有振幅调制光束经锯齿光阑的衍射特性

用惠更斯-菲涅耳衍射积分对有振幅调制光束经锯齿光阑的衍射作了研究,并与经圆孔硬边光阑的衍射作了计算比较.另外讨论了锯齿光阑参数对有振幅调制光束衍射特性的影响.结果表明,锯齿光阑有较大的填充因子,能抑制轴上光强的衍射调制,并降低横向光强分布的不均匀性.     

贝塞尔-高斯光束通过圆孔与圆环光阑的衍射

为了研究贝塞尔-高斯光束通过圆孔硬边光阑和圆环光阑的衍射特性,从Collins公式出发,采用数值模拟的方法模拟出光强分布.模拟结果表明,贝塞尔-高斯光束经圆孔光阑衍射后轴上光强随菲涅耳数F呈周期振荡;贝塞尔-高斯光束经圆环光阑后轴上光强随F呈振动衰减.在F相同时,贝塞尔-高斯光束经圆孔光阑衍射后横向光强分布比经圆环光阑衍射后横向光强分布平滑,孔径越小,光强调制越明显;当孔径与束腰相等时候,横向光强分布与菲涅耳数没有关系.     

齿形光阑聚焦特性的研究

采用一种简单有效的方法,模拟了光束经圆形孔径和不同齿形光阑的远场衍射分布,并与经圆孔硬边光阑的衍射作了比较.另外,讨论了齿形光阑的参数对光束衍射特性的影响.结果表明,齿形光阑能有效抑制光强的高频衍射,并降低横向光强分布的不均匀性.     

几类高斯光束通过超高斯光阑衍射的研究

为了研究贝塞耳-高斯光束、空心高斯光束,平顶高斯光束通过超高斯光阑的衍射特性,本文从collins公式出发,采用数值模拟的方法,得到衍射光强的分布结果.模拟结果表明当菲涅尔数为4时候,衍射出现无调制现象,该种光阑有效的抑制了光强的衍射.当菲涅尔数确定时候,空心高斯光束在横截面上衍射光强的分布较为平滑.     

小尺寸波纹光阑的实验研究

报道了在光路中使用小尺寸波纹光阑代替圆孔光阑的研究结果。应用菲涅耳衍射光强分布理论以及光上光强分布理论对波纹光阑在一定条件下的作用范围进行了分析。用CCD成像系统对实验结果进行记录。结表明实际与理论能较好地吻合。从光路的实际使用效果看，对比圆孔光阑，应用波纹光阑在其作用范围内实现了对光束衍射调制的抑制和填充冈子的提高。     

激光束的实时空间整形方法

在高功率激光系统中,激光光束的传输与放大,需要对输出的激光光束整形,包括对激光束几何形状与光强分布的整形,才能有效地控制光束质量,提升激光系统的输出功率。目前,通常的光束空间整形方法是采用针对特定输入光束(如均匀或高斯光束)的切趾光阑(如锯齿、波纹光阑)或结合空间滤波进行光束空间整形,而实际输入的光束并非是这样的理想型光束,所以上述方法在光束的空间整形中存在一定局限性,因此,研究实时、可调的光束空间整形尤为重要。对此,本文提出了对激光束进行实时、可调控的激光束空间整形的新方法,实时产生与入射光束相关的软边切趾光阑,结合空间滤波,获得所需形状的近"平顶"光强分布的近场光束。数值模拟结果表明新方法可以对实际激光系统的光束实现实时、有效的整形。     

硬边光阑、超高斯光阑和锯齿光阑的比较研究

以复宗量拉盖尔—高斯(ELG)光束为例,对ELG光束经硬边光阑、超高斯光阑和锯齿光阑的衍射特性作了详细的比较研究。数值计算结果表明,超高斯光阑和锯齿光阑的优点是能有效抑制菲涅尔衍射调制并有较大的填充因子。     

平顶高斯光束及其通过圆孔光阑的衍射

为了研究平顶高斯光束通过圆孔硬边光阑衍射特性,本文从collins公式出发,采用数值模拟的方法,模拟结果表明平顶高斯光束在阶数大于10以后,光强的分布变化不大.平顶高斯光束经过圆孔衍射,孔径大时光强在横截面调制越厉害,但是强度小;孔径小时光强在横截面调制相对小,但是光强度相对大.轴上光强分布在孔径大时随菲涅耳数增大出现增大现象;孔径小时光强在轴上分布随菲涅耳数出现周期性振荡的调制特性.     

