Position dependence of growth rate in convection enhanced laser CVD of carbon rods

The ability to closely monitor LCVD rod growth in the growth region is demonstrated in the context of the first open-air axial convection enhanced micro-reactor. It was used to monitor carbon rod growth inside coaxial cylindrical flows of ethylene and argon. Monitoring and subsequent image analysis of the 656 nm atomic hydrogen emission from ethylene pyrolysis allowed real-time in-situ determination of axial growth rate and diameter along the axis of the produced carbon rods for the first time. Growth rates appear to vary greatly inside the growth region. This experiment raises questions about published qualitative models of LCVD rod growth that favor a uniform steady state regime. If the trend demonstrated in our experiments is not just an artifact of flow mixing, then it would indicate that published registered growth rates may just be an average value or an artifact of focus tracking. The results, therefore, point the way to experiments that would allow discrimination between the effect of flow mixing and the true nature of LCVD rod growth in the growth region. PACS 81.16.Mk; 81.10.Bk; 81.05.Uw     

A study of the Soret effect in laser-induced chemical vapor deposition

This paper presents an investigation of the modeling of the process of pyrolytic laser-induced chemical vapor deposition (LCVD) applied to study the Soret effect. LCVD is a thermally activated process characterized by strongly coupled mass and energy transport phenomena, together with chemical reactions, which are difficult to investigate experimentally. A physical and numerical model based on a commercial computational fluid dynamics package is developed and used to simulate a reactor operating at conditions of room temperature and pressure. The proposed numerical methodology will allow us to assess and analyze the effect of various factors controlling the process, and in particular the Soret effect. This numerical model is validated by comparison with the measured growth rate of the fiber. While several studies have proposed simulations of the LCVD process, this is among the first attempts at including the Soret effect in the numerical modeling at the micro-scale level. It is expected that the fundamental insights thus obtained will guide experimental investigations which can be applied to establish reactor design and process control guidelines.     

Gas phase versus surface contributions to photolytic laser chemical vapor deposition rates

The rate of cwphotolytic laser chemical vapor deposition (LCVD) of platinum is measured for 350 nm as a function of the light intensity and the metalorganic vapor pressure. The growth of the metal films is studied in situ and in real time by monitoring their optical transmission. At low intensities the transmitted light decreases monotonically with time, and the LCVD process is photolytic with its rate limiting step in the surface adlayer. At higher intensities we observe two distinct time domains: Relatively slow initial photolytic deposition with its rate limiting step in the gas phase, which is followed by much faster pyrolytic LCVD. An improved method for distinguishing between adlayer and gas-phase limiting processes is demonstrated. These observations are confirmed by studying the photolytic deposition rates while varying the thickness of the adlayer.     

Temperature effects in the photolytic LCVD of platinum

The photolytic laser chemical vapor deposition (LCVD) rate of platinum from its bishexafluoroacetylacetonate precurser has been measured in situ and in real time. Optical transmission of the 350 nm photolysis light through the deposited platinum film and a transparent glass substrate is monitored and analysed in detail. From these measurements, as well as measurements of the reflected light, the fraction of the laser beam power absorbed in the metal film is found. The latter allows a simple estimate of the laser-induced temperature rise at the metal surface. It is shown that even rather small temperature increases of the order of several tens of degrees centigrade can completely change the photolysis mechanism and hence drastically influence the photolytic LCVD rate. A simple modification of Lax's model, in which a temperature dependent thermal conductivity of the substrate is introduced, is used to describe the laser-induced heating of a strongly absorbing thin metal film on a glass substrate.     

Effects of excimer laser illumination on microdrilling into an oblique polymer surface

In this work, we present the experimental results of micromachining into polymethy-methacrylate exposed to oblique KrF excimer laser beams. The results of low-aspect-ratio ablations show that the ablation rate decreases monotonously with the increase of incident angle for various fluences. The ablation rate of high-aspect-ratio drilling with opening center on the focal plane is almost independent of incident angles and is less than that of low-aspect-ratio ablation. The results of high-aspect-ratio ablations show that the openings of the holes at a distance from the focal plane are enlarged and their edges are blurred. Besides, the depth of a hole in the samples oblique to the laser beam at a distance from the focal plane decreases with the increase of the distance from the focal plane. The number of deep holes generated by oblique laser beams through a matrix of apertures decreases with the increase of incident angle. Those phenomena reveal the influence of the local light intensity on microdrilling into an oblique surface.     

