Spectral anomalies of pulsed Hermite-cosh-Gaussian beams focused by an aperture lens

The spectral behaviors of pulsed Hermite-cosh-Gaussian (HChG) beams focused by an aperture lens are studied. The propagation equation for the power spectra of pulsed HChG beams focused by an aperture lens is derived and used to study the spectral anomalies of pulsed HChG beams in the focused field. Numerical results are given to illustrate the dependence of spectral anomalies behavior on the pulse parameter and truncation parameter. The potential applications of spectral anomalies of ultrashort pulsed beams in information encoding and information transmission are considered.     

Spectral anomalies of diffracted pulsed Bessel beams in dispersive media

Starting from the Huygens–Fresnel diffraction integral, the analytical expression for the power spectrum of diffracted pulsed Bessel beams in a dispersive media is derived and used to study the spectral anomalies of pulsed Bessel beams in the far field. Numerical results are given to illustrate the dependence of the anomalous spectral behavior on the pulse parameters, aperture parameter and dispersive properties of the medium. It is shown that, near phase singularities, anomalous spectral behavior may take place. The potential applications of spectral anomalies of ultrashort pulsed beams in information encoding and information transmission are considered.     

高阶贝塞尔脉冲光束通过色散光阑透镜的传输特性*

研究了高阶贝塞尔脉冲光束通过色散光阑透镜的光谱和时间空间特性.结果表明:脉冲光束在几何焦面上会出现光谱开关,透镜色散使产生光谱开关的临界位置向z轴移动|透镜一阶色散使几何焦面上峰值光强减小,并使脉冲波形产生显著时间移动和展宽,而二阶和高阶色散的影响较小.此外,光束阶数n和空间参量α也会影响横向光强分布.     

高阶贝塞尔脉冲光束通过色散光阑透镜的传输特性

研究了高阶贝塞尔脉冲光束通过色散光阑透镜的光谱和时间空间特性.结果表明:脉冲光束在几何焦面上会出现光谱开关,透镜色散使产生光谱开关的临界位置向z轴移动;透镜一阶色散使几何焦面上峰值光强减小,并使脉冲波形产生显著时间移动和展宽,而二阶和高阶色散的影响较小.此外,光束阶数n和空间参量α也会影响横向光强分布.     

Spectral anomalies of pulsed Hermite-Gaussian beams in Young’s interference experiment in dispersive media

Starting from the Huygens-Fresnel diffraction integral, the recurrence expression for the power spectra of pulsed Hermite-Gaussian beams in Young’s interference experiment in dispersive media are derived and used to study the spectral anomalies of pulsed Hermite-Gaussian beams in the far field. The results of numerical calculation are given to illustrate the dependence of spectral anomalous behavior on the pulse parameter, slit parameter, diffraction angle and dispersive property of medium. The potential application of spectral anomalies of pulsed Hermite-Gaussian beams in information encoding and information transmission in dispersive media is considered.     

Spectral anomalies of diffracted pulsed Hermite--Gaussian beams in dispersive media

This paper derives and uses the recurrence expressions for the power spectra of diffracted pulsed Hermite-Gaussian （HG） beams in dispersive media to study the spectral anomalies of pulsed HG beams in the far field. Numerical results are given to illustrate the dependence of spectral switches on the pulse parameters, truncation parameter and dispersive property of the medium. The potential application of spectral anomalies of ultrashort pulsed beams in information encoding and transmission is discussed.     

被光阑像散透镜聚焦高斯-谢尔模型光束轴上的光谱开关

从部分相干光的传输理论出发,研究了高斯-谢尔模型光束通过光阑像散透镜聚焦的光谱异变和光谱开关。研究表明,在考虑像散的情况下,聚焦场轴上也会出现光谱异变和光谱开关。光谱异变和光谱开关不仅与空间相关性、截断参量、菲涅耳数和源光谱谱宽有关,透镜像散对光谱异变和光谱开关也会产生影响。通过数值计算结果,重点对透镜像散对光谱移动和光谱开关的影响进行了分析。与无像散情况相比,像散会使出现光谱开关的临界位置发生变化,当像散较大时出现光谱开关的临界位置明显向几何焦面移动,特别是当像散增加到一定数值时,光谱开关会消失。     

Spectral anomalies of diffracted pulsed Hermite-cosh-Gaussian beams in dispersive media

Starting from the Huygens–Fresnel diffraction integral, the analytical expressions for the power spectra of diffracted pulsed Hermite-cosh-Gaussian (HChG) in dispersive media are derived and used to study the spectral anomalies of pulsed HChG. Numerical results are given to illustrate the dependence of spectral anomalies behavior on the decentered parameter, truncation parameter and dispersive property of the medium. The potential applications of spectral anomalies of ultrashort pulsed beams in the information encoding and information transmission are considered.     

