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1.
刘兰琴  粟敬钦  罗斌  王文义  景峰  魏晓峰 《物理学报》2007,56(11):6749-6753
建立了宽带激光脉冲放大的物理模型.模型引入交叉弛豫时间表征不同频率响应下反转粒子与激光作用后重新形成分布的快慢,模型考虑的整体非均匀加宽、局部均匀加宽的混合加宽机理弥补了现有放大模型仅考虑均匀加宽的不足.基于此物理模型,开发了宽带激光传输放大的模拟设计软件CPAP,并讨论了在一定条件下此宽带模型可回归到窄带模型.  相似文献   

2.
从相干激光测风雷达原理入手,论述了激光雷达回波特性和多普勒效应在测风雷达中的应用。基于大气分层模型,考虑到激光束的传播及其与大气之间的相互作用,建立了激光测风雷达回波模型,模拟回波信号在大气中的传输过程,为激光测风雷达回波信号的模拟提供了理论基础。  相似文献   

3.
激光诱导间质热疗手术方案的制定需要术前对引入激光能量在组织中的分布进行准确的数值模拟。考虑肿瘤大小、光学特性与周围正常组织的差别,建立激光诱导间质热疗时的肿瘤与正常组织两层结构模型,采用蒙特卡罗方法模拟激光在其中的传播,得到激光能量在组织中的分布规律,并采用Pennes生物传热方程计算得出组织的稳态温度分布,这对于激光诱导间质热疗的临床应用具有积极的理论指导意义。  相似文献   

4.
线激光束均匀化整形方法研究   总被引:4,自引:0,他引:4       下载免费PDF全文
为解决核物理工程、表面热处理、激光加工、激光通信中传输激光束的均匀性问题,提出采用三角楔柱透镜改善线激光均匀性的新方法,并在ZEMAX开发环境下建立了整形光路系统的理论模型。利用所建立的模型,分析了整形柱透镜在不同半径、斜面夹角、透镜介质折射率等参数下光束的均匀性。研究表明:在远场条件下,通过改变整形柱透镜的参数,能够得到能量分布均匀的线激光。在实际应用中,可以采用1个半圆柱和2个相同三角楔胶合成型的简单工艺。进一步模拟发现,两种整形系统所得到的均匀度和线宽一致。  相似文献   

5.
激光热疗中生物组织的光热描述及研究进展   总被引:4,自引:0,他引:4  
《物理》2000,29(4):228-231,241
激光热疗中,激光与生物组织相互作用研究应包含两个方面:一是光子在生物组织中的迁移规律,基于传输理论的Monte-Carlo方法能较为真实地模拟光在生物组织内的分布,并进一步获得热源的分布;另一方面是热在生物组织中的传导,经典的Pennes方程和基于微结构的Weinbaum与Jiji模型从不同层面描述生物组织中的传热问题,两者的统一是至关重要的,文中对此进行了阐述,文中还报道了用光学方法对组织热凝固  相似文献   

6.
大气环境下激光传输仿真软件的设计与编制   总被引:1,自引:0,他引:1  
随着激光技术的发展,激光大气传输特性一直是激光领域的研究热点。综合激光大气传输的理论模型,运用科学的软件开发方法设计出了一套仿真系统,用来模拟激光在复杂大气环境中的辐射特性和激光的传输过程。该系统理论模型以Lambert-Beer定律为基础,结合了瑞利散射和米散射等经典理论,当在烟幕环境中模拟激光传输时,采用了多次散射模型。仿真中对大气环境采用逐段细化,每段根据数据库参数变化选取合适的计算模型,以提高仿真精度。绘制出了光斑和等位面随传输距离的演化图形,以演示激光大气的传输过程。  相似文献   

7.
本文以超短脉冲激光照射参与性介质的光学成像为研究背景,分别构建了短脉冲激光在参与性介质内的频域辐射传输正问题模型和根据边界探测所得频域信号重建介质内部光学参数的逆问题模型。在瞬态辐射传输方程的基础上,利用傅里叶变换得到频域辐射传输方程,采用有限体积法求解频域传输方程,模拟超短脉冲激光在二维参与性介质内传输的过程,得到介质边界的出射频域辐射信号。选取共轭梯度法作为反演算法,采用伴随差分模型求解目标函数梯度,重建了二维非均匀参与性介质内不同位置内含物的光学参数分布。结果表明,基于频域辐射传输方程的伴随差分模型能够较为准确地反演多维参与性介质内的光学参数。  相似文献   

