolution, have a wide spread applications in many areas, such as precision nano-machining, strong field optics, optical frequency measurements, femtosecond chemistry and ultrafast pump and probe techniques. However, since it is difficult to obtain the UV ultrashort pulses directly through the stimulated radiation, the most efficient and effective way is frequency up-conversion, which is converting infrared and visible ultrashort pulses to UV wavelength.In this dissertation, the work focused on the UV and vacuum ultraviolet (VUV) generation as well as some primary application of the UV ultrashort applications. In the beginning of the work, the frequency up-conversion was based on a commercial Ti: sapphire laser, and the deep ultraviolet (DUV), VUV and extreme ultraviolet (XUV) ultrashort pulses were obtained using different solid state mediums and gas mediums:1. BBO crystals were used in a frequency doubling-compensation-tripling scheme, and with this method, the267nm UV pulses with the output power of1.6mJ, which had a repetition rate of10Hz and pulse duration of190fs were obtained, the corresponding conversion efficiency was7%.2. The ultrashort pulses at200nm were obtained in a frequency doubling process with a KBBF crystal, in which the injecting seed-pulse was the second harmonic of the10Hz Ti:sapphire laser. The DUV pulse energy achieved0.1mJ, and the system used a pair of prisms to compensate the dispersion introduced by the upconversion crystals, thus the duration of the200nm pulses was shortened to780fs.3. The second harmonic and third harmonic of a10Hz Ti:sapphire laser were focused onto an argon target under a gas jet in a vacuum cell to achieve relatively high beam intensity, and the133-nm VUV pulses,89-nm and79-nm XUV pulses were generated within the laser-argon interaction area, with the pulse energy of6.4μJ,251nJ, and199nJ, respectively.Compared to solid state laser systems, the fiber laser system with a compact structure, low pumping threshold, good stability as well as perfect beam quality, was the robust and reliable driving source for the high repetition and high power UV pulses generation. The power amplification was essential for the generation of UV pulses, since the up-conversion efficiency was relatively low. The dissertation demonstrated a master-oscillator amplifier system combing with the chirped pulse amplification and cascade amplification, and built a multi-stage photonic crystal fiber amplifier to achieve300W output pwer with seeding pulses from an Yb: YAG ceramic oscillator with a repetition rate of103MHz. Part of the infrared output was upcon verted to258nm with two BBO crystals. The maximum ultraviolet output reached1.6W.The dissertation also demonstrated some applications of the UV pulses. The filamentary propagation of the intense267nm ultrashort pulse was studied, as well as filamentary plasma gratings formed by the noncollinear interaction of synchronized filaments. Beyond that, collisions of nitrogen and argon gas mixture with energetic electrons accelerated by Bragg incident intense infrared femtosecond laser pulses in ultraviolet filamentary plasma gratings were also investigated.In addition, new ultraviolet pulse driving sources were explored in the dissertation, such as tunable Yb:YSO laser which had a wide tuning range of110nm, providing the possibility of the tunable ultraviolet laser. The erbium-doped fiber laser (EDFL) as well as the ytterbium-doped fiber laser (YDFL) were built with the nonlinear polarization rotation method, providing the driving source for the all fiber UV-pulse generation system.更多还原