生物组织光学特性参数无损测量的模拟研究

生物组织的吸收系数和散射系数决定了组织表面的漫射光分布,但其理论关系式由于推导过程的近似及假设的边界条件不同,有几种不同的表示形式。为确定哪种表达形式更能精确地描述实际问题,本文给出了一种通过 Monte Carlo模拟进行校验的方法,确定了不同表达式的精确度,为进一步进行生物组织光学特性参数的无损测量打好基础。     

X-ray detection using the quantum-well exciton nonlinearity

Two related schemes for detecting X-rays based on (1) the scattering and (2) the reflection of a pulsed optical probe beam by carriers produced by the absorption of a single energetic X-ray photon are described. The detection method is based on the strong carrier density dependence of the (complex) index of refraction of the exciton absorption lines in a GaAs/AlGaAs multiple-quantum-well structure. These schemes can be used to construct a class of very sensitive gated X-ray detectors with micron spatial resolution and temporal resolution in the 10-30-ps regime     

Binary mask side lobe suppression using space scattering bar

Use of off-axis illumination such as dipole and cross-pole to obtain minimum dense pitch resolution limits process margin due to side lobe defect pattern formation. Side lobe or ghost images are unwanted additional patterns formed at wafer image at certain pitch range where intensity drop occurs [I. Hur, Proc. SPIE 2440 (1995) 278], and there are limited ways in which ghost images can be reduced. One way to suppress ghost image is to use multi-pole illumination and such an illumination condition is difficult to generate using diffractive optic elements so a hard aperture must be used but its use limits throughput. An alternative way is to vary the mask phase in order to somewhat increase the intensity to alleviate the formation at certain pitch range [H. Iwasaki et al., Proc. SPIE 3236 (1997) 544]. But for patterning memory devices at and below 50 nm half-pitch, it is shown that binary mask provides beneficial results over attenuated phase shift mask due so called “mask induced polarization effect” [A. Estroff et al., Proc. SPIE 5754 (2005) 555; W.H. Cheng et al., Proc. SPIE 5992 (2005) 1; S. Teuber et al., Proc. SPIE 5754 (2005) 543; Y. Aksenov et al., Proc. SPIE 5754 (2005) 576; I. Höllein et al., Proc. SPIE 5853 (2005) 194]. Nevertheless, optical proximity corrections are to be performed and maximum obtainable process margin need to be obtained. Hence, a method of optimizing space scattering assist feature positioning and sizing is discussed in this paper. A simplified analysis method to optimize space scattering assist feature insertion is formulated for an optical proximity correction. A simplified model formulation is defined a priori, and its result is compared to results obtained from an empirically calibrated model and indicated a good correlation.     

Quantifying spatial localization of optical mapping using Monte Carlo simulations

Optical mapping techniques used to study spatial distributions of cardiac activity can be divided into two categories. 1) Broad-field excitation method, in which hearts stained with voltage or calcium sensitive dyes are illuminated with broad-field excitation light and fluorescence is collected by image or photodiode arrays. 2) Laser scanning method, in which illumination uses a scanning laser and fluorescence is collected with a photomultiplier tube. The spatial localization of the fluorescence signal for these two methods is unknown and may depend upon light absorption and scattering at both excitation and emission wavelengths. We measured the absorption coefficients (micro a), scattering coefficients (micro s), and scattering anisotropy coefficients (g) at representative excitation and emission wavelengths in rabbit heart tissue stained with di-4-ANEPPS or co-stained with both Rh237 and Oregon Green 488 BAPTA 1. Monte Carlo models were then used to simulate absorption and scattering of excitation light and fluorescence emission light for both broad-field and laser methods in three-dimensional tissue. Contributions of local emissions throughout the tissue to fluorescence collected from the tissue surface were determined for both methods. Our results show that spatial localization depends on the light absorption and scattering in tissue and on the optical mapping method that is used. A tissue region larger than the laser beam or collecting area of the array element contributes to the optical recordings.     

