球面角锥棱镜非稳腔钕玻璃激光器

为了将虚共焦非稳腔输出光束质量高和角锥棱镜谐振腔具有免调试的优点结合到一起,提出了用球面角锥棱镜构成虚共焦非稳腔的方案。利用已有虚共焦非稳腔钕玻璃激光器,设计加工了一球面角锥棱镜非稳腔钕玻璃激光器。模拟计算了两谐振腔输出光束的模式分布,然后对两钕玻璃激光器进行了实验对比研究。结果表明:实验得到的模式分布与模拟计算结果相吻合,球面角锥棱镜非稳腔钕玻璃激光器与虚共焦非稳腔钕玻璃激光器分别获得了最大2176.9J和2340.6J的能量输出,二者的电光效率与束散基本相同,分别为4.3%,0.30mrad和4.6%,0.26mrad。     

Properties of a laser beam generated from an axicon resonator

A high power cw CO₂ laser beam is generated from a resonator configuration having an axicon mirror as its end reflector. The properties of this beam are evaluated in terms of its polarization, focusing capability and temporal stability and the resulting effects on processing materials are presented. A comparison is made between a folded and a straight resonator having a spherical focusing mirror as its end reflector.     

失调多腔镜型环形谐振腔共轭光轴位置精度分析

为了详细分析由多个反射镜构成的谐振腔内的闭合光轴(共轭光轴)的特性以及存在条件, 首先从光束传输坐标变换的角度, 分析了由多个平面镜所构成的谐振腔的共轭光轴存在条件, 得出了奇数平面镜谐振腔仅当平面镜间具有高精度的相同垂直度时才存在闭合光轴, 而偶数平面镜谐振腔总是存在闭合光轴的结论, 并给出了腔共轭轴随腔镜方向失调而产生的角度变化关系. 然后从矩阵光学的角度分析包含球面镜的谐振腔的共轭光轴在腔镜间传输时的方向变换问题, 具体分析了由两个平面镜和一个球面镜构成的三角形环形谐振腔的闭合共轭光轴存在的问题. 结果表明, 当不同的镜子出现角度偏差时, 腔内仍然存在闭合的共轭光轴, 并给出了对应的腔轴变化以及新谐振面的位置及方向. 由此表明由于球面镜的加入降低了谐振腔共轭轴存在性对平面镜间高精度平行度的要求, 为基于高品质光学无源腔的光谱测量技术的高精度装调工作提供了理论指导.     

Extended application of the complex source-point theory

In this paper, the complex source-point theory used for a symmetric concave spherical resonator is extended to an asymmetric concave spherical resonator. Thus, the formulae for the field distribution of the asymmetric spherical resonator can be easily deduced from the formulae for the field distribution of the symmetric resonator, thereby the application range of the complex source-point theory is enlarged and a convenient method is provided for the field analysis of an arbitrary spherical resonator.     

Performance Investigation of Photonic Crystal-Based Microring Resonator for Optical Signal Processing

Abstract

A detailed theoretical analysis is presented to characterize wave propagation at 1,550 nm inside a glass (SiO₂) microring resonator implemented using photonic crystal technology. A photonic crystal reflection is used at each microring resonator corner to enhance the bending efficiency. The characteristics of both photonic crystal beam splitter and microring resonator bending losses are analyzed and investigated using both effective refractive index and finite difference time domain methods. Analytical expressions are also derived to describe the field enhancement inside the microring resonator, the transfer function of the microring resonator, and the main parameters characterizing the resonator such as resonator band width and quality factor. The analysis is also extended to characterize a drop filter implemented using photonic crystal-based microring resonator. The results indicate clearly that the effective refractive index method can give accurate results if one starts the calculations with finite difference time domain-estimated beam splitter parameters. Further, bending efficiency as high as 99% can be obtained using a ten-post layer photonic crystal mirror at each microring resonator corner.     

Circular modes selection in Yb:YAG laser using an intracavity lens with spherical aberration

The possibility of use of ordinary short-focus lenses with strong spherical aberration for mode selection in a laser resonator is demonstrated. Plano-convex spherical lenses with foci from 2.5 to 10.0 cm placed inside the resonator of the CW laser diode pumped Yb:YAG laser were used to select circular modes of Laguerre-Gauss and Bessel-Gauss type, or to get ring-like, multi-mode off-axis oscillations with variable inner and outer diameters of rings. At the constant pump power mode selection was obtained by shifting an intracavity lens along the resonator axis relative to the Yb:YAG ceramics active element of 1.1 mm thickness. Peaked and hollow multi-ring beams with output power up to 30 mW were produced. Near diffraction free (ndf) propagation of the central part (minimum or maximum) of these beams was observed along distances over 10 m from the resonator output coupler. The mechanisms of mode selection due to spherical aberration in the resonator and ndf propagation of output beams are considered. The possibility of producing radially polarized beams from the laser with an intracavity lens and possible applications of the devised laser scheme are discussed.     

