Vibration of a parallelogram membrane

The approximate natural frequencies of oblique membranes have been determined for arbitrary skew angles and side ratios. The response of such a membrane to a forcing function is then obtained in a similar fashion. The lower natural frequencies have been presented for various side ratios of the membrane as a function of the skew angle and vice versa. With increasing skew angle they increase rapidly. For large skew angles the lower natural frequencies are mainly made up by those of the index n = 1. This is especially valid for membranes of large side ratio.     

波前编码显微物镜景深扩展的研究

为了解决传统显微物镜景深与分辨率的矛盾,采用波前编码的方法,设计研究了波前编码的10倍显微物镜,结合传统光学设计软件,采用基于MTF一致性的相位板参数的优化方法,实现了在像面附近一定范围内系统的点扩散函数一致性;此外,还设计了扩展三次相位编码板的10倍显微物镜,比较了采用两种不同相位板系统的焦深扩展的效果,结果显示三次相位板的焦深扩展效果较好,可以将传统10倍显微物镜的焦深扩展15倍。成像模拟仿真结果显示滤波后的编码像在±15倍焦深范围内成像清晰,从而扩大了系统的景深。     

基于SLM的计算全息三维显示视角扩展编码

提出一种利用高分辨液晶空间光调制器的高衍射级来增大再现视角的计算全息编码方法.该方法首先对被记录物波的视角超出所用高分辨液晶空间光调制器允许范围的物波信息进行预处理,使预处理后的物波视角满足抽样定理;然后再进行计算全息编码.这种计算全息图可利用高分辨液晶空间光调制器的特定高衍射级恢复再现被记录物波.文中给出了该方法的编码原理及物波函数的预处理公式,并通过设计实例和实验结果证明了该方法的可行性.     

基于光学系统像面分割的图像恢复方法研究

实际光学系统的点扩散函数随视场的不同而变化,因此基于线性不变成像系统的图像恢复方法在处理由大视场系统得到的图像时,恢复效果不理想。若把成像系统作为线性空变系统来进行处理,根据等晕成像原理,如将降质图像分割为不同区域进行复原的话,则可以有效地提高图像的恢复效果。针对区域间边界不连续性的问题,提出了区域延拓的解决方法,通过数字仿真,验证了图像分割处理与区域延拓方法的可行性。     

Calibrating the HXMT collimators using diffuse illumination

We propose a new method to calibrate the HXMT collimators by measuring the optical point spread function (PSF) of the hard X-ray modulation telescope (HXMT). The light transmission of the collimator at different viewing angles with a camera and a diffuse backlight placed behind the collimator is measured. This method is much easier to accomplish than measuring the PSF with a parallel optical beam. The experimental results are very consistent with the simulations. The PSF of the collimator of the high energy X-ray telescope on HXMT is found to be in good agreement with the design, with accuracy better than 1 arcmin.     

全视角高精度三维测量仪光学系统误差分析研究

大视角、高分辨率、低畸变光学成像系统是全视角高精度三维测量仪中最为关键的核心器件。现有三维测量仪实际使用过程中不可避免会产生各种误差,因此科学合理地评估和降低全视角高精度三维测量仪的测量误差具有十分重要的科学及工程应用意义。通过多角度、全方面分析定量研究了相机内方位元素标定误差对几何定位误差的影响,以及相机光学系统MTF分析、点扩散函数分析、波像差分析和公差分析对匹配误差产生的影响。研究结果表明,在各种影响三维测量仪光学成像系统测量误差的因素当中,相机的传递函数是影响系统三维定位误差最主要的因素,当系统MTF_N值大于0.4 lp/mm、系统几何畸变小于1个像素,PSF能量集中在以3 μm为半径的圆环内(小于1个像素),且PSF峰值达到了0.9时,三维测量仪的定位误差可达到秒级精度。     