差分吸收激光雷达几何因子实验确定方法

差分吸收激光雷达发射光束与接收视场的重叠区域用几何因子函数来描述,几何因子是差分吸收激光雷达的重要参数。提出了一种实验方法,实验使用米散射激光雷达和差分吸收激光雷达同时测量信号,通过对比分析两台激光雷达采集信号计算得到的气溶胶散射比廓线,获得差分吸收激光雷达的几何因子。该方法的优点在于不需要预先得到精确度高的激光雷达参数,比如望远镜直径,光束发散角,望远镜接收视场角等。该方法的应用有利于减少近地面差分吸收激光雷达测量臭氧廓线的误差,提高差分吸收激光雷达的探测性能,有助于研究近地面层的臭氧时空分布特征。     

Scattering-type near-field optical microscopy

A highly promising tool for nanoscale material characterization exploits local optical/infrared light scattering simultaneously with standard atomic force microscopy imaging. Thus, both the topography and the local optical/infrared properties of a sample surface can be mapped at better than 20 nm spatial resolution.     

基于均匀圆阵的宽频段二维零点预处理MUSIC算法

该文基于多圈均匀圆阵(UCA),在UCA-RB-MUSIC算法(Mathews等,1994)和一维零点预处理算法(魏平等人,1996)的基础上,提出了一种可任意设置响应零点的宽频段二维MUSIC算法,计算机仿真表明,该方法在保持了UCA-RB-MUSIC算法的高精度、高分辨力和降低了运算量的前提下,在宽频段内对于空间干扰信号的抑制有较好的效果。     

采用空间分辨漫反射测定胃组织光学特性

研究了人正常胃黏膜及黏膜下层组织对488 nm,514.5 nm,532 nm,630 nm和632.8 nm的激光的光学特性及其差异,实验采用空间分辨反射光和CCD探测器以及非线性拟合确定组织光学特性。结果表明,人正常胃黏膜及黏膜下层组织对五个波长的激光的吸收系数、约化散射系数、光学穿透深度、漫射系数、漫反射率和漫反射率的位移都是随着激光波长的变化而变化的。其吸收系数的最大值在532 nm,其值为0.482 mm-1,最小值在632.8 nm,其值为0.224 mm-1,最大差异在532 nm和632.8 nm之间,其值为115%,最小差异在488 nm和532 nm之间,其值为1.90%。其约化散射系数的最大值在488 nm,其值为5.93 mm-1,最小值在632.8 nm,其值为3.87 mm-1,最大差异在488 nm和632.8 nm之间,其值为53.2%,最小差异在514.5 nm和532 nm之间,其值为3.25%。其光学穿透深度的最大值在632.8 nm,其值为0.612 mm,最小值在488 nm,其值为0.341 mm。其漫射系数的最大值在632.8 nm,其值为0.084 mm,最小值在488 nm,其值为0.055 mm。其漫反射率的最大值在630 nm,其值为0.356,最小值在532 nm,其值为0.271。其Δx的最大值在632.8 nm,其值为0.153 mm,最小值在488 nm,其值为0.100 mm。可见,人正常胃黏膜/黏膜下层组织对五个波长的激光的光学特性参数存在明显的差异。     

Subpicosecond electrooptic sampling: Principles and applications

This paper reviews the principles and applications of electrooptic sampling for the characterization of repetitive ultrafast electrical transients. Electrooptic sampling is an electric field sensitive technique that utilizes ultrashort optical pulses as "sampling gates" via the Pockels effect in electrooptic media and has demonstrated subpicosecond temporal resolution and microvolt sensitivity. The technique can be adapted to characterize a wide variety of picosecond electronic devices such as field-effect transistors and photodetectors as well as probe complete integrated circuits with high temporal and spatial resolution.     

Analysis of picosecond pulse shape synthesis by spectral masking in a grating pulse compressor

This paper analyzes the synthesis of arbitrarily shaped optical pulses by spectral filtering in a fiber-and-grating pulse compressor. Spectral filtering of phase and amplitude is achieved by masking the spatially dispersed frequency components within the compressor. We show that the spectral filter is the convolution of the mask with the beam's transverse intensity profile. We discuss the effect of diffraction from the features of the physical mask, and show how finite spatial resolution limits the range of attainable temporal profiles. The fundamental limitation on spectral resolution is derived. Spectra and temporal pulse shapes corresponding to a variety of physical masks are calculated and are found to be in excellent agreement with experiments done with compressed pulses from a mode-locked Nd: YAG laser.     