Spectral properties of spatially and spectrally partially coherent cosh-Gaussian pulsed beams focused by an aperture lens

The analytical expression for the spectrum of spatially and spectrally partially coherent cosh-Gaussian pulsed (ChGP) beams focused by an aperture lens is derived and used to study their spectral properties at the focal plane and on the axis. The effect of the truncation parameter, spatial correlation parameter, decentered parameter and temporal coherence length on the spectral shifts and spectral switches of spatially and spectrally partially coherent ChGP beams is stressed. The results are illustrated numerically and interpreted physically.     

Multiscale Bessel beams generated by a tunable acoustic gradient index of refraction lens

A beam that resembles a Bessel beam on two scales is generated using a tunable acoustic gradient index of refraction (TAG) lens. The minor scale of the TAG-generated Bessel beam is nondiffracting and self-healing. The major scale of the beam diffracts while still forming a Bessel pattern due to the specific geometry of the TAG lens. The acoustic and optical theory behind the TAG lens is outlined, and the experimental beam itself is presented. The major and minor rings are explained, and the TAG beam is compared with both axicon-generated and conventionally focused Gaussian beams.     

On-axis spectral shifts and spectral switches of Gaussian Schell-model beams focused by an astigmatic aperture lens

Starting from the propagation law of partially coherent light, the on-axis spectral shifts and spectral switches of Gaussian Schell-model (GSM) beams focused by an astigmatic aperture lens are studied. It is shown that, as compared with an aberration-free case whose spectral shifts and spectral switches are induced by spatial correlation and aperture diffraction, the spectral shifts and spectral switches of GSM beams also depend upon the astigmatism of the lens for an astigmatism case. Detailed numerical calculations are made to illustrate the behavior of spectral shifts and spectral switches of GSM beams focused by an astigmatic aperture lens.     

聚焦部分相干涡旋光束的传输和相干特性

根据部分相干光的传输理论,研究了部分相干高斯 贝塞尔涡旋光束通过光阑透镜聚焦后的传输和空间相关性质.数值计算结果表明,涡旋暗核的大小和焦平面上的光谱相干度都取决于入射光的拓扑电荷n、截断参量δ、相对相干长度σg和参量α.当选择适当的参量,在几何焦点附近会出现局域空心光束.研究还发现在焦面上光谱相干度会产生一个或多个的相位奇点（相干涡旋）,而且拓扑电荷和相对相干长度会对相干涡旋的位置和个数产生影响.在相干极限下,相干涡旋可逐渐演变为光学涡旋.     

无衍射贝塞尔光束非球面透镜设计

提出一种可产生无衍射贝塞尔光束的非球面透镜-贝塞尔透镜,该透镜由球面和非球面组成,呈旋转对称结构。利用光学设计软件ZEMAX通过光线追迹法对贝塞尔透镜进行设计,在设计和优化过程中,将出射光线与光轴的夹角作为边界条件,二次曲线参量和高次项系数作为变量。结果表明:利用标准二次曲线加上第一个高次项就可以得到比较理想的优化结果,设计的非球面贝塞尔透镜可以产生具有贝塞尔光束特性的无衍射光束。     

高阶矢量光束高数值孔径聚焦特性的研究

本文利用Richards-Wolf矢量衍射积分模型对-2到4阶的贝塞尔型 矢量光束经高数值孔径聚焦后焦平面处的光强分布进行了理论仿真和特性研究, 并对矢量光束的聚焦场在真空下俘获玻璃小球的梯度力分布进行了仿真. 结果表明聚焦场的形状、尺度及各分量的变化与矢量光束的阶数有密切关系, 且具有特定的规律; 此外, 聚焦场的梯度力分布与矢量光束的阶数也有密切关系,并且具有多种不同形状和尺度的光陷阱.     

