Focusing properties of an off-axis gaussian beam

Focusing properties of an off-axis gaussian beam passing through the optical system with primary spherical aberration are investigated. The position of focus and the structure of the intensity distribution near the focus in the image space are clarified for an off-axis gaussian beam as a function of its incident position over the pupil, its beam size, and the amount of primary spherical aberration in the optical system.     

Variable-diameter refractive beam shaping with freeform optical surfaces

We propose a refractive two-element system that converts the gaussian irradiance of an incident laser beam into a nominally flat-top output spot at a given distance with the capability to vary the spot diameter. The elements are high-order freeform surfaces that, when laterally translated, form a variable composite beam shaper. The general approach for determining the required freeform surfaces is discussed, and example design results are presented.     

Design of a Quasi-Optical System to Convert TE0n Mode Outputs of a Gyrotron into Gaussian Beams

In this paper we present a novel design of a quasi-optical system for conversion of gyrotron outputs into gaussian beams. It consists of a quasi-optical antenna, four focusing mirrors (parabolic cylinders) and a filter which removes the side lobes of the beam. The system is capable to convert three TE_0n mode outputs into gaussian beams with waist size of 16.7 mm as well as four TE_1n mode outputs into bi-gaussian beams with waist size of 10.9 mm in width and 16.5 mm in length.     

Method for converting a Gaussian laser beam into a uniform beam

The use of a phase filter to convert a gaussian laser beam into a beam with more uniform irradiance distribution is discussed. This phase filter is calculated by employing an iterative procedure on a computer. A computer-generated hologram of this phase function is used to experimentally verify the feasibility of this method.     

Gaussian beam parameter transformation at a refracting surface

The Fourier transform method is used to calculate the electric field of the astigmatic gaussian beam which appears when an incident stigmatic gaussian beam is refracted at the interface between media with different refractive indices. A beam parameter transformation law is derived which shows that the beam parameters of the refracted astigmatic beam can be calculated from the beam parameters of the incident stigmatic beam and the angles of incidence and refraction. An heuristic derivation of the transformation law based on geometrical optics is also given. The application of the law is illustrated by determining the plane parallel plate astigmatism.     

Anomalies in the field of a gaussian beam near focus

A theoretical analysis of the electromagnetic field of a focused gaussian beam, like that produced by some lasers, indicates anomalies in the field distribution over the focal region. The transverse component of the electric field is shown graphically in this region using data obtained through the numerical integration of an expression that is exact according to Maxwell's equations. These data agree with the standard paraxial theories used to describe gaussian beams only asymtotically, in the limit of zero beam divergence about focus. As the divergence is increased, so that the beam is brought more sharply to focus, the gaussian beam evolves toward a dipole field from which all evanescent plane waves have been removed. Gaussian beams observed in nature should show some evidence of the associated anomalies, even if the beam is almost collimated.     

Conditioning optics for astigmatic gaussian beams at 140 GHz, 0.5 MW

A quasi optical system was designed to couple the RF power coming from a gyrotron with astigmatic gaussian beam output into a transmission line consisting of an oversized corrugated waveguide. The gyrotron is capable of delivering500 KW at140 GHz for0.5 s. The whole system is described together with low power tests on parts of it.     

二极管面阵侧泵浦Nd:YAG双板条激光器

 叙述了二极管面阵侧泵浦双板条耦合单横模 Q 开关激光器的研制。泵浦源为二极管面阵激光器,使用梯形波导板耦合系统,耦合效率达90%,谐振腔为凸凹腔,全反射镜的曲率半径为 3.0m的凹面镜,输出镜为曲率半径3.0m的可变反射率超高斯镜。激光器在 100Hz 重复频率下,输出单脉冲能量18.23mJ,脉宽为15.25ns,光束质量M²<1.5具有平顶分布的超高斯光束。     

The electromagnetic field of a guided Gaussian beam

An electromagnetic wave traveling along a dielectric slab between two parallel, plane conductors is analyzed for a special case that is particularly relevant to guided laser beams employed in integrated optics. The beam is assumed to have an approximate gaussian field dependence along the y-direction, defined to be transverse to the direction of propagation and to the normal to the conductor planes. Approximate expressions for the field in a well collimated beam are derived. Asymptotic approximations, valid far away from the focus of a beam that is not necessarily well collimated, are also derived. It is found that the TE and TM guided gaussian beams are not linearly polarized. This is unlike the case for the usual waveguide modes whose fields are constant along the y direction. It is also found that the guided gaussian beam must have a focus and that the divergence from focus is more rapid than for a similar gaussian beam in free space.     

Diffraction patterns of off-axis gaussian beams in the presence of third-order spherical aberration in the optical system

The intensity distribution of diffraction patterns for off-axis gaussian beams at the image plane of an optical system with third-order spherical aberration is calculated by using the concept of the beam aberration function previously introduced by the present authors. The results show how the peak intensity of the diffraction patterns diminishes and how the transversel focal shift occurs as a function of the incident position of the beams at the pupil plane and their beam size.     

