Optimization of Axial Intensity Point Spread Function

It is known that for the converged laser beam, the axial intensity distribution corresponds to a Gaussian curve, that is, the intensity on the focal plane is the peak intensity. When it defocuses, the intensity would decrease rapidly. In optical data storage, for instance, we expect the intensity within a certain distance to be almost equal. In this paper, we propose to use a pure phase superresolution apodizer to optimize the axial intensity distribution of the converged laser beam and at the same time improve the resolution. The intensity point spread function remains almost identical in a wide range within the focal depth.     

部分相干平顶高斯光束通过球差透镜的聚焦特性

 基于部分相干光的传输理论，研究了部分相干平顶高斯光束通过球差透镜聚焦后轴上点的光强分布。数值计算表明:轴上最佳聚焦点随着球差从负到正的变化而向几何焦点方向移动；光束阶数越大，实现最佳聚焦点越过几何焦点所需的正球差值越小；正负球差对应的最佳聚焦点始终分居于无球差时最佳聚焦点的两侧;轴上最佳聚焦点的光强随着球差从负到正的变化而变小；当正负球差绝对值较大时，光强随球差的变化较为缓慢，而在球差值为0附近，光强随球差的变化比较剧烈。     

Lens axicon illuminated by polychromatic Gaussian beams for generating uniform focal segments

In this paper, we investigate a lens axicon, which actually is a lens with spherical aberration, illuminated by a polychromatic Gaussian beam for producing an extended axial line image of a desired length and nearly uniform intensity. A numerical calculation is performed to investigate the dependence of the axial intensity distribution of the focal segment on the parameters of the incident polychromatic Gaussian beam. It is shown that, compared with monochromatic Gaussian beam illumination, the illumination of the polychromatic Gaussian beam may improve the uniformity of the distribution of the axial intensity, and this improvement in the uniformity of the axis intensity is strongly dependent on the spectral width of the incident Gaussian beam. Moreover, apodization with annular super-Gaussian amplitude distribution is employed to reduce the undesired oscillation of the axial intensity.     

Axicons用于光学超分辨

提出了用圆锥棱镜构建光束整形器.该器件能将圆形光束转换成环形光束,由它所产生的环形光束的直径是可调的,即系统超分辨效应具有可调节性.给出了理论分析和数值模拟,模拟结果表明此器件可以实现光学超分辨,改变几何参数可以调节超分辨效应.     

根据激光束横截面能量分布的变化测量大功率激光聚焦镜的像差

提出了一种实时测量大功率激光照射下聚焦镜产生的像差的新方法。该方法利用混合模激光束在传输过程中光束横截面能量分布的变化来进行测量。首先通过计算混合模激光束的光学参数来模拟其在传输过程中的光束横截面能量分布的变化,然后计算其通过聚焦镜后在焦点位置的光束横截面能量分布,通过对比计算所得的光束横截面能量分布和实际测量的焦点位置的光束横截面能量分布的差异,得到聚焦镜的像差。     

拉盖尔-高斯光束通过光阑-透镜分离系统的聚焦特性和焦移

 使用Collins公式推导了拉盖尔-高斯光束通过光阑-透镜分离系统的光强分布。利用数值计算详细分析和说明了其聚焦特性。分析得出光阑-透镜分离程度的大小影响相对焦移的大小和光强的分布，并引起焦移可能相反或消失。而且发现满足一定条件时在一段较大的轴向距离上光强几乎等于光强极大值，从而可获得一个较大的光强极大范围。     

非傍轴径向阵列高斯激光束的传输特性

推导出相干和非相干非傍轴径向阵列高斯激光束的传输公式,并用以研究了径向阵列光束在自由空间的传输特性,重点分析了阵列光束参量对合成光束光强分布的影响。结果表明:阵列半径与束腰宽度之比是一个关键参量,当它固定时,相干和非相干合成光束的光强分布都保持不变,但合成光束的光强分布和远场轴上光强最大值都与合成方式有关。     

焦斑二阶矩半径与光束近场分布的关系

为分析光束振幅畸变和相位畸变对其焦斑二阶矩半径的影响,以光波标量衍射理论中的夫琅和费衍射公式为基础,根据光斑二阶矩半径的定义,推导了直接依赖于光束近场复振幅分布的焦斑二阶矩半径的一般表达式,并进一步推导了直接依赖于光束近场强度分布和相位分布的焦斑二阶矩半径和焦斑二阶矩角半径的表达式.结果表明:畸变光束的焦斑二阶矩角半径...     