Dynamic pulsed-beam shaping using a TAG lens in the near UV

The ability to dynamically shape the spatial intensity profile of an incident laser beam enables new ways to modify and structure surfaces through pulsed laser processing. Here we describe a method to generate doughnut-shaped beams from an input Gaussian source using a tunable acoustic gradient index (TAG) lens. The TAG lens is capable of modulating between focused beams and annular rings of variable size, using sinusoidal driving frequencies. Laser micromachining is accomplished by synchronizing the TAG lens to a 355 nm pulsed nanosecond laser. Results in polyimide demonstrate the ability to generate adjacent surface features with different shapes and sizes.     

高斯-谢尔模型光束通过光阑像散透镜传输轴上光谱变化

从部分相干光的传输理论出发,研究了高斯-谢尔模型(GSM)光束通过光阑像散透镜传输轴上的光谱变化规律.结果表明,与光源光谱相比,高斯-谢尔模型(GSM)光束通过光阑像散透镜传输轴上光谱发生了中心频率的移动,这种现象被称为光谱位移.详细分析了透镜的像散、光束的空间相关性和光阑的截断参量对光谱变化的影响.数值计算表明,这些参量会对光谱移动产生比较大的作用.     

Spectral and spatiotemporal properties of Bessel–Gauss pulsed beams focused by a dispersive aperture lens

The spectral and spatiotemporal properties of Bessel–Gauss pulsed beams focused by a dispersive aperture lens are studied, where the dispersion of the first, second, and higher orders is taken into consideration. It is shown that the spectral switches take place at the geometrical focal plane, and the dispersion of the first order leads to a shift of the critical position towards the z-axis. The dispersion plays a noticeable role in the spatiotemporal intensity distribution. The dispersion of the first order results in a decrease of the peak intensity, in a shift and a broadening of the pulse form, and the effect becomes more noticeable with increasing waist width. The dispersion of the second order results in a further broadening and a decrease of the peak intensity, and the effect is larger as the thickness of the lens increases. However, the dispersion of the higher order plays a relatively minor role. The results are illustrated by numerical examples and interpreted physically.     

球差透镜聚焦部分相干光束获得局域空心光束

基于Collins公式,研究了空间相干度为零阶贝塞耳函数的部分相干光通过球差透镜后在几何焦平面附近的光强分布情况.研究表明,通过改变部分相干光的光谱相干度,球差系数可以得到平顶光束和局域空心光束.球差系数决定了最佳聚焦点的位置.当球差系数为正时,最佳聚焦点随着球差系数的增大向远离透镜的方向运动,甚至超过几何焦点;当球差系数为负时,最佳聚焦点随着球差系数绝对值的增大向靠近透镜方向移动.另外,在正负球差绝对值相等时,光强分布以几何焦点相对称.     

Nanosecond zero-order pulsed Bessel beam generated from unstable resonator based on an axicon

We present what we believe the first experimental observation of a nanosecond zero order pulsed Bessel beam generated from an unstable resonator based on an axicon. The field distribution at the output coupler is simulated by means of Fox–Li iterative computation. It is shown that the experimental result is consistent with the numerical simulation. The application field and forecast of the zero-order Bessel beams are very wide, such as precision cutting and micro-operation experiment. Our experiments offer a new way to output zero-order Bessel beams directly.     

Effect of vectorial nature on spectral anomalies of ultrashort pulsed beams from a hard-edged aperture

Based on the vectorial Rayleigh–Sommerfeld diffraction integrals, the analytical expression for the spectral intensity of a vectorial nonparaxial ultrashort pulsed Gaussian beam diffracted at a rectangular hard-aperture is derived. The results of the far-field and paraxial cases can be regarded as special cases of the general expression. Effect of vectorial nature on spectral anomalies of ultrashort pulsed beams passing through a hard-edged aperture is analyzed in detail. It is shown that the spectral switch near the phase singularity, which is predicated under the condition of the scalar paraxial theory, disappears with the increasing effect of the vectorial and nonparaxial nature.