高斯光束通过非线性介质后的远场衍射图样的研究

 利用菲涅尔－基尔霍夫衍射积分公式，对发散和会聚高斯光束通过薄非线性介质时形成的远场衍射图样进行了研究。模拟计算结果表明：当发散高斯光束通过自散焦介质或会聚高斯光束通过自聚焦介质时，远场均会出现中央较暗、向外围逐渐增强、分布尺度较大的粗衍射环；当发散高斯光束通过自聚焦介质或会聚高斯光束通过自散焦介质时，远场均会出现中心强度最大、向外围逐渐减弱、分布尺度较小的细衍射环。不同远场衍射图样归根结底是入射高斯光束因介质折射率变化造成的空间自相位调制及其波前曲率共同作用的结果。     

Gaussian beam diffraction by a quasi-optical grating for coupling to lower-hybrid plasma waves

This paper is dedicated to the theoretical approach to the problem of modelling quasi-optical launchers of plasma waves in the lower-hybrid range of frequencies, when a gaussian beam is the incident field. Numerical results are presented and discussed comparing the cases of a gaussian beam and a plane wave as an incident field [1].     

Generation of a uniform line source using a binary filter

A uniform or nearly uniform 10 mm long line source has been generated from a gaussian laser beam using a binary filter. This is done by processing the binary filter throughout a well corrected optical system, so that the equivalent of a continuous inverse gaussian filter is obtained at the final image plane. This equivalent continuous filter generates a uniform line source with maximum conversion efficiency of 50%.     

The application of Gaussian beam. Formalism to optical propagation in nonlinear media

The nonlinear propagation problem of optical beams in media with an intensity dependent indices of refraction is solved in the case of a fundamental gaussian beam. This solution is made possible by assuming everywhere along the propagation path a quadratic index profile. The quadratic constant is obtained self-consistently from the second term in a Taylor expansion of the local gaussian intensity. The solution constitutes an extension of the well known ABCD formalism to nonlinear propagation.     

Synthesis of gaussian beam excited rectangular dielectric guide modes by ray theory

In the present paper, ray analysis of the wave propagation has been used to evaluate the excitation of a linear dielectric guide by a gaussian beam. The paper begins by determining the Green's function of the structure and also evaluates the excitation by gaussian beam therefrom, following Falsen and Shin [1].     

Midinfrared dielectric coated metallic waveguides

The transmission characteristics of planar dielectric coated metallic waveguides are investigated. In addition, the coupling of a gaussian beam into the normal modes of these devices and the far field radiated from an open end are discussed in detail.     

遗传算法在激光束整形中的应用

采用遗传算法设计了一个8台阶二元光学元件,可用菲涅耳变换系统将高斯光束变换成均匀圆光束,均匀区能量转换效率达到87％,输出波形比较理想。将遗传算法设计的结果同稳相法和输入输出法设计的结果进行比较,发现在同时降低量化台阶数和增大最细线条宽度的条件下,用遗传算法进行设计并制作出的激光束整形元件仍可以得到满意的变换结果。 关键词：     

The representation of 3D gaussian beams by means of inhomogeneous waves

There are different methods to mathematically represent a bounded beam. Perhaps the most famous method is the classical Fourier method that consists of the superposition of pure homogeneous plane waves all traveling in different directions and having an amplitude that can be found by the Fourier transform of the required profile. This method works perfectly for 2D as well as for 3D bounded beams. However, some researchers prefer the inhomogeneous wave theory to represent a bounded beam because some phenomena, e.g. the Schoch effect, are explained by this method by means of concepts that agree better with intuition. There are several papers dealing with this method for 2D gaussian beams. Until now, it has never been considered possible to represent 3D gaussian beams as well. The present paper shows a method to overcome this shortcoming and presents different sorts of 3D gaussian beams that are built up by means of inhomogeneous plane waves.     

The elliptical gaussian wave transformation due to diffraction by an elliptical hologram

Realized as an interferogram of a spherical and a cylindrical wave, the elliptical hologram is treated as a plane diffracting grating which produces Fresnel diffraction of a simple astigmatic gaussian incident wave. It is shown that if the principal axes of the incident beam coincide with the principal axes of the hologram, the diffracted wave field is composed of three different astigmatic gaussian waves, with their waists situated in parallel but distinct planes. The diffraction pattern, observed on a transverse screen, is the result of the interference of the three diffracted wave components. It consists of three systems of overlapped second-order curves, whose shape depends on the distance of the observation screen from the hologram, as well as on the parameters of the incident wave beam and the hologram. The results are specialized for gratings in the form of circular and linear holograms and for the case of a stigmatic gaussian incident wave, as well as for the normal plane-wave incidence on the three mentioned types of hologram.     

Laser induced thermal profiles in thermally and optically thin films

The temperature field generated by the weak absorption of a gaussian laser beam in an optically and thermally thin film bounded by two transparent plates is discussed. An analytical solution of the problem is presented together with an algorithm for the numerical integration. The influence of the finite thermal conductivity of the plates is shown in an example.