充液型可调焦液态透镜

可调焦液态透镜因具备体积小、成像好、调焦方便等优点而备受瞩目.使用透明的弹性薄膜和光学平板玻璃将一定体积的液体封装在圆柱形的空腔内,当空腔内的液体体积变化时,透镜的曲率半径随之而改变,实现了透镜的可调焦.实验表明,该可调焦液态透镜有较好的成像效果,在一定液体体积变化范围内符合薄透镜成像的规律,在通讯、国防、医疗等方面具...     

Design of liquid-glass achromatic zoom lens

Optical liquids are ideal materials for designing apochromatic lens due to their lower refractive index and higher Abbe numbers than those of the ordinary optical glasses. Based on the Buchdahl dispersion formula, the dispersion coefficient diagram of liquids and glasses is established. The liquid-glass combination lens(LGCL) with small secondary spectrum is obtained by calculating the combination structure with low dispersion liquid and glasses. The initial optical structure of the liquid-glass apochromatic lens(LGAL) can be obtained by replacing two glass lenses in an initial optical system with the LGCL. Using the multi-configuration optimization of ZEMAX, the liquid-glass achromatic zoom lens (LGAZL) can be designed by optimizing the LGAL. The LGAZL has an objective field of view ?63 mm–?57 mm, an image field of view 8 mm, a working distance 240 mm and the zoom range of focal length 75–85 mm. The chromatic aberration and the secondary spectrum of the LGAZL are all less than 3 μm in the whole zoom range.     

Focal length measurement of a varifocal liquid lens with capacitance detection

This paper reports on a detailed deformation model of varifocal liquid lenses fabricated by Parylene-on-liquid-deposition (POLD), which can be applied to measure and adjust the focal length of such lenses without using extra sensors or sensing mechanisms. The lens was fabricated by encapsulating a liquid between a transparent electrode and a polymer film that was covered with a metal electrode. When voltage is applied to the two electrodes, the lens deforms due to the electrostatic force, and its focal length and the capacitance between the two electrodes change simultaneously. This characteristic enables the focal length of the lens to be adjusted and detected by measuring the capacitance change. The focal length of the fabricated varifocal liquid lens changed from 153.6 to 82.6 mm by applying 150-V. The focal length change of the liquid lens was calculated from the change in its capacitance. Finally, to confirm the efficiency of this varifocal liquid lens, we fabricated a confocal distance sensor using the lens for laser scanning and demonstrated that this system can be used to measure distances of 94–140 mm with an average error of 0.83 mm and a standard deviation of 0.77 mm.     

宽光谱长焦距物镜的复消色差设计

介绍了以摄远型为初始结构的宽光谱长焦距折射式物镜的设计方法。对玻璃材料的选择进行了分析,并建立了能够分配三分离透镜组光焦度的复消色差方程组。通过理论计算和ZEMAX光学设计软件的优化,给出工作波长范围在0.4~0.9μm、焦距为400 mm、视场角为6.2°、相对孔径为1∶4的设计实例。设计结果表明,二级光谱得到了很好的校正,像质优良。     

Design and fabrication of fluid controlled dynamic optical lens system

A novel small fluid controlled optical lens system that is capable of displaying dynamic variation of its focal length and field-of-view (FOV) is designed and fabricated. In this active lens system, appropriate volume of the optical fluid can be pumped into or out of the lens chamber to provide double-convex (DCX) or double-concave (DCV) lens effect. Simple optical imaging experiments were performed using different sets of glass lenses with fixed focal lengths to determine the optimum lens configuration required for designing a dynamic optical lens system. The experimental results obtained from the glass lenses demonstrate that a combination of a single DCX lens with three DCV lenses provides a wider FOV. The flexible membranes for fluid controlled lenses were fabricated using polydimethylsiloxane polymer material, which has good optical transparency and elasticity. A simple fluid injection system is used to vary the radius of curvature of the lenses, and thereby to change the focal length. A dynamic optical lens system with a combination of one DCX and multiple variable focal length DCV lenses as designed here can image an object with a wide range of focal length and FOV. With this fluid controlled optical system, the FOV and focal length could be continuously varied and a maximum FOV of 118.3° could be achieved. The smallest f-number (f_/#) for this fluid controlled single lens system was found to be 1.3, which corresponds to the numerical aperture value of 0.35.     

多重结构的体全息存储傅里叶变换光学系统设计

分析了体全息存储傅里叶变换光学系统的设计要求和光学参量的确定。采用多重结构方法对傅里叶变换镜头的正向和逆向光路同时进行了优化,可实现对两对物像共扼位置控制像差。给出了前后组焦距分别为44mm和40mm的达到衍射受限要求的4片型球面全息存储光学系统的设计结果。     