部分相干光束照射的透镜轴棱锥获得均匀焦线

从部分相干光的交叉谱密度函数传输公式出发,推导了高斯谢尔模型(GSM)光束被球差透镜衍射后轴上光强分布的解析公式,并进行了数值模拟和物理分析。结果表明,具有一定束腰宽度和空间相干度的GSM光束经过负球差透镜聚焦后,可以获得轴上光强的均匀分布。通过改变GSM光束的束腰宽度和空间相干度来实现轴上光强均匀分布的方法很简单,转换效率高。     

亚微米局域空心光束的产生及其在单原子囚禁与冷却中的应用理论研究

提出了一种采用单模光纤、环形二元相位板和微透镜组成的光束整形系统产生亚微米局域空心光束的方案. 根据瑞利-索莫菲衍射积分公式, 数值计算了微透镜焦平面附近的场分布, 详细研究了空心光束的暗斑尺寸与单模光纤模场半径和微透镜焦距的关系. 数值计算结果表明: 在微透镜焦平面附近光场分布近似对称, 在焦点处场强近似为零, 周围场强逐渐增大, 形成半径约为0.4 μm的三维封闭的球形空心光场区域, 即亚微米局域空心光束. 当局域空心光束为蓝失谐时, 光场中的原子将被囚禁在光场最弱处. 若加上抽运光, 原子将受到蓝失谐局域空心光束与抽运光共同激发的强度梯度Sisyphus冷却. 本文利用该方案产生的亚微米局域空心光束构建单原子的囚禁与冷却器件, 并以单个⁸⁷Rb原子为例, 利用Mont-Carlo方法研究亚微米局域空心光束中单原子囚禁与强度梯度冷却的动力学过程, 结果表明利用该器件可以获得温度在5.8 μK量级的超冷单原子.     

离轴径向偏振光束及其传输特性

基于Wolf近轴传输理论, 导出离轴径向偏振光束光强的解析表达式, 并研究离轴量对离轴径向偏振光束传输中光强分布的影响, 同时根据一阶矩质心位置的定义推导出离轴径向偏振光束的质心坐标, 研究其质心位置的变化规律. 结果表明, 与径向偏振光束不同, 离轴径向偏振光束在近场处传输时光强分布不均匀, 随着传输距离的增加, 光强分布均匀性逐渐得到改善, 而径向偏振光束在传输中始终保持空心对称光斑. 离轴量较小时, 近场处光强分布呈非对称空心面包圈形, 随着传输距离增达到一定程度, 光强分布演化为对称空心面包圈形, 离轴量越小, 演变距离越短; 离轴量较大时, 随着光束的传输离轴径向偏振光束的空心部分消失, 逐渐由空心面包圈形向高斯型演变, 径向偏振光束特性消失. 另一方面, 离轴径向偏振光束的质心不随传输距离的改变而改变. 质心纵坐标恒为零, 质心横坐标与光斑尺寸及离轴量相关. 随着光斑尺寸增大, 质心横坐标成线性增长. 当离轴量较小时, 质心横坐标随离轴量的增大呈非线性增长, 增长量不明显; 离轴量较大时, 质心横坐标随离轴量的增大呈线性增长, 且变化明显.     

Cylindrical vector axisymmetric Bessel-modulated Gaussian beam

Focusing properties of the cylindrical vector axisymmetric Bessel-modulated Gaussian beam with quadratic radial dependence (QBG beam) in high numerical aperture system is investigated theoretically by vector diffraction theory. Results show that intensity distribution in focal region can be altered considerably by beam parameter μ and polarization angle. Polarization angle may adjust transverse intensity distribution, for instance from one focal spot to one ring shape. While μ alters axial intensity distribution remarkably, focal splitting may occur with tunable focal shift, and real value μ also may induce local intensity minimum. For certain case, with increasing imaginary value μ, transverse focal spot shrinks accompanied with higher full width half maximum of axial intensity distribution.     

Diagnostic system for two dimension intensity distribution of laser beam

The diagnostic system for two dimension(2-D)intensity distribution of laserbeam is a measuring instrument for many parameters of laser beam.2-D intensity distributionplot of laser beam is obtained by the two dimension scanning mirror which is controlled by amicrocomputer to scan the laser beam on a detector.Many parameters of laser beam such asthe isointensity distribution plot,the beam diameter,the beam waist diameter,the laser pow-er,the diverge angle and the beam brightness,are given by means of the microcomputer pro-cessing the data measured.Theoretical analysis of beam parameter transform is given.     

