Theory and design of chirped dielectric laser mirrors

Received: 11 March 1997/Revised version: 26 April 1997     

Novel method for design of surface relief guided-mode resonant gratings at normal incidence

We demonstrate that the surface relief guided-mode resonant gratings with specified central wavelength and FWHM in the visible wavelength range can be designed by analyzing the complex poles of Reflectance and transmission coefficient matrix algorithm (RTCM), a variant of S-matrix propagation algorithm proposed for calculation of multilayer gratings. In addition, FWHM is computed with couple-mode (CM) theory of resonant gratings which is firstly extended by Norton et al. in calculation of waveguide grating. Furthermore, the side band reflections of the filter can be reduced to less than 5% in the visible wavelength with the antireflection (AR) design technique widely used in the thin-film field.     

膜系结构对激光损伤阈值的影响

本文以TiO_2/SiO_2及ZrO_2/SiO_2膜系为例,研究了A(HL)~mHG、A[(2p+1)HL]~m(2p+1)HG以及A[H(2q+1)L]~mHG等不同膜系结构对激光损伤阈值的影响.同时结合光学损耗测量及保护膜厚度效应研究,对光学薄膜的激光损伤机理作了初步探讨.     

Optimal output mirrors for laser resonators

To minimize the angular divergence of a laser output beam, the lens effect of the output mirror must be taken into account. The optimum focal length is given for symmetric and half-symmetric resonators, and the dependence of the minimum beam divergence on cavity parameters is shown.     

Magneto-optical effects in crystals at the normal incidence

We consider the interaction of a polarized electromagnetic wave in a magnetically ordered crystal plate surrounded by an isotropic ambient at the normal incidence. The crystalline medium of the plate is specified by the general non-symmetric permittivity tensor. The results are expressed in terms of the transmission and reflection matrices which relate the electric fields of the incident wave to those of transmitted and reflected waves. Their applications are illustrated by examples of an isotropic plate magnetized normal to the interface, a cubic crystal magnetized parallel to the interface and an orthorhombic crystal magnetized along the axis normal to the interface. The effect of the reflection from the interfaces and the interference effect are included. The paper treats the reflection at an interface between an isotropic ambient and an absorbing magnetic crystal at small non-zero angles of incidence. The general reflection matrix is applied to the determination of the magneto-optical effects quadratic in magnetization.     

Reflection refractometry for nearly normal incidence and at the Brewster angle

We consider and experimentally study two reflection refractometry methods involving reflection of light from the optical surface of a material for nearly normal incidence and for incidence at the Brewster angle. We analyze the sources of error in the methods, and show that it is possible to use laser radiation to measure the refractive index of materials to four decimal places. We note the advantages of the methods in preparing samples for measurements in the case of solid, liquid, film, and weakly absorbing materials.     

Reducing the mirrors coating noise in laser gravitational-wave antennae by means of double mirrors

Recent researches show that the fluctuations of the dielectric mirrors coating thickness can introduce a substantial part of the future laser gravitational-wave antennae total noise budget. These fluctuations are especially large in the high-reflectivity end mirrors of the Fabry–Perot cavities which are being used in the laser gravitational-wave antennae.We show here that the influence of these fluctuations can be substantially decreased by using additional short Fabry–Perot cavities, tuned in antiresonance instead of the end mirrors.     

激光器腔镜夹持方式对热变形的影响

 分析了当前大功率激光器腔镜采用的几种夹持方式特点，采用有限元软件计算了腔镜不同夹持方式下的镜面热变形和镜体最大应力，并对两种夹持方式下的应力破坏进行了分析。发现夹持方式对大功率激光器腔镜镜面变形影响很大，镜体边界沿径向固定的压圈法效果优于沿轴向固定的弹性压板法。     

A new method for increasing the laser damage threshold of metal mirrors

In order to increase the damage threshold of metal mirrors we propose to create a special structure on the surface of the mirrors (“photonic surface”). This structure must have the period about λ/2 and will suppress propagation of surface plasmons with the frequency ω₀=2πc/λ along the surface. This structure will also slightly increase the heat removal from the mirror’s surface by the excitation of the thermostimulated plasmon emission from the surface. The heat removal from the surface is estimated and possible implementation of this approach for use with CO₂-lasers (λ=10.6 μm) and Nd-YAG-lasers (λ=1.06 μm) is analyzed.     

Wave reflection from inhomogeneous media at normal incidence

Wave reflection from a medium with continuously varying refractive index is examined. A differential equation is developed, the solution of which yields the back-reflected part of a wave of unity amplitude incident on a non-homogeneous medium at normal incidence.     