等离子体削波纳秒激光脉冲波形测量

实验上采用比对方法测试了激光不经过固体与经过固体介质产生等离子体削波的脉冲波形信号,获得等离子体削波效应产生的脉冲削波倍数。实验结果表明,在波长1.064 m,脉宽1 ns,聚焦透镜焦距100 mm,薄石英片厚度100 m,约束等离子体的小孔直径80 m情况下,等离子体效应产生的脉冲削波倍数为12~14;分别改变石英片厚度和约束等离子体小孔直径,等离子体脉冲削波倍数不变;增加入射激光能量,脉冲削波倍数增加,且经过等离子体后的激光脉冲波形的后沿逐渐出现很陡的下降沿。在产生脉冲削波的截断点位置进行图形拼接重构得到激光脉冲波形信息。     

Nondestructive 3-D imaging of femtosecond laser written volumetric structures using optical coherence microscopy

Nondestructive three-dimensional imaging of femtosecond laser-written buried structures is demonstrated using optical coherence microscopy providing lateral and depth resolution on a micron scale. This high speed technique, which requires no sample preparation, enables the visualization of volumetric structural modification created deep in transparent dielectric medium with high signal/noise contrast. Images of buried void structures with dimensions as large as 190 μm in length were obtained without shadowing effects impugning the image fidelity.     

An efficient directional coupling from dielectric waveguide to hybrid long-range plasmonic waveguide on a silicon platform

The silicon-based three-dimensional hybrid long-range plasmonic waveguide not only supports long-range propagation distance (~mm) but also has an ultra-small modal area (~10^?2 μm²) at 1.55 μm. Here, we propose a directional coupler for effective coupling from a dielectric slab-waveguide to the hybrid plasmonic waveguide on a silicon platform. Our simulation results show that the coupler is able to excite hybrid long-range plasmonic mode with short coupling length, low insertion loss, and high extinction ratio. With the arm separation of 0.3 μm, the coupling length can be made 5.2 % of the propagation length of the hybrid plasmonic waveguide, while the insertion loss and extinction ratio are ?0.12 and 22.4 dB, respectively. This coupler offers the potential applications in signal routing between the hybrid long-range plasmonic waveguide and dielectric waveguide in the photonic integrated circuits.     

Detection of laser induced dielectric breakdown in water using a laser doppler vibrometer

This study is focused on exploring the feasibility of an all-optic surface scanning method in determining the size and position of a submerged, laser generated, optoacoustic (OA) source. The optoacoustic effect in this case was generated when the absorption of a short electromagnetic pulse in matter caused a dielectric breakdown, a plasma emission flash and a subsequent acoustic wave. In the experiment, a laser pulse with λ = 1064 nm and 12 ns pulse length was aimed at a volume of deionized water. When the laser beam was focused by a f = 16 mm lens, a single dielectric breakdown spot occurred. When a f = 40 mm was used several breakdowns in a row were induced. The breakdowns were photographed using a double shutter camera. The acoustic wave generated by the dielectric breakdowns were detected at a point on the water surface using a laser Doppler vibrometer (LDV). First, the LDV signal was used to calculate the speed of sound with an accuracy of 10 m/s. Secondly, the location and length of the dielectric breakdown was calculated with an accuracy of 1 mm. The calculated position matched the breakdown location recorded by a camera. The results show that it is possible to use LDV surface measurements from a single spot to determine both the position and length of the OA source as well as the speed of sound in the medium. Furthermore, the LDV measurements also show a secondary peak that originates from the OA source. To unravel the origin and properties of this interesting feature, further investigations are necessary     

Efficient design considerations for end-pumped solid-state-lasers

The temperature distribution in the gain medium and key design parameters for an ideal-four level end-pumped solid-state laser have been analyzed depending on the crystal's length, absorption coefficient, and pump beam M² factor. The optimum key design parameters and thermal focal lens are obtained by minimizing the root mean square of pump beam radius in the laser crystal. It is found that the focal thermal lens and key design parameters are dependent on the gain medium characteristics and pump beam properties as well. By considering the Poisson equation in cylindrical coordinate and Top-Hat pumping profile, an analytical formula has been derived to introduce the thermal focal length in the end-pumped lasers. A formula is also presented to relate the requirements of pump source to the gain medium properties for working laser at the design point.     

Design and fabrication of long focal length microlens arrays

In this paper, we present microlens arrays (MLA) with long focal length (in millimeter range) based on thermal reflow process. The focal length of microlens is usually in the same order of lens diameter or several hundred microns. To extend focal length, we made a photoresist (SU-8) MLA covered by a Polydimethylsiloxane (PDMS) film on a glass substrate. Because the refractive index difference between PDMS and photoresist interface is lower than that of air and MLA interface, light is less bended when passing through MLA and is focused at longer distance. Microlenses of diameters from 50 μm to 240 μm were successfully fabricated. The longest focal length was 2.1 mm from the microlens of 240 μm diameter. The numerical aperture (NA) was reduced 0.06, which is much lower than the smallest NA (~ 0.15) by regular thermal reflow processes. Cured PDMS has high transmittance and becomes parts of MLA without too much optical power loss. Besides, other focal lengths can be realized by modifying the refractive index different between two adjacent materials as described in this paper.     