盐渍化土壤偏振高光谱信息与土壤线的关系初探

正确评价土壤盐渍化对地区农业生产与生态环境具有重要意义。土壤线对土壤盐渍化程度具有一定的指示作用,但在不同角度下观察获得的土壤光谱特征会发生变化,土壤线的参数值也会随之变化。依据以实验室测定的盐渍化土壤多角度偏振高光谱反射率,分析并确定土壤盐渍化程度与土壤线参数之间的关系,初步探求在偏振反射条件下土壤线最佳的获取方式。结果表明：(1)土壤光谱反射率随波段的增加逐步缓慢上升,趋于平缓。随着盐渍化程度的增强,土壤的光谱反射率先逐步降低至某一临界值后又逐步升高;(2)土壤的盐渍化程度与土壤线的斜率和截距均呈线性相关,随着盐渍化程度的增强,土壤线的斜率变小,截距变大;(3)探测天顶角影响偏振状态与土壤线参数的关系,当探测天顶角一定时,偏振状态与土壤线参数之间具有规律性。探测天顶角在0°-50°之间,随角度的变大,土壤线斜率变大,截距变小;(4)偏振状态影响土壤线参数与土壤盐渍化程度的相关性程度,初步确立偏振角度为90°,探测天顶角为25°状态下,建立的土壤盐渍化程度与土壤线参数关系模型较优。为定量反演土壤盐渍化程度提供新的途径。可以用于土壤的盐渍化程度评价。     

倾斜入射的波前编码系统的点扩散函数扩大效应分析

通过对坐标系统进行旋转，计算得到了三次型波前编码系统的倾斜入射的光瞳函数，并给出了近似表达式. 分析表明倾斜入射会产生三次相位扩大效应和离焦扩大效应，它们和入射角的正负无关，且随着入射角绝对值的增大而增大. 这表现在点扩散函数(point spread function, PSF)上会扩展PSF包络的两条直角边，表现在调制传递函数(modulation transfer function, MTF)上会降低MTF值. 子午面倾斜入射时，子午方向的三次相位扩大效应和离焦放大效应大于弧矢方向，从而导致子午方向     

倾斜入射的波前编码系统的点扩散函数扩大效应分析

通过对坐标系统进行旋转,计算得到了三次型波前编码系统的倾斜入射的光瞳函数,并给出了近似表达式. 分析表明倾斜入射会产生三次相位扩大效应和离焦扩大效应,它们和入射角的正负无关,且随着入射角绝对值的增大而增大. 这表现在点扩散函数(point spread function, PSF)上会扩展PSF包络的两条直角边,表现在调制传递函数(modulation transfer function, MTF)上会降低MTF值. 子午面倾斜入射时,子午方向的三次相位扩大效应和离焦放大效应大于弧矢方向,从而导致子午方向 关键词： 倾斜入射 波前编码 三次相位扩大效应 离焦扩大效应     

植物叶片润湿性与光谱反射偏振度关系研究

城市绿化植物由于其滞尘能力能够有效改善城市大气环境，滞尘能力的主要影响因素是其表面特性和润湿性。植物叶片表面的润湿性和偏振反射特性都与表面粗糙度相关，因此以粗糙度为结点，探究植物表面润湿性与偏振反射光谱的关系，利用偏振反射特性对植物叶片润湿性进行快速无损监测。以长春市常见的八种绿色植物叶片为研究对象，利用Kruss DSA 100液滴形状分析系统测量其表面接触角，利用多角度光谱测量装置测量其在不同探测天顶角上的偏振反射光谱，探讨了润湿性能在400～1 000 nm波段对植物叶片不同探测天顶角上偏振度的影响。通过相关分析确定八种植物叶片的特征波段，并在特征波段对偏振度随探测天顶角的变化程度与润湿性的关系之间进行定量分析。结果表明，在特征波段(700±10) nm处，偏振度随着探测天顶角的变化程度θ₀与接触角距离100°的偏差值θ具有很强的相关性，可决系数R2为0.82，说明偏振度随探测天顶角的变化程度θ₀可以反映植物叶片的润湿性，可以利用偏振反射特性对植物叶片润湿性进行分析，研究成果将对今后城市绿化物种的选择提供可行性建议。     

共焦扫描显微成象系统的点扩散函数再商讨

针对共焦扫描显微成象中物体相对于被扫描点的位置矢量是反向移动的特性,探讨了物体移动后的物函数在此基础上,根据成象的理论进行了计算,得到新的系统点扩散函数表达式,最后根据计算结果分析成象的性质,得出了系统成象的相干性.     

