【作者】 郭忠义；

【导师】 刘树田； 曲士良；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2008， 博士

【摘要】 随着激光技术的发展,近些年飞秒激光技术作为一种新兴的技术也越来越完善。因为飞秒激光脉冲通过多光子吸收机制能够得到免损伤、高质量的结果,飞秒激光正在逐渐成为一种在各种材料中显微加工光功能结构的强有力工具,到目前为止,通过飞秒激光直扫技术及全息加工技术,已经有很多高质量的光功能器件被加工出来,比如光波导、微光栅、光子晶体、以及一些光学衍射元件等。在本论文中,我们提出了几种加工光功能微结构的方法。同时,也给出了有关飞秒激光脉冲与材料相互作用过程的全面物理解释。具体的细节工作被总结如下所示:丰富了激光与透明玻璃相互作用的理论。使用同源脉冲在材料表面相干的技术,我们在材料表面得到了不同的微结构。使用同源双脉冲相干,不但在硅酸盐玻璃表面得到周期符合理论计算公式d =λ/[2sin(θ/2)]的常规微光栅,还得到了一种周期是常规光栅一半的非常规光栅。这种非常规光栅的深度也基本上达到常规光栅的一半。这种非常规光栅形成在常规光栅的每一个凸起槽上,我们认为非常规光栅形成是由于飞秒激光在介质中产生了非线性效应,产生了二次谐波所造成的。我们还研究了同源三脉冲在硅酸盐玻璃表面相干方面的实验,得到了二维六边形分布的周期性微结构,我们使用原子力显微镜(AFM)对这种结构进行了分析,结果显示微结构的周期与推导公式计算的结果符合得很好。使用400nm的激光直射到这个微结构上,得到的衍射结果显示出这种结构可以作为光束分束器,并且,一级衍射效率达到16.42%。当激光脉冲能量改变时,所形成的微结构的形貌也发生了改变。当脉冲能量比较高的时候,二维周期性微孔将会形成在玻璃样品的表面,然而,当脉冲能量比较低时,二维周期性中空薄圆台结构将会形成在样品表面。我们建立了一套理论模型来解释这种实验结果,这种所形成的微结构形貌随激光脉冲能量的变化是由于光压对等离子体的作用机制及激光熔融材料的马朗戈尼效应机制的共同作用的结果。提出一种实现光学涡旋的新方法,并实现光子轨道角动量叠加。提出了一种通过利用飞秒激光在硅酸盐玻璃中直写计算全息图的全新的方法,实现光学涡旋。这种通过飞秒激光诱导玻璃体内产生微爆的方法,不需要任何的材料预、后处理能够把光涡旋的计算全息图直写入透明玻璃体内。使用一束准直的He-Ne激光斜入射到所加工的计算全息图上,再现出了包括透射与反射衍射模式的光涡旋,总的衍射效率也达到了4.79%。提出一种利用飞秒激光脉冲在硅酸盐玻璃中加工组合计算全息图的新方法去实现光子轨道角动量的叠加。首先,我们先得到两个涡旋的计算全息图,再把他们按照设定的方式组合起来得到组合计算全息图。然后,利用飞秒激光脉冲把组合计算全息图直接写入到玻璃中。再使用一准直的He-Ne激光直射到组合计算全息图上,我们得到了携带不同拓扑荷的涡旋光束(包括一些新的拓扑荷)。对于新拓扑荷的产生,我们也给出了理论、实验解释。在金属膜上实现了计算全息光存储。从理论、实验上研究了飞秒激光与金属膜之间的相互作用。在飞秒脉冲与金膜相互作用的时候,金属膜上所形成的微结构形貌随着激光脉冲能量的变化而变化,当激光脉冲能量比较大的时候,能够得到金属膜上的烧蚀孔,然而,当激光脉冲的能量足够小的时候,我们在金属膜上得到了纳米锥结构。当飞秒脉冲与铝膜相互作用的时候,我们不仅在铝膜上得到烧蚀孔,而且还在玻璃基底上形成了纳米级的微孔,这也许又将提供一种纳米加工的全新途径。借助于计算全息的方法,我们使用飞秒脉冲把光信息存储在金属膜上。首先在计算机上对一物光波进行傅立叶变换,然后使用迂回相位编码方法,对所得到的复振幅分布进行编码。使用飞秒激光选择性烧蚀技术,把所得到的具有定向单元的CGH直写到沉积在玻璃基底上的金属膜上。最后,使用一束准直的He-Ne激光,物光波被很忠实的再现出来。飞秒脉冲直写在透明玻璃体内制备体光栅。高能量的飞秒激光脉冲与透明材料相互作用可以在材料内部形成多次微爆,并且能够在玻璃体内形成一条长的折射率改变痕迹。我们研究了不同能量激光脉冲、不同数量激光脉冲与玻璃相互作用所产生的微爆孔洞现象。当激光脉冲的能量达到20μJ的时候,激光脉冲在玻璃体内的作用痕迹长度基本上达到160μm,这为体光栅的加工提供了一种可能。我们研究了不同激光脉冲能量、不同激光扫描速度情况下所加工的光栅的衍射效率的变化,并在理论上解释了导致光栅衍射效率变化的物理机制。更多还原