Mathematical simulation of the femtosecond-laser inscription of optical waveguides

Based on the hierarchy of mathematical models with regard to parallel algorithms and effective systems, the interaction of a femtosecond-laser pulse with a transparent dielectric medium (fiber-optic glass) is numerically simulated. The features of this interaction are studied for the initial Gaussian and ring distributions of the laser beam. The critical powers at which a local collapse of the beam takes place are determined for the Schrödinger equation. A comparison of the results obtained using various models is presented.     

Laser opto-acoustic study of phase transitions in metals confined by transparent dielectric

First-order phase transitions in metal induced by nanosecond laser pulse are studied here. The metal surface is irradiated through a layer of transparent dielectric??an optical glass. Such confinement considerably increases the efficiency of pressure generation at the metal surface. This technique allows to obtain near-critical states of metals??with temperatures ??10⁴ K and pressures ??10⁴ atm with table-top equipment. At the same time the glass prevents the ablation plume formation??so the surface temperature can be measured using thermal radiation data. An experimental setup for simultaneous measurements of pressure, temperature and reflectivity was assembled based on the elaborated method of experimental research. The processes of melting of lead and boiling of mercury were studied. The onset of the phase transition process led to a considerable tightening of the pressure pulse. A substantial drop of surface reflectivity due to increase of temperature and decrease of density was observed.     

Effects of an absorptive coating on the dynamics of underwater laser-induced shock process

The effects of an absorptive coating on the dynamics of underwater laser-induced shock process have been observed from the end of laser pulse to hundreds of microseconds after irradiation by time-resolved imaging techniques. A laser pulse of 13 ns at 1,064 nm was focused by a 40-mm focal length lens onto the surface of epoxy-resin blocks immersed in water to induce the shock process in the confining regime. A custom-designed time-resolved photoelasticity imaging technique and a high-speed laser stroboscopic videography technique in photoelasticity mode were used to analyze the evolution of shock waves in the water phase, the strength of stress waves in the solid phase, the oscillation of cavitation bubbles, and the generation of bubble-collapse-induced shock waves. We showed that black paint coating enhances the strength of laser-induced stress wave inside the solid, drives faster shock waves traveling in the water phase, and produces higher-energy cavitation bubbles. We propose that even at power densities of 1 GW/cm² and above, an absorptive coating can intensify the shock process by enhancing the absorption of laser energy by plasma.     

Single-focusing regime of propagation of femtosecond light packets when self-focused in a condensed medium

Numerical simulations are used to investigate the propagation of tightly focused megawatt femtosecond light packets in a nonlinear condensed medium in the single-focusing regime. A plasma is shown to be generated in a small region whose length and diameter increase with power in the single-focusing regime of propagation of a femtosecond light packet in a transparent dielectric. The limiting electron density in the microplasma formation region is virtually independent of the laser pulse power but increases with numerical aperture of the focusing optics. At a fixed femtosecond pulse power exceeding the critical self-focusing power, the transmission of light by a dielectric layer decreases with increasing numerical aperture of the focusing optics.     

Bulk Nd3+-doped tellurite glass laser at 1.37 μm

We have demonstrated, for the first time to our knowledge, lasing at 1.37 μm in a tellurite-based glass host doped with 0.5 mol.% neodymium: Nd³⁺:(0.8)TeO₂–(0.2)WO₃. The gain-switched laser could be operated with 59 μJ threshold pulse energy as well as 5.5% slope efficiency. As high as 6 μJ-pulses with a duration of 1.74 μs were obtained. The pulse repetition rate was 1 kHz. The emission cross section from the threshold analysis turned out to be 1.57×10^?20 cm² at 1370 nm by taking into account excited-state absorption from ⁴F_3/2 to ⁴G_7/2 energy level. Furthermore, the ratio of excited-state absorption to the emission cross section was found out to be 0.78 by using the slope efficiency value.     

纳秒脉冲表面介质阻挡放电特性实验研究

在常规大气环境条件下,基于单极性纳秒脉冲电源对表面介质阻挡放电特性进行了实验研究。结果表明:纳秒脉冲表面介质阻挡放电的本质是丝状放电,放电集中在电压脉冲的上升沿;激励电压和脉冲重复频率越大,放电越强烈,越接近均匀放电,但电压的作用更侧重于均匀性,而频率的作用则侧重于放电的强度;电极间隙的优化可以使表面介质阻挡放电特性最好;玻璃作为阻挡介质时容易发生沿面闪络。     

熔石英相位共轭镜无损工作状态分析

基于非线性光学耦合波方程组建立了聚焦泵浦条件下熔石英玻璃材料中SBS过程的物理模型并编制了相应的数值求解程序,研究了SBS介质内激光场的时空发展特征,从而试图揭示SBS介质的内在破坏机制并寻求相应的加固措施.通过数值模拟程序研究了焦点处激光功率密度以及SBS反射率与激光能量的依赖关系,发现SBS对介质内的激光场具有"限幅"作用,即在注入能量大幅度提升的情况下,内部的激光场强度只有较小的增加,这种机制使大能量的固体介质PCM成为可能.分析激光脉宽以及耦合透镜焦距等参数对SBS过程的影响发现,精细选择系统参数,在熔石英玻璃材料中有可能无损伤地实现高效的SBS过程.