由漫射图像测量生物组织的光学特性

为了获取生物组织的光学特性参量,采用CCD无损测量系统来获得生物组织的漫反射图像,通过数据分析获取组织表面的漫射光分布,首先对具有不同光学特性参最的组织模拟液进行测量,用实验所得数据训练神经网络,并用另一组实验数据对神经网络的有效性和精确度进行了验证,然后对牛肉、猪肉以及人体表皮组织在633nm光照下进行了测量,由经实...     

Frequency response theory for multilayer photodiodes

An exact solution is developed for the frequency response of photodiodes composed of multiple spatially uniform layers. Each layer is analyzed separately to obtain a set of linear response coefficients. The response of the multilayer diodes is calculated using matrix algebra. Effects of carrier transit, electron and hole trapping, avalanche decay, and finite absorption length are included in the analysis. The results of R.B. Emmons (1967) and G. Lucovsky et al. (1958) for avalanche photodiodes (APDs) and p-i-n's, respectively, are obtained as special cases. The theory is illustrated by applying it to the separated absorption and multiplication     

Comment on "Annealing behavior of a proton irradiated Al/sub x/Ga/sub 1-x/N/GaN high electron mobility transistors grown by MBE"

For original paper see S.J.Cai et al., ibid., vol.47, p.304-307 (2000). The paper by Cai et al. is the first article referring to radiation effects of Al/sub x/Ga/sub 1-x/N/GaN high electron mobility transistors published in this journal. In the paper, authors made use of the shifts of the decomposed three GaN Raman phonon modes E2 to analyze and explain the irradiation effects on GaN. However, we feel that incorrect assignment has been made to the decomposed E2 peaks in GaN and there are obvious errors in citing literature regarding Raman scattering shift rules that warrant comments.     

Principles of parametric temporal imaging. II. System performance

For pt. I, see ibid., vol. 36, p. 430, April 2000. The waveform manipulation technique known as temporal imaging can expand or compress signals in time while maintaining the shape of their envelope profiles. The temporal imaging system is analogous to that of its spatial counterpart, with dispersive propagation performing the role of diffraction and quadratic phase modulation in time acting as a “time lens.” Recent work has concentrated on time lenses produced by the parametric mixing of the dispersed input signal with a linearly chirped optical pump pulse because of the broad bandwidth, and thus fine temporal resolution, that can be obtained. In a previous paper, we presented the numerous parametric imaging configurations that are possible and drew temporal ray diagrams to illustrate their operation. In this paper, we study the performance of these systems. Resolution, field of view, number of resolvable features, and distortions particular to this approach are discussed     

海洋光学系统中的时空方法

海洋光学系统在海洋探索、开发和监测中起到了越来越重要的作用。水下无线光通信、水下激光雷达是两种迅速发展且有良好应用前景的海洋光学系统。水下无线光通信凭借高速率与低延迟的特点在中短距离应用中成为理想的通信选择;水下激光雷达在获取地理信息、目标探测等应用中也是常用的高精度、高效率的观测方法。然而,海水信道的复杂光学特性为海洋光学系统性能的进一步提升带来了挑战。在海水信道中,不仅吸收与散射作用较强,而且信道中可能有湍流、气泡等动态变化的干扰因素。为应对这些挑战,一方面可通过时间或空间方法提高信噪比;另一方面,时空信息转换的方法有利于提升系统的性能。文中对以上解决方案进行综述,并指出海洋光学系统的发展趋势。     

Lossy-to-lossless compression of medical volumetric data using three-dimensional integer wavelet transforms

We study lossy-to-lossless compression of medical volumetric data using three-dimensional (3-D) integer wavelet transforms. To achieve good lossy coding performance, it is important to have transforms that are unitary. In addition to the lifting approach, we first introduce a general 3-D integer wavelet packet transform structure that allows implicit bit shifting of wavelet coefficients to approximate a 3-D unitary transformation. We then focus on context modeling for efficient arithmetic coding of wavelet coefficients. Two state-of-the-art 3-D wavelet video coding techniques, namely, 3-D set partitioning in hierarchical trees (Kim et al., 2000) and 3-D embedded subband coding with optimal truncation (Xu et al., 2001), are modified and applied to compression of medical volumetric data, achieving the best performance published so far in the literature-both in terms of lossy and lossless compression.     