8.
季小玲  邓宇 《强激光与粒子束》2021,33(8):081002-1-081002-12
地基激光空间碎片清除和利用激光辐射把转换的太阳能从空间轨道输运到地面等应用中,不可避免地遇到高功率激光在非均匀大气中的传输问题。由于激光功率已远远超过大气非线性自聚焦临界功率,大气自聚焦效应是影响光束质量的一个重要物理因素。概述了近年来国内外高功率激光在非均匀大气中上行或下行传输的自聚焦效应研究进展,主要介绍了高功率激光在非均匀大气中的传输模型、理论基础、数值和解析研究方法,着重介绍了自聚焦效应对激光传输特性和光束质量的影响,并总结了优化靶面光束质量的方案。此外,还介绍了大气群速度色散效应和大气湍流效应等物理因素对激光光束质量的影响。最后,还提出了该领域值得进一步深入研究的一些问题。  相似文献   

9.
提出利用非相干单色发光二极管(LED)光源和多模光纤产生空心光束。证实了将LED光源以一定角度倾斜耦合进大芯径多模光纤可获得光斑均匀的空心光束。分析了光束在多模光纤中的传输路径和产生空心光束的机理,并用Zemax软件建立仿真模型进行模拟。搭建利用LED和多模光纤产生空心光束的实验系统并且与激光作为光源产生的空心光束进行分析比较,结果表明利用LED光源获得的空心光束均匀性更好。  相似文献   

10.
大气对激光传输的影响   总被引:4,自引:0,他引:4  
本文分析了激光传输过程中大气这一传输介质对其的影响,由大气的成分出发,采用辐射传输理论描述了大气介质的吸收和散射特性,着重分析了其中对辐射影响最大的两种因素,即大气消光和大气湍流。并建立了大气传输系统的传递函数模型。最后通过LOWTRAN模拟软件包对本文所得的模型进行评估。  相似文献   

11.
测量组织局部血液灌注率的表面热干扰法   总被引:1,自引:0,他引:1  
1日u云去正常的血液灌注是机体组织重要的生理要素之一,组织所需的氧、营养和药物靠灌注的血液来运输供应。心肌缺血(即冠心病)是当前困扰人们的发病率高的严重疾病之一。脑对血液的供应则更是敏感,脑血管的局部栓塞将导致局部脑组织缺血甚至坏死。因此,组织灌注状况的检测不仅对于生理和病理研究是重要的,对临床医学也是十分重要的。事实上,某些非缺血性疾病的治疗(例如癌瘤的热疗)过程也直接或间接地涉及到组织的灌注率。寻求一种测量组织灌注率的方法一直是人们孜孜以求的。近年来,各种测量方法的研究已有相当的发展山,其中热…  相似文献   

12.
Finite difference simulations have been used to model (3)He gas diffusion in simulated lung tissue. The technique has the advantage that a wide range of structural models and diffusion-sensitizing gradient waveforms can be investigated, for which analytical methods would otherwise be virtually impossible. Results from simulations and in vivo pulsed-gradient-spin-echo (PGSE) experiments show that the apparent diffusion coefficient (ADC) is a function of diffusion time and gradient strength, and suggests diffusion is locally anisotropic. The simulations have been compared to recent work on an analytical model that characterizes lung tissue as a series of independent cylinders. The results presented may have clinical implications for (3)He ADC measurements in assessing lung diseases such as chronic-obstructive-pulmonary-disease.  相似文献   

13.
For the first time, the influence of hyperthermic regional perfusion therapy on tumor cell metabolism has been monitored by means of 31P MR spectroscopy. Shortly after treatment, a complete depletion of high energy phosphates, a significant increase of inorganic phosphate, phosphomono- and phosphodiester resonances and a decrease of pH have been observed. Healthy muscle tissue showed only minor effects caused by this aggressive therapy. The time course of the transient variation of phosphate metabolite concentrations is explained in the framework of a simple pathophysiological model. The results demonstrate that the imediate effect of chemotherapy on tumor tissue can be detected by 31P MRS before any clinical signs of tumor response are visible.  相似文献   

14.
The vocal-fold tissue is treated as a transversally isotropic fluid-saturated porous material. Effects of poroelastic coefficients on eigenfrequencies and eigenmodes of the vocal-fold vibration are investigated using the Ritz method. The study demonstrates that the often-used elastic model is only a particular case of the poroelastic model with an infinite fluid-solid mass coupling parameter. The elastic model may be considered appropriate for the vocal-fold tissue when the absolute value of the fluid-solid mass coupling parameter is larger than 10(5) kg/m(3). Otherwise, the poroelastic model may be more accurate. The degree of compressibility of the vocal tissue can also been described by the poroelastic coefficients. Finally, it is revealed that the liquid and solid components in a poroelastic model could have different modal shapes when the coupling between them is weak. The mode decoupling could cause desynchronization and irregular vibration of the folds.  相似文献   