一种新型透射式自聚焦光栅的设计及理论研究

结合普通透射光栅的分光特性和菲涅耳波带片的聚焦特性,提出一种应用于软X射线波段的新型透射式自聚焦光栅。根据菲涅耳衍射理论,对其衍射特性进行理论推导,证明该新型光栅存在一个与光栅平面垂直的焦平面,不同波长的光波聚焦于该焦平面的不同位置。在焦平面上,焦点位置随光子能量的变化是线性的,即能实现光子能量的线性测量。通过解析推导,得到在沿着焦平面和垂直于焦平面两个方向上光斑的展宽模式,发现该新型光栅在沿着焦平面的光斑展宽模式不同于普通光栅。根据基尔霍夫衍射公式,设置实用化参数,对其衍射模式进行了详细的数值模拟研究,并讨论了相应的测谱范围和谱分辨率。     

一种新型透射式自聚焦光栅的设计及理论研究

结合普通透射光栅的分光特性和菲涅耳波带片的聚焦特性,提出一种应用于软X射线波段的新型透射式自聚焦光栅。根据菲涅耳衍射理论,对其衍射特性进行理论推导,证明该新型光栅存在一个与光栅平面垂直的焦平面,不同波长的光波聚焦于该焦平面的不同位置。在焦平面上,焦点位置随光子能量的变化是线性的,即能实现光子能量的线性测量。通过解析推导,得到在沿着焦平面和垂直于焦平面两个方向上光斑的展宽模式,发现该新型光栅在沿着焦平面的光斑展宽模式不同于普通光栅。根据基尔霍夫衍射公式,设置实用化参数,对其衍射模式进行了详细的数值模拟研究,并讨论了相应的测谱范围和谱分辨率。     

Computational modeling of forced flow laser chemical vapor deposition

Laser chemical vapor deposition (LCVD) utilizes a laser to localize a CVD reaction. The process involves complex physical interactions within a very small spatial region. Experimental investigations into the dynamics of the LCVD process are limited by spatial and resolution capabilities of instrumentation. Models are developed herein using the computational fluid dynamics (CFD) code, FLUENT, that incorporate heat transfer, fluid flow, and species transport in a single integrated modeling environment. The models are used to study the carbon deposition process. Insight is gained into the relationships among the process parameters and the deposition rates and deposition rate profiles. Phenomena such as thermal diffusion and the relative importance of mass convection and mass diffusion are explored. A designed set of model cases is executed and the results are used to develop a simple polynomial expression for relating experiment conditions to deposit attributes. PACS 81.10.Bk; 81.05.Uw; 81.15.Gh; 47.50.Cd; 81.16.Mk     

TFA-MOD法制备YBCO薄膜生长速率研究

采用原位电阻法对TFA-MOD法高温热处理阶段YBCO薄膜生长速率进行了研究。实验结果和分析表明原位电阻测量法是一种估算YBCO层生长速率的有效方法,不同条件下的测量结果表明薄膜生长速率随管式炉内的温度、水分压、气体流量的上升而明显增加,但随薄膜面积的增加而减小。实验结果为进一步探索和优化热处理过程提供了重要的基础。     

Diffractive optical element used to control side lobe to be extremely low in a large region

In this paper, a diffractive optical element (DOE) is adopted to control the side lobe to be extremely low in a large region on the focal plane, and simultaneously the intensity of the center point on the focal plane is required to be maximal. The DOE to realize the before-mentioned performance is two-phase distributed, i.e. 0 and π. Linear programming is applied to design the DOEs to realize an extremely low side lobe in different regions on the focal plane. Simulated results show that the more rigorous the side lobe is controlled to be, the smaller the intensity of the center point on the focal plane.     

Design of Fresnel lenses and binary-staircase kinoforms of low value of the aperture number

The design of plane Fresnel zone plates, and binary-staircase kinoforms, has been analyzed in this paper for a non-imaging application aimed to increase the performance of point-like detectors. They maximize the irradiance at the focal point of the diffractive element maintaining some constrains in the lateral size of the element. The design of the binary-staircase kinoform has been described as an iterative process. Some interesting results have been obtained for the values of the relative aperture number, or F/#. The practical case treated here produces elements with very low F/#. The results shows that the gain of the irradiance at the focal point increases with the focal distance of the binary-staircase kinoform, and decreases with the focal length for a plane Fresnel zone plate having a limited lateral size. The calculation of the width of the irradiance distribution makes it possible to select those solutions that best concentrate the irradiance on the focal plane.     

Experimental study of the noise emission of personal computer cooling fans

A controlled experimental study of the noise emission of a typical model of computer cooling fan, under different operating conditions, was done. The sound-power levels and directivities of 80-mm-diameter Panaflo computer fans mounted in a test plenum were determined from measurements of sound-pressure level over a hemi-spherical surface above a reflecting plane. The design and testing of the test plenum is discussed. Results of tests performed on one fan unit to gain an understanding of the fan’s noise-radiation characteristics and how they vary with operating conditions are presented. The results show that the noise emission of the Panaflo fan is directly related to the voltage and inversely related to the air-flow rate. It was found that the noise level measured at one particular position corresponds well to the average of those measured at 10 points on the hemisphere. The variability of the noise radiation from these Panaflo fans was determined by testing three other fans; variations of resulting total A-weighted power levels were within 1 dB.     

