Radially polarized laser beam from a Nd:YAG laser cavity with a c-cut YVO4 crystal

We demonstrate the generation of a radially polarized beam by simply inserting an undoped c-cut YVO₄ crystal into a Nd:YAG laser cavity. In a hemispherical cavity, the cylindrically symmetric, positive birefringence of the YVO₄ crystal extends the stability limit of the cavity length for an extraordinary ray (radial polarization) compared to an ordinary one (azimuthal polarization). By adjusting the cavity length, a radially polarized beam with an output power up to 1 W was selectively obtained. In addition, a higher-order transverse mode was also generated by arranging the cavity design. The method demonstrated in this paper can be readily applied to laser systems with an isotropic laser medium. PACS 42.60.Da; 42.25.Lc; 42.25.Ja     

Production of radially or azimuthally polarized beams in solid-state lasers and the elimination of thermally induced birefringence effects

Production and amplification of radially and azimuthally (tangentially) polarized laser beams are demonstrated. Based on the different focusing between radially and tangentially polarized light in thermally stressed isotropic laser rods, Nd:YAG laser oscillators were developed to produce low-loss stable oscillation in a single polarization. Pure radially polarized light at 70 W with M2 = 2 and on-axis impure radially polarized light at 150 W with M2 = 2.5 were achieved. The radially polarized beams were then amplified while good beam quality and polarization purity were retained. Complete elimination of thermal-birefringence-induced aberrations was demonstrated. This should allow much better beam quality from rod-based high-power lasers.     

Generation of radially polarized Ti:sapphire laser beam using a c-cut crystal

First, it is demonstrated that with a c-cut Ti:sapphire crystal the generation of a nonpolarized laser beam is possible, in contrast to the conventional a-cut Ti:sapphire crystal, which produces a linearly polarized beam. Second, the generation of a radially polarized Ti:sapphire laser beam is demonstrated in combination with a c-cut YVO(4) crystal used as a selector of radial polarization.     

Single higher-order transverse mode operation of a radially polarized Nd:YAG laser using an annularly reflectivity-modulated photonic crystal coupler

We demonstrate single higher-order transverse mode operation of a radially polarized Nd:YAG laser by using a polarization-selective and reflectivity-modulated output coupler. A narrow annular region with low reflectivity fabricated in a photonic crystal mirror behaves so as to select a higher-order transverse mode of a cylindrically symmetric laser beam. A double-ring-shaped radially polarized TM(02) mode beam is stably generated.     

Evanescent Bessel beam generation through filtering highly focused cylindrical vector beams with a defect mode one-dimensional photonic crystal

We propose a simple setup for generating evanescent Bessel beams using the defect mode of one-dimensional (1D) photonic crystal. The angular selectivity provided by the defect mode mimics the role of an axicon for Bessel beam generation. When an azimuthally polarized beam is strongly focused onto a 1D defect mode photonic crystal interface, an evanescent Bessel beam of the first-order is produced, while an evanescent Bessel beam of the zeroth-order will be created under a radially polarized beam illumination. Switching between a donut shape and a solid focal distribution can be easily realized by controlling the polarization of the illumination. Such a versatile evanescent Bessel beam generation may find potential applications in optical trapping.     

Calculation of optical trapping forces on a dielectric sphere in the ray optics regime produced by a radially polarized laser beam

We calculated the optical trapping forces on a microscopic particle in the ray optics regime for the case where a radially polarized laser beam is applied. A higher axial trapping efficiency than for a circularly polarized doughnut beam was predicted due to the large p polarization component. Three-dimensional optical trapping was expected for particles with a larger index of refraction and for objectives with a smaller numerical aperture.     