Improvement of the outcoupling efficiency of an organic light-emitting device by attaching microstructured films

In this paper, we present and analyse the optical characteristics, such as spectral shift, CIE coordinates, viewing angle dependence, luminous current efficiency and luminous power efficiency, of an organic light-emitting device (OLED) with a commercial diffuser film or a brightness-enhancement film (BEF) attached. Compared to a planar green OLED, the luminous current efficiencies of the OLED with an attached diffuser film or BEF increase by 29% and 23%, respectively. The overall luminous power efficiencies are enhanced by 28% and 7%. Compared to the planar green device, we observe blue shifts at different viewing angles when microstructured films are attached, which is the evidence that the waveguiding modes are being extracted. In our planar OLED, the peak wavelength blue shifts and the full width at the half maximum (FWHM) decrease with increasing viewing angles due to the microcavity effect. When the diffuser is attached, the spectral peak has a constant blue shift (6 nm) compared to that of the planar OLED. On the other hand, in the BEF case, the spectral shift depends on the viewing angle (2-12 nm blue shifts from 0 to 80°). This is due to the different operating principles (scattering and redirected light) of the diffuser and BEF. Since the transmittance spectra of both the diffuser film and the BEF are flat over the visible range, it is suitable for lighting applications by using white OLED. When attaching the films on a commercial white OLED, the luminous current efficiencies of the OLED with an attached diffuser film or BEF increase by 34% and 31%, respectively. The overall luminous power efficiencies are enhanced by 42% and 8%.     

一种优化波前编码系统相位板参数的新方法

根据波前编码系统的设计理论,在兼顾图像恢复能力的基础上,提出利用不同离焦距离的点扩散函数与焦面处的点扩散函数之间的希尔伯特空间角作为成像特性一致性的评价函数,结合遗传算法,对扩大景深的波前编码成像系统的相位板参数进行优化。分别在空间域和频率域上分析应用波前编码技术前后光学系统的成像特性,并利用最小二乘数字滤波器对中间模糊图像进行复原。仿真实验结果表明:在三次相位板上应用此方法获得的最佳相位板参数使波前编码系统焦深扩展了10倍。     

Phase-encoding strategies for optimal spatial resolution and T1 accuracy in 3D Look-Locker imaging

The Look-Locker (LL) imaging method provides an accurate and efficient approach for mapping the spin-lattice relaxation time, T(1). However, the same recovery of signal during LL image acquisition required to estimate T(1) also results in unwanted modulation of k-space. This is particularly problematic with 3D LL imaging as the number of phase-encoding steps during the recovery interval (e.g., 16) increases in an effort to reduce imaging times. This modulation of k-space has the effect of introducing a point spread function (PSF), which can lead to either image blurring (if the earlier tip angles are assigned to the centre of k-space) or edge enhancement (if the earlier tip angles are assigned to the edges of k-space), thus corrupting T(1) estimation, particularly for small objects. In this study, the PSF and its effect on the acquired images for four different interleaved phase-encode schemes (centric-in, centric-out, sequential and hybrid-sequential) are simulated for a range of T(1), tip angle and 3D LL acquisition parameters expected in practice. It is shown by simulation and confirmed experimentally in phantoms that a hybrid sequential phase-encoding scheme reduces image blurring while maintaining T(1) accuracy ( approximately 2%) and precision (2%) over a range of object sizes down to 2 pixels (2 mm).     