光斑偏移对空间激光通信系统性能的影响

为了评估大气湍流、通信平台振动和校装误差等因素引起的光斑偏移现象对空间激光通信系统通信性能的影响,理论计算和实验测量了空间激光通信系统中APD光电转换后的电信号幅值随会聚信号光斑和光电探测器光敏面之间的横向位移、以及探测平面和透镜焦平面之间的离焦量的变化关系,同时给出了系统误码率、信噪比、抖动与相偏移量之间的实测曲线。结果表明,空间激光通信系统性能随横向位移以及离焦量的增加而急剧恶化,且横向位移的影响远大于前后离焦的影响。在实验参数条件下,当系统误码率从10-10变化到10-5时,允许系统横向位移和离焦量分别为0.03和1 mm。     

Electromagnetic effects for the resonance-domain IR diffractive optics

Binary optics technology enables the manufacture of arrays of diffractive micro-optical elements which are used in many optoelectronic devices, e.g. the focal plane collection optics. The first-order diffraction grating efficiency decreases in the best part of the resonance-domain region of diffraction, i.e. when the grating period is close to the optical wavelength in the substrate material. A large fraction of the fast binary lens surface relief is built of staircase annular structures whose width is of wavelength scale. Therefore, the rigorous electromagnetic theory of gratings has been applied in this paper to calculate and analyze the diffraction effects for the resonance-domain longwave (8–12 μm) infrared (LWIR) binary optics. It is shown that electromagnetic effects limit the speed of the LWIR first-order diffractive lenses and the optical gain achievable with the diffractive lenses used as the focal plane collection optics in the IR detection systems.     

星载离轴多光谱相机焦平面的装调与检测

针对某离轴多光谱相机焦平面高精度的装调要求,设计了焦平面组件,阐述了装调、检测的仪器设备和方法。首先将焦平面组件安装至镜头,测量并解算出CCD光敏面的角度和位移偏差,接着根据偏差确定调整垫修研量,进行初次修垫并重新安装,然后利用调整工装微调CCD姿态至满足指标要求,调整垫处打销钉定位,最后根据拟合出的最佳焦平面位置再次修研调整垫,利用销钉复位完成装调工作。检测结果表明,相机的CCD光敏面相对于设计焦平面三维角度偏差分别为Δα=-6.7″,Δβ=1.9',Δγ=13.2″,三维位移偏差分别为Δx=-0.004 mm,Δy=0.006 mm,Δz=-0.070 mm,相机四谱段、全视场MTF优于0.25,满足设计和装调要求。测量和解算误差分析表明,所用的设备与方法能够满足装调精度的要求,可以为此类相机的研制提供一定的技术参考。     

Experimental evidence of the effect of heat flux on thomson scattering off ion acoustic waves

Thomson self-scattering measurements are performed in a preionized helium gas jet plasma at different locations along the laser propagation direction. A systematic and important variation of the intensity ratio between the blue and the red ion spectral components is observed, depending on whether the location of the probed region is in front of or behind the focal plane. A simple theoretical calculation of Thomson scattering shows that this behavior can be qualitatively understood in terms of a deformation of the electron distribution function due to the return current correlated with the classical thermal heat flux.     

出口雷诺数对平面射流自保持性的影响

通过实验研究出口雷诺数对平面湍流射流自保持性的影响. 测量的射流来自相同的喷嘴但不同的雷诺数Re（≡U_jh/ν,其中U_j是出口平均速度、h是窄缝出口的厚度和ν是黏性系数）,其变化范围是Re=4582—57735.所得的数据包括沿轴线的平均速度、湍流强度、积分尺度、高阶矩和能谱. 实验发现,随着Re的增大,平面射流发展减慢,平均速度和湍流强 关键词： 平面射流 雷诺数 自保持性     

Method of reconstructing wavefront aberrations from the intensity measurement

A method for reconstructing wavefront aberrations from intensity measurements in the focal plane of a focusing optic is presented. This reconstruction method is simple, fast, and accurate in reconstructing wavefront aberrations because it uses the inverse Fourier transform of an intensity distribution in the focal plane with a reference electric field. The validity of the reconstruction method is demonstrated by computing a wavefront aberration from the intensity distributions in the focal plane.     

Narrowing effect of focused polychromatic laser with small Fresnel number

Starting from Huygens-Fresnel diffraction integral, the field representation of focused polychromatic laser beams is derived. Intensity distributions of the focused polychromatic laser are investigated with different Fresnel number and bandwidth at focal plane. It is found that the width of transverse intensity distribution of the focused polychromatic laser decreases with increasing the bandwidth at the focal plane and zero local time, and the transverse intensity presents more obvious narrowing effects with smaller Fresnel number. A physical explanation for the narrowing effects is given based on a simplified expression.     

Diffraction Fields in the Focal Space of Symmetrical Hyperbolic Focusing Lens

The fields refracted by circular symmetric hyperbolic lens illuminated by a linearly polarized plane wave are calculated from the induced surface currents. It is shown that the fields in the axial region approximate to the fields in the aperture of corrugated horn under balanced hybrid condition. The image structures for different focal ratio are compared with the classical Airy pattern, deduced by scalar analysis, of optical focusing systems. The coupling between the lens and a corrugated horn at different position on focal plane are presented. The lens resolution and pix numbers are evaluated.