Simple Nd:YAG laser generates vector and vortex beam

We report a simple Nd:YAG laser that emits radially polarized beam with helical wavefront. The laser cavity consists of a piece of laser crystal and a plane output coupler, and there is no additional polarization component inside it. The pump light is converted into annular profile through de-focal coupling into a multi-mode fiber. For the continuous-wave(CW) operation, the laser emits radially polarized vortex beam, and it is observed that the helical wavefront of the laser beam is switched from right handedness to left handedness when the output coupler is tilted slightly. For the Q-switched operation under the insertion of a Cr4t:YAG saturable absorber inside the cavity, we obtain radially polarized outputs with left-handedness helical wavefront. By tilting the laser crystal slightly, the laser output switches to azimuthal polarization at pump power larger than 4.5 W and left-handedness helical wavefront of laser beam is preserved.     

Electron acceleration to GeV energy by a radially polarized laser

We present a relativistic single particle simulation of vacuum acceleration of an electron by a high-intensity radially polarized laser beam. The inherent complete symmetry of radially polarized laser beam leads to improvement in the trapping and acceleration of an electron so that an electron can be accelerated to the level of GeV. In addition, the external magnetic field further enhances the electron acceleration. Hence, an electron of ultrahigh energy was observed. The strong correlation between final electron energy and scattering angle is discussed.     

Study on Optimum Incident Angles of Cross Polarized Four-Wave Mixing with a Photorefractive Crystal

We consider the optimum incident angles of cross polarized four-wave mixing with a photorefractive crystal. First, the phase matching angles are obtained for two operation modes: one in which the writing beams are ordinary rays and the reading beam is an extraordinary ray, we call this Mode 1. The other in which the writing beams are extraordinary rays and the reading beam is an ordinary ray, Mode 2. Next, practicable ranges of the incident angles are calculated considering of the total internal reflection of the phase conjugate beam in cases where the two writing beams illuminate the same surface of the BaTiO₃ crystal and where they illuminate the neighboring right-angled surfaces, respectively. Then, the coupling coefficient is determined as a function of the incident angle, and the optimum incident angles for effective beam interaction in Mode 1 and Mode 2 are estimated.     

Simultaneous generation of helical beams with linear and radial polarization by use of a segmented half-wave plate

Simultaneous generation of helical beams with linear and radial polarization is demonstrated by use of a segmented half-wave plate in a Ti:sapphire laser cavity. A linearly polarized Laguerre-Gaussian beam is converted to a radially polarized beam with a spiral phase shift and vice versa. In addition, these two beams coexist in the cavity, and the cavity emits one of these two beams from an output coupler.     

非均匀关联径向偏振部分相干光的产生

从理论和实验两方面对非均匀关联径向偏振部分相干光的产生进行了研究.理论上,基于相位关联与相干度的联系,推导出了非均匀关联径向偏振部分相干光的2×2阶交叉谱密度矩阵及相干度分布.实验上,利用一个相位型液晶空间光调制器的不同区域,对入射的完全相干的径向偏振光的两个正交偏振分量分别加载随机相位调制,并实验测量了这种光束的相干度分布及其对光强分布的影响.实验结果验证了光束相干度的非均匀关联结构,并且通过改变随机相位的高斯调制半宽可以改变光束的相干性分布.研究表明,随着随机相位的高斯调制半宽的增加,光束中两点间的相干度逐渐减小,其光强分布由圆环状逐渐变化为类平顶的光强分布.这种非均匀关联的径向偏振部分相干光在激光微操纵和材料加工等领域具有一定的潜在应用价值.     

光扇效应对Ce∶KNSBN记录偏振组态的影响

在非同时读出条件下,采用Ar+ 514.5 nm单色激光为光源。以信号光为非寻常偏振光(e光),通过改变抽运光的偏振态,研究不同写入光偏振组态下Ce∶KNSBN晶体的两波耦合特性。结果表明     

Generation of a radially polarized laser beam by use of a conical Brewster prism

To generate a radially polarized laser beam we designed and fabricated a new Brewster optical element that consists of convex and concave conical prisms. The lateral surface of the convex conical prism was coated with a dielectric multilayer (SiO2 and Ta2O5) to enhance polarization selectivity. By combining two prisms we obtained a conical Brewster prism without beam divergence owing to refraction. A radially polarized TEM01* (R-TEM01*) mode laser beam was demonstrated when this prism was used inside a Nd:YAG laser cavity.     