Characteristics of millimeter wave detection in a Fabry-Perot resonator using a YBCO-BiO composite superconductor

A quasioptical technique with a hemispherical-type Fabry-Perot resonator for measuring characteristics of millimeter wave detection using a YBCO-BiO composite superconductor has been successfully developed. This Fabry-Perot resonator consists of a spherical mirror and a plane mirror mounted on the cold head of the refrigerator, under a controlled temperature of 40 to 300 K. The method offers the advantages of estimating irradiation power, easily controlling the sample temperature, analyzing the mode of the irradiated millimeter waves and easily extending to higher frequencies. The superconducting millimeter wave detector has been measured with this technique, with measured sensitivities of 46.5 V/W (70 K) to 160 V/W (35 K) at 50 GHz. These results are close to the theoretical values calculated numerically from the characteristics of the detector. It was confirmed that the millimeter wave detection system using the Fabry-Perot resonator is suitable for estimating the sensitivity of the high-Tc superconducting millimeter wave detector.     

Influence of spherical aberrations on fundamental mode beam quality under different laser resonators

Spherical aberrations of the thermal lens of the active media are severe when solid state lasers are strongly pumped. The fundamental mode profile deteriorates due to the aberrations. Self-consistent modes of a resonator with aberrations are calculated by using the Fox--Li diffraction iterative algorithm. Calculation results show that the aberration induced fundamental mode beam quality deterioration depends greatly on the resonator design. The tolerance of a flat--flat resonator to the aberration coefficient is about 30λ in the middle of stability, where λ is the wavelength of laser beam. But for a dynamically stable resonator, 2λ of spherical aberration will create diffraction loss of more than 40%, if inappropriate design criteria are used. A birefringence compensated laser resonator with two Nd:YAG rods is experimentally studied. The experimental data are in quite good agreement with simulation results.     

Study of the thermal stability of Zerodur glass ceramics suitable for a scanning probe microscope frame

The work presents measurements of the length stability of Zerodur glass ceramic with temperature change. Measurement of this thermal characteristic is necessary for determination of the optimal temperature at which the Zerodur glass ceramic has a coefficient of thermal expansion close to zero. The principle of the measurement is to monitor the length changes using an optical resonator with a cavity mirror spacer made from the Zerodur material to be studied. The resonator is placed inside a vacuum chamber with a temperature control. A tunable laser diode is locked to a certain optical mode of the resonator to monitor the optical frequency of this mode. A beat-note signal from optical mixing between the laser and a stabilized femtosecond frequency comb is detected and processed. The temperature dependence of the glass ceramics was determined and analyzed. The resolution of the length measurement of the experimental set-up is on the order of 0.1 nm.     

High-power CO(2) laser with a Gauss-core resonator for high-speed cutting of thin metal sheets

A novel resonator, the Gauss-core resonator, based on a stable resonator configuration designed to yield a highly focusing beam operating in a large-volume TEM(00) mode, is presented. A 6.2 kW linearly polarized output beam with an M(2) factor of 1.7 is obtained experimentally for a high-power cw CO(2) laser. The capability of the Gauss-core resonator to process laser materials is also studied. We can cut 1-mm-thick mild (soft) steel with a maximum cutting speed of 58 m/min at 5.6 kW and 0.2-mm-thick steel 145 m/min at 2.8 kW.     

CdSSe玻璃在环形腔中的自振荡

两表面镀有高反射膜,自身形成F-P腔的CdSSe玻璃薄片置于环形腔中.在一定的输入光强参数下,反射光信号出现其有某种规律性的振荡.实验观测了作为输入光强函数的不同振荡模式.由于所用样品的光双稳回线宽阔,上下两支有较大的倾斜度,我们观察到较大数目的输出强度上升与下降台阶.简单的绝热模拟表明,自振荡的模式遵从Farey-tree结构.     

Optical microresonator based on hollow sphere with porous wall for chemical sensing

A porous-wall hollow glass microsphere (PW-HGM) was investigated as an optical resonator for chemical vapor sensing. A single mode optical fiber taper was used to interrogate the microresonator. Adsorption of chemical molecules into the nanosized pores induced a refractive index change of the thin wall and thus a shift in its resonance spectrum. The PW-HGM resonator had shown higher vapor detection sensitivity in comparison with a solid microsphere under similar test conditions.     

An "openable," high-strength gradient set for orthopedic MRI.