光阑对非均匀偏振光传输特性的影响

从光束的相干-偏振(BCP)矩阵和传输理论出发,推导出了非均匀偏振(NUP)光通过光阑后的偏振度和光强分布的一般表示式。给出了一个光强均匀分布NUP光束的数值计算例。结果表明,通过光阑后光束的偏振度和光强分布发生了显著的变化。横平面上偏振度出现了振荡,光强剖面为非均匀分布。但在远场为均匀偏振。     

平顶高斯光束通过光阑-透镜分离系统的焦移

为了对平顶高斯光束通过光阑-透镜分离光学系统轴上光强分布和焦移进行详细研究,采用Collins公式,通过数值计算,对各个参量对光强分布和焦移的影响进行了分析,得到了精确直观的解析式。结果表明,其光强分布和焦移不仅由平顶高斯光束的阶数N、光束的菲涅耳数Fw决定,还与光阑菲涅耳数Fa、光阑与透镜距离s有关。     

波前像差对超短飞秒激光脉冲聚焦特性的影响

为了研究波前像差对超短飞秒激光脉冲聚焦特性的影响, 基于瑞利-索末菲标量衍射理论, 对比研究了在散焦、像散、慧差、三叶形像差以及球差等各类波前像差下, 均匀强度分布和高斯强度分布的超短飞秒激光脉冲的聚焦特性。结果表明, 波前像差对均匀强度分布的飞秒脉冲在焦平面处的光强分布具有明显的不利影响, 从而降低飞秒脉冲的聚焦峰值功率, 而对高斯强度分布的飞秒脉冲影响相对较小, 即在高斯强度分布下, 在焦平面处仍然有可能获得较好的、近衍射极限的聚焦光斑; 在非焦平面处, 即使初始脉冲具有高斯强度分布, 非焦平面处的光强分布受各类波前像差的影响也较为明显; 对于所研究的30fs(1/e2半宽度)超短脉冲, 波前像差对脉冲持续时间的影响几乎可以忽略。此研究结果对超短飞秒激光束的光束质量评估及聚焦特性分析具有实际的指导意义。     

利用波纹光阑和空间滤波器改善光束近场分布

详细研究了波纹光阑的菲涅耳衍射特性，提出并论证了利用波纹光阑和空间滤波器的结合使用能进一步有效地改善光束近场分布、抑制光束总体的衍射调制、提高光束填充因子。     

Time Domain Analysis of the Near-Field Radiation of Shaped Electrically Large Apertures

The near-field radiation of several electrically large apertures has been computed based on the aperture field convolution method, including a square aperture, a circular aperture, and a serrated edge aperture. The frequency range is 8.0–12.0 GHz. The aperture diameters are limited to 5.00 m and the corresponding electrical size is 133–200 wavelengths. The time domain spectrum has been obtained by chirp z-transform with a Hamming window and the mechanism for the generation of the aperture near-field radiation in time domain is analyzed. The calculation results demonstrate that the near-field radiation of the aperture can be approximately seen as the synthesis of a plane wave from the aperture, cylindrical waves from the edges, and spherical waves from the corners. By this method, the direction, position, and magnitude of incoming waves in the near-field region can be estimated, and the aperture design can be modified to meet the requirements of the near-field radiation. The near field of the three apertures mentioned above has been compared, and it is shown that the serrated edge aperture has more uniform direct wave and lower diffraction waves, making it a candidate for compact range (CR) aperture design.      

Experiments on improved unstable mode profiles by aperture shaping

A 3.5-μm He-Xe laser has been used to experimentally observe improvements in mode intensity profiles by shaping the cavity aperture. Significant improvements over circular apertures were achieved with elliptical and serrated mirror shapes.     

Compact range reflector analysis using the plane wave spectrumapproach with an adjustable sampling rate

An improved method for determining the test zone field of compact range reflectors is presented. The plane wave spectrum (PWS) approach is used to obtain the test zone field from knowledge of the reflector aperture field distribution. The method is particularly well suited to the analysis of reflectors with a linearly serrated rim for reduced edge diffraction. Computation of the PWS of the reflector aperture field is facilitated by a closed-form expression for the Fourier transform of a polygonal window function. Inverse transformation in the test zone region is accomplished using a fast Fourier transform (FFT) algorithm with a properly adjusted sampling rate (which is a function of both the reflector size and the distance from the reflector). The method is validated by comparison with results obtained using surface current and aperture field integration techniques. The performance of several serrated reflectors is evaluated in order to observe the effects of edge diffraction on the test zone fields     

Estimating aperture efficiency

It is shown that for a wide class of aperture distributions, the aperture efficiency can be related to the ratio between the beamwidth of this distribution and that of the uniform one. A heuristic rule for estimating the aperture efficiency of elliptic and rectangular tapered apertures is introduced. It is shown that, if the beamwidth is given (i.e., the aperture size is unconstrained), the maximum directivity is provided by a tapered, rather than uniform amplitude distribution.