激光器腔镜夹持方式对热变形的影响

分析了当前大功率激光器腔镜采用的几种夹持方式特点,采用有限元软件计算了腔镜不同夹持方式下的镜面热变形和镜体最大应力,并对两种夹持方式下的应力破坏进行了分析。发现夹持方式对大功率激光器腔镜镜面变形影响很大,镜体边界沿径向固定的压圈法效果优于沿轴向固定的弹性压板法。     

Quantum reflection from a solid surface at normal incidence

We observed quantum reflection of ultracold atoms from the attractive potential of a solid surface. Extremely dilute Bose-Einstein condensates of 23Na, with peak density 10(11)-10(12) atoms/cm(3), confined in a weak gravitomagnetic trap were normally incident on a silicon surface. Reflection probabilities of up to 20% were observed for incident velocities of 1-8 mm/s. The velocity dependence agrees qualitatively with the prediction for quantum reflection from the attractive Casimir-Polder potential. Atoms confined in a harmonic trap divided in half by a solid surface exhibited extended lifetime due to quantum reflection from the surface, implying a reflection probability above 50%.     

Numerical modeling of photorefractive crystals for self-adapting external cavity laser mirrors

The process of refractive index grating formation in a photorefractive crystal, used as the self-adapting spectral filter in an external cavity of a semiconductor laser, is studied using a self-consistent model. The model is based on the Finite Difference solution of the Kukhtarev equations. The results obtained are compared with the ones provided by approximate analytical models.     

Operation of a ruby laser with tilted mirrors

The present paper is concerned with a study of the operation of a ruby laser with plane mirrors set at angles of 3–10 relative to each other. It is shown that tilting the mirrors shifts the intensity maximum on the mirrors and deflects the radiation beams toward the further edges of the mirrors. The prevailing patterns in the near and far zones were found to coincide for all mirror tilt directions. The experimental results are compared with theoretical deductions and a conclusion is drawn regarding the modal composition of the radiation.     

Energy distribution of reflected ions at normal incidence on the target surface

Summary The energy distribution of reflected ions at normal incidence of the primary beam on the target surface is obtained as a result of approximate solution of the Boltzmann equation by the method of discrete streams. This method gives the opportunity to avoid the problem of negative distribution function, arising in the generally applied method of spherical harmonics, and to present the final result in analytical form. The analysis is performed for a power scattering cross-section and the theoretical energy distribution demonstrates one maximum when the ion mass is equal to the mass of a target atom, and two maxima when the ion mass is much less than the mass of a target atom.     

A functionally graded structural design of mirrors for reducing their thermal deformations in high-power laser systems by finite element method

In this paper, a new method is proposed to effectively lower the high temperature, smooth the thermal stress and reduce the thermal deformation of mirrors in high-power laser systems utilizing functionally graded materials (FGMs). Two kinds of laser source are discussed at the same time. One is the doughnut-shaped laser, and the other is the Gaussian-distributed laser. Numerical results from finite element analysis show that the thermal deformation of silicon and copper mirrors can be reduced by one order of magnitude, and the temperature rise is also lowered obviously by this means. The effects of slope regulation of the functions for representation of thermophysical and mechanical properties on thermal deformation of mirrors are discussed to meet the requirement of optimum design and manufacture of FGM mirrors for the future.     

An impulse method of measuring normal impedance at oblique incidence

An experimental method of determining the oblique incidence behaviour of sound absorbing materials is given. The method involves the measurement of acoustic impulses at the surface of an absorbing material and comparing the complex frequency components with those of a reference signal recorded remote from the surface. Amplitude and phase characteristics of the reflected signal are thus obtained and hence the normal impedance of the material is found. Comparison between measurements made by the “surface” method and standing wave tube measurements shows good agreement for normal incidence. However, at very oblique angles of incidence the method is in obvious error, the accuracy being limited by a sphericity effect.     

空间遥感器中大口径SiC主镜的轻量化设计

考虑到反射镜质量、尺寸对载荷敏感度、加工困难程度和总成本的影响,阐述了对空间遥感器大口径主镜进行轻量化设计与优化的必要性。叙述了主镜轻量化技术的一般规律,对几种轻量化方式进行了比较并给出了网格筋大小的确定公式。结合具体工程的主镜设计,针对SiC材料的空间反射镜提出了一种背部半封闭、三角形孔的轻量化形式,用迭代方法完成了轻量化设计,并制作了660 mm轻量化SiC反射镜。提出的设计方式解决了单种轻量化方式存在的不足,使单镜满足了质量小、刚度大的要求,为今后大口径SiC主镜的轻量化技术提供了借鉴和参考。