Polarization manipulated solid-state lasers with crystalline-orientations

The polarization states of 〈111〉-cut Yb:YAG crystal microchip lasers were investigated by pumped with the elliptically polarized pump beam from fiber-coupled laser-diode. The manipulated polarized lasers were achieved in laser-diode pumped Yb:YAG microchip laser by controlling the crystalline-orientations in 〈111〉-growth Yb:YAG crystal. Generally elliptically polarized lasers were obtained in laser-diode pumped Yb:YAG microchip lasers. However, crystalline-orientation manipulated linearly polarized laser was obtained when six different sites with different crystalline orientations were set to parallel to the major axis direction of the elliptically polarized pump beam. Six different sites in Yb:YAG crystal were separated with 30° and 90°, which were responsible for the linearly polarized laser oscillations. Circularly polarized lasers were observed when a Yb:YAG crystal was aligned to a special position between two sites responsible for linearly polarized laser oscillation. Effects of the polarization states of pump source on the laser polarization states of Yb:YAG microchip lasers and polarization direction of different polarized lasers with respect to Yb:YAG crystal rotation was addressed.     

基于内腔布儒斯特双轴锥棱镜的掺镱光纤激光器的径向偏振模振荡

实验采用一个内腔布儒斯特双轴锥棱镜,在掺镱多模双包层光纤激光器中实现了径向偏振光振荡,并在长2 m的增益光纤中获得了高达6.2 mW的功率输出.研究揭示了从光纤激光器振荡中获得径向偏振光的新途径.然而,该激光器输出的径向偏振光的光强分布并不很均匀,且偏振消光比较低,需要进一步改进.     

Generation of radially polarized mode in Yb fiber laser by using a dual conical prism

For the first time to our knowledge, a radially polarized beam is generated in an Yb-doped multimode double-clad fiber laser by using an intracavity dual conical prism. Up to 6.2 mW of output power is obtained from a 2 m long gain fiber with 7.4% slope efficiency. This research opens a new window to obtaining a radially polarized beam directly from an active fiber.     

Mutually pumped phase conjugate mirror using cross polarized photorefractive coupling

This paper presents a new proposal for a mutually pumped phase conjugate mirror (MPPCM) using cross polarization. In the cross polarized MPPCM, two light beams, whose polarizations are orthogonal to each other, incident on a photorefractive crystal, causing photorefractive interaction to generate phase conjugate waves with an orthogonal polarization to an incident beam. The use of Ar⁺ laser and BaTiO₃ crystal in an experiment for the cross polarized MPPCM found that diffraction efficiency for an extraordinary beam is about 20%. As opposed to a conventional parallel polarized MPPCM in which the use of a beam splitter is required to separate a diffraction beam, the cross polarized MPPCM can efficiently extract phase conjugate waves by means of a polarized beam splitter, demonstrating the advantage of substantially improved efficiency.     

一种高精度光学位移传感器的设计分析

利用晶体双折射和由散射偏振引起的光学干涉技术,设计出一种高精度光学位移传感器.该传感器采用同轴光学系统,测量精度约为4 μm,测量范围不小于28 mm,且测量时不需要使用相干光源,故结构紧凑、性能稳定.     

Radially polarized 3 kW beam from a CO2 laser with an intracavity resonant grating mirror

A 3 kW radially polarized beam is generated from a CO(2) laser by means of a resonant grating mirror. The design results and spectral characterization of a broadband polarizing mirror are presented as well as the mirror's operation in a CO(2) laser resonator. In a long-term experiment a radially polarized beam with a power of 2.7 kW was observed for several hours, proving the high stability of this polarizing scheme.