The Study on Volume Holographic Diffraction of Ultrashort Pulsed Laser beams

本论文的写作目的是全面系统的研究超短激光脉冲体全息衍射的特性及其可能的应用。 随着超短激光脉冲产生技术的发展，其体全息衍射的性质以及在光通信和光信息处理等领域中的应用最近引起了人们的重视，而成为当前研究的热点问题之一。但已有研究并没有给出体全息光学元件的局域尺寸，记录和读出光束的偏振状态以及记录材料的各向异性等条件对超短激光脉冲的全息衍射性质的影响，因而并不全面实用。体全息光栅是一种最简单也是应用最广泛的体全息光学元件。本论文以此为例，在耦合波理论的基础上，从全结构、全偏振方面，更加全面系统的研究了各种偏振状态的超短激光脉冲通过不同结构的体全息光栅衍射的时空分布特性，探索了基于体全息光栅的集成化光学器件在超短超快光学的脉冲滤波整形方面的应用。 论文首先综述了超短激光脉冲的产生、整形原理、测量技术和经简单光学元件衍射性质的研究现状，系统的介绍了体全息光栅的衍射理论，记录材料和应用领域，然后在给出了本论文的创新性研究成果，主要包括： （1）对光栅输人输出面尺寸远大于光栅厚度的平面无限大体全息光栅，拓展一维标量和矢量耦合波理论，研究了超短激光脉冲体全息衍射的光栅参量调制特性、偏振依赖特性和脉冲滤波整形特性，提出了一种脉冲滤波整形的装置。 论文给出在色散效应的影响下，出射脉冲光束的强度分布和总衍射效率受光栅参量调制的特性，并给出了入射脉冲的光谱宽度与光栅的光谱宽度比值不同时的结果，还将透射型和反射型体全息光栅进行了比较。论文接着给出了垂直和平行两种偏振状态的超短激光脉冲的衍射性质的异同，并讨论了偏振态任意的超短激光脉冲入射时，衍射性质的偏振调制的脉冲滤波整形特性。论文还设计提出了一种可以实现脉冲滤波整形的装置，分析了该装置的基本原理，具体实施方式及技术效果。 （2）对二维有限尺寸的局域体全息光栅，首次拓展二维耦合波理论，研究了光栅局域尺寸效应对超短激光脉冲体全息衍射时空分布性质的影响，并提出了改善出射脉冲光束的时空分布和光束质量的方法。 论文以完全重叠型的局域体全息光栅为例，给出了衍射和透射激光脉冲的强度沿光栅出射边界在频谱空间域和时间空间域分布的闭形式理论解，定义了局域体全息光栅的光谱宽度和总衍射效率，结合数值研究分析了光栅的局域尺寸效应在光栅参数和入射脉冲宽度不同时，对出射激光脉冲强度时空分布和光栅的总衍射效率的空间分布的影响。与一维体全息光栅对超短激光脉冲衍射的性质作比，给出了合理选择局域体全息光栅的尺寸，以在光栅出射边界上得到总衍射效率较大且分布较均匀的衍射光脉冲的方法。 （3）对记录于各向异性晶体中的偏振局域体全息光栅，首次在三维矢量耦合波理论的基础上，全面系统的研究了光栅偏振局域尺寸效应对超短激光脉冲体全息衍射性质的影响。研究综合考虑了记录和读出光束的偏振状态，体全息光栅的局域尺寸，记录介质的色散效应和光学各向异性等因素对衍射性质的影响，以记录于光折变各向异性铌酸锂晶体中的局域体全息光栅为例，给出了出射激光脉冲的时空分布和衍射效率在光栅出射边界上的空间分布以及总衍射效率随体全息光栅的记录和读出条件的变化而变化的趋势，并将这一结果与连续光读出此光栅和超短激光脉冲读出平面无限大体全息光栅的研究结果进行了比较。The goal of this work is to investigate the diffraction characteristics of ultrashort pulsed laser beams (UPBs) by volume holographic optical elements. With the remarkable progress of the technique to generate UPBs, the diffraction of them by volume holographic optical elements are of wide interests in applications of them in fields ranging from Optical communication to Optical Information Processing, and has become a hot topic these days. However, the previous studies are not comprehensive and practical since the effects of the finite size and the polarization states of the recording and reading beams of the optical elements, the dispersion and the optical anisotropic of the recording material on the diffraction properties, which should be taken into account in their practical applications. Among the volume holographic optical elements, volume holographic gratings (VHGs) have the flexibility and the possibility of using them to implement dynamic processing, we, in this thesis, systematically study the diffraction properties of the UPBs diffracted by the VHGs, based on the coupled wave theory, and explore the possibilities of its applications in ultrashort laser pulses filtering and shaping. After a brief introduction about the UPBs and VHGs in section 2, the original work of the thesis is presented, it mainly includes: (1) For the planar infinite VHGs where the area of the entrance and exit surfaces (corresponding to the transverse apertures of the incident and diffracted beams, respectively) are much larger than the grating thickness, the properties of UPBs diffracted by them are systematically studied based on the developed one-dimensional scalar and vectorial coupled wave theory, with considering a combined effect including the material dispersion and anisotropic properties, the grating parameters, the polarization state and the pulse width of the input UPB. A corresponding pulse shaping devise is proposed, which can be used in the real-time pulse shaping application. The effects of the grating parameters on the spectral and temporal distributions of the diffracted and transmitted signals and the total diffraction efficiency are firstly investigated when the ratios of the spectral bandwid of the input UPB to the spectral bandwidth of the grating have different values. And then, the polarization-dependent and pulse filtering and shaping properties of the diffraction are systematically analyzed. Comparison of the diffraction properties of transmission and reflection VHGs by the UPB is presented. And a new method of filtering and shaping of UPBs by VHGs is proposed. The corresponding device is designed, which can be used in real-time pulse shaping application. (2) The effect of the geometrical size of the finite sized volume holographic optical elements on the spatial and temporal diffraction properties of the UPB is firstly analyzed using the extended two-dimensional coupled wave theory since the size of the volume grating in contemporary applications is restricted. The method of improving the beam quality is given. As to a spetial case of the overlapping grating, after defining the spectral bandwidth and total diffraction efficiency of the grating, the spatial and temporal distributions of the transmitted and diffracted pulsed beams and the spacial distribution of the diffraction efficiency are shown theoretically and numerically. (3)The polarization-dependent diffraction properties of a UPB by a finite sized anisotropic VHG are firstly investigated based on the developed three-dimensional vectorial coupled wave theory. The combined effects of the polarizations of the recording and readout beams, the grating geometrical size, the dispersion and the optical anisotropic of the crystal, the recording angle and the space-charge field on the properties are taking into account. The polarization-dependent spectral bandwidth of the finite sized VHG is analyzed. It determines the intensity distributions of the transmitted and diffracted pulsed beams along the output face of the VHG. The distortion and wideness of the diffracted pulsed beams are different for the different points on the output face of the grating, as numerically shown for the finite sized VHG recorded in LiNbO3 crystals. The beam quality is also analyzed. The variations of the total diffraction efficiency are shown with the geometrical size of the grating and the temporal width of the readout UPB. In addition, comparison of the diffraction properties between the finite sized and one-dimensional VHG for pulsed and continuous wave readout is drawn. The study is of great benefit to the applications of VHGs and UPBs