Diffuse optical multipatch technique for tissue oxygenation monitoring: clinical study in intensive care unit

Diffuse optical multipatch technique is used to assess spatial variations in absorption and scattering in biological tissue, by monitoring changes in the concentration of oxyhemoglobin and deoxyhemoglobin. In our preliminary study, the temporal tracings of tissue oxygenation are measured using diffuse optical multipatch measurement and a venous occlusion test, employing normal subjects and ICU patients suffering from sepsis and heart failure. In experiments, obvious differences in tissue oxygenation signals were observed among all three groups. This paper discusses the physiological relevance of tissue oxygenation with respect to disease.     

热作用致心肌组织在可见与近红外范围内的光学特性变化

研究了热作用对心肌组织在可见及近红外光谱范围内的光学特性改变。利用带积分球附件的分光光度计测量了心肌组织样品的漫反射率和总透射率,再用反向倍增(IAD)法从这两测量值中获取组织的吸收系数、约化散射系数和光学穿透深度。结果表明,自然的及热处理后的心肌组织的吸收系数、约化散射系数和光学穿透深度都是随着辐照波长的变化而显著变化的。自然的及热凝固后(80℃热处理)的心肌组织的吸收系数均在550 nm附近有一正峰,峰值分别为0.74 mm~(-1)和1.16 mm~(-1)。自然的心肌组织的约化散射系数在550 nm附近出现一正峰,峰值为0.25 mm~(-1);高温处理后此峰消失,而在590～625 nm出现上升坡。低温热处理对心肌组织的吸收系数没有明显的影响,高温热处理后心肌组织的吸收系数增大;心肌组织的约化散射系数随热处理的温度上升而显著地升高;心肌组织的光学穿透深度随热处理的温度上升而显著地减小。     

An accurate scheme for the solution of the time-domain Integral equations of electromagnetics using higher order vector bases and bandlimited extrapolation

Despite the numerous advances made in increasing the computational efficiency of time-domain integral equation (TDIE)-based solvers, the stability and accuracy of TDIE solvers remain problematic. This paper introduces a new numerical method for the accurate solution of TDIEs for scattering from arbitrary perfectly conducting surfaces. The work described in this paper uses the higher order divergence-conforming basis functions of Graglia et al. for spatial discretization and bandlimited interpolation functions for the temporal discretization of the relevant integral equations. Since the basis functions used for the temporal representation are noncausal, an extrapolation scheme is employed to recover the ability to solve the problem by marching on in time. Numerical results demonstrate that the proposed method is stable and that it exhibits superlinear convergence with regard to the spatial discretization and exponential convergence with respect to the temporal discretization.     

基于水体退化函数补偿方法的水下傅里叶单像素成像

水下光学成像的探测环境相对复杂。前向散射、后向散射和吸收极大地降低了水下光学成像的成像质量。单像素成像因其较高的抗噪声性而被认为是一种适合于水下光学成像的技术。对于水下单像素成像系统,目前存在的问题是需要采用结构光进行照明,当散斑在水下传播时,前向散射会使预先生成的散斑发生畸变。因此,重建结果的分辨率降低,重建结果模糊不清。为了减小前向散射对单像素成像系统的影响,对傅里叶单像素成像的重建过程进行改进。在空间谱域傅里叶单像素成像系统的水下退化函数进行估计,然后根据估计的退化函数实现目标空间谱反演。最后利用傅里叶变换对反演后的目标空间谱进行变换,最终获得目标的强度图像。理论分析和实验结果证明了该方法的有效性。利用该方法,能够有效地减小前向散射对成像质量的影响,提高了水下傅里叶单像元成像的重建结果质量。