【Abstract】 With the developments of the laser technology, femtosecond laser technologyis also becoming more and more consummate as a novel technology in recent years.Femtosecond laser pulse is a powerful tool for microfabrication and micro-machiningof various multi-functional structures in dielectric materials through multi-photon ab-sorption because of its high-quality and damage-free processing. Up to now, manyhigh-quality material processing techniques have been achieved by using femtosec-ond laser pulses with the methods of directly writing and holographic fabrication,such as waveguide, micro-gratings, photonic crystals and diffractive optical elements(DOE). In this dissertation, we propose several methods for fabrication of the photicfunctional microstructures. we also give a full and accurate theoretic interpretation forthe interactions between the femtosecond laser pulses and the materials. The researchwork has been summarized in detail as follows.improve the theory of the interaction between the laser and the transparentglass. Different periodic structures are attained on the surface of the transparent glassby a single shot of two or three pulses. When a single shot of two pulses interferedwith each other, not only did we get the ordinary grating whose periods accordedwith the theoretic equation d =λ/[2sin(θ/2)], but also obtained the extraordinarygrating whose period is a half of the ordinary grating. The depth of the extraordinarygrating is a half of the ordinary grating’s. The extraordinary grating formed at themiddle of each bulge of the ordinary grating and was attributed to the higher-ordermodulation arising from second-harmonic generation (SHG) of the femtosecond laserpulse incident to the surface of silica glass.When a single shot of three pulses interfered with each other, the two-dimensional periodic microstructure have been obtained, which distributed as a hexag-onal lattice. We also analyzed the microstructure by atomic force microscopy(AFM),and the analyzed results showed that the period accorded with the calculated result bythe equation very well. Diffraction pattern of the microstructure has been observedwith a laser beam at wavelength of 400 nm. The experimental results show that thefabricated microstructure can be utilized as a multi-beam-splitter. And the first order diffraction efficiency is up to 16.42% nearly. The morphology of the structures couldbe changed when the energy of the pulse was changed. The microvoid can be formedon the surface of the silica glass when the energy of the pulses is higher, on the otherhand, the orbicular platform of the microstructure can be observed. We propose anovel theoretic model to interpret the experimental results. The formation of the dif-ferent microstructures in our experiments can be attributed to the combined action oflight pressure to the induced plasma and the Marangoni effect to the molten liquid onthe surface of the bulk silica glass at different energy level of the pulse.Propose a novel method for generating optical vortex, and realize Super-position of orbit angular momentum of photons. We introduce a novel method togenerate the optical vortex with computer-generated hologram (CGH) fabricated in-side glass by femtosecond laser pulses. The CGH was directly written inside glass byfemtosecond laser pulses induced microexplosion without any pre- or post-treatmentof the material. We also realized the restructured optical vortex beams of both thetransmission and reflection pattern with high fidelity using a collimated He–Ne laserbeam. The total diffractive efficiency of both the transmission and reflection patternis about 4.79%.A novel method to realize the superposition of orbit angular momentum (OAM)of photons has been proposed by combined computer-generated hologram (CCGH)fabricated in silica glass with femtosecond laser pulses. Firstly, the two CGH of op-tical vortex (OV) were obtained and combined as a CCGH according to the design.Then the CCGH was directly written inside glass by femtosecond laser pulses. Thevortex beams with different vortex topological charges (including new topologicalcharges) have been restructured using a collimated He-Ne laser beam incidence to theCCGH normally. Theoretical and experimental explanations have been presented forthe generations of the new topological charges.Realize optical storage on the metal Film with the aid of the computer-generated hologram (CGH). The interaction between the femtosecond laser and themetal film has been studied in theoretic and experiment. When the femtosecond pulseinteracted with the Au film, the morphology of the ablated area is changing with theenergy of the pulse. If the energy of the pulse is large enough, we can get an ablatedvoid on the surface of the metal film. while the energy of the pulse is small enough,the nanocone could be attained on the surface of the metal film. When the femtosec- ond pulse interacted with the Al film, not only did we get the voids on the surface ofthe metal film, but we obtained the nanostructure on the surface of the substrate glass.It may offer a novel method for nanofabrication.Optical information has been stored on the metal film by femtosecond laserpulses with the aid of the computer-generated hologram (CGH). The Fourier transformof an object is performed by a computer, and then the resulted complex amplitude dis-tribution is encoded by the detour phase method. The resulted cell-oriented CGH isdirectly written on the metal film deposited on the glass substrate using near infraredfemtosecond laser by selective ablation. The object wave has also been restructuredwith high fidelity by using a collimated He-Ne laser beam.Fabricate volume grating in transparent glass by femtosecond laser pulsewriting directly. Femtosecond laser pulse with high energy could caused multiplemicroexplosion in the transparent materials, and there would be a relative long re-fracting index changing line formed in the direction of the pulse propagation. Theinteraction between the pulse with different energy or different number of the pulsesand the transparent glass have been studied, and we find different microexplosionviods array in the glass. When the energy of the pulse reaches to 20μJ, the refractingindex changing line arrive at 160μm. It could be used for fabrication of the volumegrating. The diffraction efficiency of the grating is changing with the fabricating con-dition which are different energy of pulse and different scanning velocity. We give aconcrete interpretation to the physical mechanism of the diffraction efficiency trans-formation.更多还原