平顶飞秒激光经圆锥透镜在熔融石英中成丝及超连续辐射

实验研究了平顶飞秒激光经圆锥透镜后在熔融石英中的成丝及超连续辐射.与高斯飞秒激光的成丝对比发现,平顶飞秒激光可以获得在圆锥透镜焦深区域内强度分布更为均匀的等离子体细丝,这一特征更有利于飞秒激光在固体介质中进行微纳加工等领域的应用.并且,在不损伤熔融石英的条件下,平顶飞秒激光成丝可以获得更高能量、更高转换效率的超连续辐射,这是因为若产生光强相近的细丝,平顶飞秒激光所需的初始激光能量更高,此激光能量下产生的细丝长度更长、均匀性更好.     

Tight focusing effect of annular obstructed incident beam in the focal region of high NA lens

Focusing properties of the azimuthally polarized axisymmetric Bessel-modulated Gaussian beam with Quadratic Bessel Gaussian (QBG beam) and annular aperture are investigated theoretically by vector diffraction theory. Simulation results show that the intensity distribution in focal region of the azimuthally polarized axisymmetric QBG beam can be shifted along optical axis considerably by changing parameter (C). On introducing annular aperture (δ), focal pattern at the focus extends along optical axis. In this paper, we have shown the generation of focal hole and focal shifting in the axial direction of incident beam propagating through aligned optical system which is suitable for application such as optical manipulation and optical trapping.     

用远场法研究自由旋气动窗口的光学特性

 采用He-Ne激光,对穿过自由旋气动窗口的远场聚焦光斑进行图象采集和数据处理,研究本气动窗口对透过其输出通道的激光束所带来的偏转和随机抖动现象,计算分析气动窗口对激光束发散特性的影响,定义和实验研究气动窗口的光束质量β因子。同时,分析讨论气动窗口对激光束远场聚焦光斑光强分布的影响,并提出气动窗口光束质量和气动窗口设计的进一步研究思路。     

Design, simulation and application of phase plates

In this paper we analyze the use of phase plates to obtain homogeneous laser intensity profiles. We studied the dependence of intensity distribution on phase plates characteristics, we obtained analytical solution for the intensity profile in the focal plane for plane waves and developed a numerical simulator to calculate the intensity distribution with a generic initial beam and at any propagation plane. We defined criteria to evaluate the quality of profiles produced by different phase plates. Finally we compared experimental results obtained at the Max-Planck Institut für Quantenoptik of Garching with our numerical simulations. Received 23 July 2001 and Received in final form 8 January 2002     

Focus evolution of Gaussian beam induced by phase plate

In this article, vector diffraction theory is employed to investigate the focusing properties of the Gaussian beam through a phase plate. The phase plate may alter the wavefront phase of an incoming beam by topological charge. Both the circular phase distribution and the annular phase distribution plates are investigated. Numerical simulations show that the focal intensity distribution depends on topological charge. With changing topological charge, focal intensity distribution may evolve into ring shape, and some novel focal spots may occur. Focal intensity distribution evolving process with integer topological charge differs considerably from that with fraction topological charge. When the concentric annular phase plate is placed in the laser path, the focal intensity distribution depends on both the inner radius and topological charge. For small inner radius of the phase plate, doughnut-shape focal pattern occurs. With increasing inner radius, the diameter of the doughnut focal pattern decreases, and doughnut shape disappears slowly in some cases.     

The effect of spherical aberration on temperature distribution inside glass by irradiation of a high repetition rate femtosecond pulse laser

In this paper, we study the effect of spherical aberrations on the light intensity and the temperature distribution in the focal region in a 250-kHz femtosecond laser irradiated Ag⁺-doped borosilicate glass. When a focused beam goes through an interface between air and glass, spherical aberration will result in the separation of the focal point and then cause a clear change of the light intensity distribution along the incident direction. That phenomenon will further influence the longitudinal cross-section temperature distribution in glass. Here we use Ag nanoparticle formation as a marker for establishing temperature distribution and we find that the formation of nanoparticle shows a strong dependence on the temperature field and the detailed precipitation process is also discussed.     

Fabrication of a binary diffractive lens for controlling the luminous intensity distribution of LED light

To control the luminous intensity of an light-emitting diode (LED), we designed and fabricated a binary diffractive lens by electron beam lithography on a poly(ethylene terephthalate) (PET) film. We showed that it is possible to control luminous intensity distribution using the binary diffractive lens. To improve the diffraction efficiency, we then designed a binary blazed diffractive lens with a focal length of 140 mm. With a binary blazed diffractive lens having a focal wavelength of the order of micrometers, it is possible to create a small, thin light source for controlling the distribution of luminous intensity.