背投系统视角计算方法研究

介绍了一种计算背投系统视角的方法,可用来衡量背投系统性能.背投系统的视角不仅仅依赖于背投屏幕,也与光学引擎和观看环境有关.综合这三个方面的因素得到背投系统的对比度和角度的关系,根据人眼能接受的最小对比度可推算出背投系统的视角.实验数据表明,根据方法中表达式计算所得视角与实际参量吻合较好,证明该计算方法简单有效.     

偏振光谱的土壤湿度遥感方法实验研究

偏振探测作为一种新型遥感技术,是对传统光谱遥感探测的有益补充,为目标遥感探测提供更丰富的信息。用地物偏振光谱仪实验测量,分析土壤湿度与偏振光谱的相关性,同时研究不同观测角下的土壤表面反射光偏振光谱特性。结果表明：在土壤湿度较高的情况下,偏振光谱与土壤湿度具有一定的相关性,尤其在500～700 nm波段,湿度与偏振度呈正比关系;低湿度的情况下,偏振光谱与土壤湿度相关性不明显;此外,不同观测角对偏振光谱也有影响,如入射角固定为50°,观测角在20°～60°区间测量时,偏振度随观测角增大而增大,且观测角愈大,偏振度随湿度的变化愈显著。     

The influence of skew rays on angular losses in air-clad fibres

Detailed experimental transmission properties of high numerical aperture air-clad undoped fibres are presented. Measurements of the angular transmissivity indicate a 15% lower numerical aperture (NA = 0.75) compared to theoretical predictions for the bridge thickness and wavelength ratio of δ/λ = 0.226. The discrepancy is attributed to skew rays that are deliberately launched and which are subject to larger loss rates through diffractive tunnelling in frustrated total internal reflection than meridional rays. Measurements of the angular propagation losses show that light launched at angles less than the critical angle for total internal reflection experiences low initial losses as well as low propagation losses. Light launched at steeper angles experiences a significant initial loss attributed to loss of skew rays within 1.5 m of propagation as well as larger general propagation losses.     

Pupil design based on Fisher information optimization to extend field depth in practical optical system

<正>Wavefront coding(WFC) is used to extend the field depth of an incoherent optical system by employing a phase mask on the pupil.We uses a Fisher information(FI) metric based optimization method to design a phase mask by taking the modulation transfer function(MTF) of the practical optical system into consideration. This method can modulate the wavefront so that the point spread function and optical transfer function are insensitive to the object distance.The simulation results show that the optimized phase mask based on the proposed method can further improve the defocusing image quality while maintaining the focusing image quality.     

轴锥镜成像系统的点扩散函数分析

为了使大景深光学镜头在工业视觉检测中的测量结果更准确,必须对中间图像进行复原,点扩散函数是图像复原的关键。根据轴锥镜最大无衍射距离公式设计了无衍射成像系统,以标量衍射理论为基础,在频域范围内利用稳定相法推导出系统的点扩散函数公式。利用准单色光理论,分析非相干光照明下的点扩散函数与锥镜夹角和离焦量的关系。仿真和实验结果表明:轴锥镜夹角越大,点扩散函数中心光强越强,衍射条纹越密;离焦像差对点扩散函数的影响与之相反。     

相位板装配倾斜对波前编码系统点扩散函数的影响

分析了装配误差引起的相位板倾斜对波前编码系统的影响,通过坐标变换推导了相应条件下的广义光瞳函数。结果表明：倾斜因子对系统的相位板系数具有放大效果,其随倾斜角绝对值的增大而增大,而与倾斜角的正负无关。相位板倾斜会放大系统点扩散函数包络面的两条直角边,相应地降低其光学传递函数值。在子午倾斜的条件下,子午方向的相位板系数放大效果大于弧矢方向,从而导致点扩散函数包络面在子午方向的放大效果大于弧矢方向,子午方向光学传递函数值的降低效果大于弧矢方向。采用MATLAB以及商用光学软件进行仿真实验,验证了上述结论。