A novel three-axis gradient set and RF resonator for orthopedic MRI has been designed and constructed. The set is openable and may be wrapped around injured joints. The design methodology used was the minimization of magnetic field spherical harmonics by simulated annealing. Splitting of the longitudinal coil presents the major design challenge to a fully openable gradient set and in order to efficiently design such coils, we have developed a new fast algorithm for determining the magnetic field spherical harmonics generated by an arc of multiturn wire. The algorithm allows a realistic impression of the effect of split longitudinal designs. A prototype set was constructed based on the new designs and tested in a 2-T clinical research system. The set generated 12 mT/m/A with a linear region of 12 cm and a switching time of 100 micros, conforming closely with theoretical predictions. Preliminary images from the set are presented.     

Time-Domain Mapping of Electromagnetic Ray Movement Inside Anisotropic Spherical Resonator

This paper presents the analytical proof of Time-Domain Mapping Method for the spherical resonator made up of uniaxial crystal. In this way, the main types of caustics inside the spherical resonator made up of uniaxial crystal, which were investigated numerically before, are confirmed analytically. It is engraved that the problem of the ray flow inside the spherical resonator can be reduced to the problem of the ray flow inside metal cavity shaped as spheroid.     

跑道形玻璃波导谐振腔滤波器的研制

采用Ag+-Na+离子工艺,在K9玻璃上制备了跑道形波导谐振腔滤波器.测试得到该滤波器自由光谱范围为FSR=0.177 nm,对比对为Cr＝7.5 dB.同时分析得到耦合器的耦合系数为κ=0.916,耦合器和环形腔的损耗因子分别为δ=0.55,γ=0.48.耦合器的两波导几乎相连、条波导边缘不规则和一次离子交换波导表面缺陷是造成该波导滤波器具有较大损耗的主要原因.通过改进工艺技术降低波导损耗,该滤波器可以用于光通信、传感等领域,也可与其它波导结构相结合实现新的功能.     

Special features of the fluorescence of organic molecules with two-photon absorption in a drop upon exposure to a femtosecond laser pulse

A closed system of equations for spherical microresonator modes and populations of energy levels of twophoton excited molecules placed in a resonator and exposed to a femtosecond laser pulse is derived. The threshold of transition of spontaneous emission into stimulated one (in the superfluorescence mode) in a microparticle is established with allowance for the microparticle morphology and laser pulse duration.     

Reflection and transmission of light in medium/cholesteric/substrate and glass (1)/cholesteric/glass (2) systems

Reflection and transmission of light in medium/cholesteric/substrate and glass (1)/cholesteric/glass (2) systems are discussed. These systems can be viewed as a cholesteric-filled Fabry-Perot resonator. A modified layer-addition method is used. Rigorous explicit expressions for the elements of the Jones matrices for these systems are derived. Reflection, transmission, Faraday-rotation, and polarization-ellipticity spectra were studied. The effect of quasi-monochromatism and degree of polarization of light on the refl ection properties was treated in terms of Müller matrices. The influence of the dielectric boundaries on intrinsic cholesteric polarizations was investigated. It is shown that initially quasi-circular intrinsic polarizations turn to quasi-linear as the difference between the cholesteric mean permittivity and the permittivity of the surrounding medium increases. Features of the Borrmann effect in the presence of dielectric boundaries are discussed.     

Quasi Optical Resonator for Measuring Surface Resistance and Its Distribution of High Temperature Superconductor Film

A quasi optical resonator consisting of two spherical mirrors and a new calibration technique were developed to measure the surface resistance Rs and its distribution of high temperature superconductor (HTS) at 94GHz. The Q factor of the open resonator is greater than 1.4×10⁵, and the radius of Guass beam waist is 2.53mm. This method has advantage of being nondestructive, high sensibility, convenient experiment setup.     

连续波锁模掺钕磷酸盐玻璃激光器光学谐振腔的分析

由于Nd:磷酸盐玻璃的热导率和破坏阀值都比较低,故连续波锈模钕磷酸盐玻璃激光器要求其谐振腔有特殊的设计.本文在谐振腔长度固定的限制下,分析了三元件式谐振腔的特性,并且讨论了连续波主动锁模Nd:磷酸盐玻璃激光器光学谐振腔的设计.我们讨论了在不同参量范围下谐振腔的稳定性范围和特性,并且阐明了有关的最佳参数的范围.给出了谐振腔最佳运转区参数的解析表达式.实验结果与理论预测符合得很好.这个解析式对设计三元件或多元件的任何端面泵浦和锁模谐振腔是很有用的.     

Natural oscillations of shielded multilayer spherical dielectric resonators

Characteristic equations and analytic expressions for the Q-factors are derived for a three-layer spherical dielectric resonator in a metal shield. The effect of dielectric coatings on the Q-factors of dielectric resonators is examined. The effect of a metal shield on thinning of the spectrum of a hollow spherical dielectric resonator is investigated.Kiev Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 6/7, pp. 579–586, June–July, 1992.