15.
A detailed analysis procedure is described for evaluating rates of volumetric change in brain structures based on structural magnetic resonance (MR) images. In this procedure, a series of image processing tools have been employed to address the problems encountered in measuring rates of change based on structural MR images. These tools include an algorithm for intensity non-uniformity correction, a robust algorithm for three-dimensional image registration with sub-voxel precision and an algorithm for brain tissue segmentation. However, a unique feature in the procedure is the use of a fractional volume model that has been developed to provide a quantitative measure for the partial volume effect. With this model, the fractional constituent tissue volumes are evaluated for voxels at the tissue boundary that manifest partial volume effect, thus allowing tissue boundaries be defined at a sub-voxel level and in an automated fashion. Validation studies are presented on key algorithms including segmentation and registration. An overall assessment of the method is provided through the evaluation of the rates of brain atrophy in a group of normal elderly subjects for which the rate of brain atrophy due to normal aging is predictably small. An application of the method is given in Part II where the rates of brain atrophy in various brain regions are studied in relation to normal aging and Alzheimer's disease.  相似文献   

16.
Scroll waves are vortices that occur in three-dimensional excitable media. Scroll waves have been observed in a variety of systems including cardiac tissue, where they are associated with cardiac arrhythmias. The disorganization of scroll waves into chaotic behavior is thought to be the mechanism of ventricular fibrillation, which lethality is widely known. One of the possible mechanisms of scroll wave instability is negative filament tension, which was studied theoretically using low-dimensional models of excitable medium. In this article we perform a numerical study of negative filament tension using the Luo-Rudy phase 1 model, which is widely used in cardiac electrophysiology. We show that this instability exists in this model, study its manifestation and discuss its relation to cardiac arrhythmogenesis.  相似文献   

17.
Multiexponential transverse relaxation in tissue has been interpreted as a marker of water compartmentation. Articular cartilage has been reported to exhibit such relaxation in several studies, with the relative contributions of tissue heterogeneity and tissue microstructure remaining unspecified. In bovine nasal cartilage, conflicting data regarding the existence of multiexponential relaxation have been reported. Imaging and analysis artifacts as well as rapid chemical exchange between tissue compartments have been identified as potential causes for this discrepancy. Here, we find that disruption of cartilage microstructure by freeze-thawing can greatly alter the character of transverse relaxation in this tissue. We conclude that fresh cartilage exhibits multiexponential relaxation based upon its microstructural water compartments, but that multiexponentiality can be lost or rendered undetectable by freeze-thawing. In addition, we find that increasing chemical exchange by raising sample temperature from 4°C to 37°C does not substantially limit the ability to detect multiexponential relaxation.  相似文献   

18.
In periodontology and implantology, laser-induced cavitation has not yet been used to treat biofilm-related problems. In this study we have checked how soft tissue affects the evolution of cavitation in a wedge model representing periodontal and peri-implant pocket geometry. One side of the wedge model was composed of PDMS mimicking soft periodontal or peri-implant biological tissue, the other side was composed of glass mimicking hard tooth root or implant surface, which allowed observations of the cavitation dynamics with an ultrafast camera. Different laser pulse modalities, PDMS stiffness, and irrigants were tested for their effect on the evolution of cavitation in the narrow wedge geometry. The PDMS stiffness varied in a range that corresponds to severely inflamed, moderately inflamed, or healthy gingival tissue as determined by a panel of dentists. The results imply that deformation of the soft boundary has a major effect on the Er:YAG laser-induced cavitation. The softer the boundary, the less effective the cavitation. We show that in a stiffer gingival tissues model, photoacoustic energy can be guided and focused at the tip of the wedge model, where it enables generation of secondary cavitation and more effective microstreaming. The secondary cavitation was absent in severely inflamed gingival model tissue, but could be induced with a dual-pulse AutoSWEEPS laser modality. This should in principle increase cleaning efficiency in the narrow geometries such as those found in the periodontal and peri-implant pockets and may lead to more predictable treatment outcomes.  相似文献   

19.
An isointense model has been developed to evaluate the applicability of putative tumor-specific MRI contrast agents. Data for tissue relaxation measurements in the presence of Mn(III)TPPS4 are used to illustrate the model. The concentration of contrast agent in tumor tissue required for a tumor/normal tissue signal difference-to-noise ratio of 5 (delta SNR = 5) is determined for a T1 weighted pulse sequence and several hypothetical tumor/normal tissue pairs. The impact of various contrast agent characteristics including initial tumor/normal tissue relaxation values, differential uptake of contrast agent, and in vivo relaxivity are considered. Isointense tumor/normal tissue with longer initial relaxation times are shown to be more affected by the presence of contrast agent. In addition those with initially longer relaxation times have less rigorous requirements for tumor specificity. Typically, a normal tissue/tumor uptake ratio of 1:2 increases the concentration required for delta SNR = 5 by a factor of two compared to that of exclusive uptake in tumor. For the T1 weighted pulse sequence employed, the concentration required for delta SNR = 5 is shown to be linear with the inverse of in vivo relaxivity for the hypothetical tissues considered. The isointense model is also extended to predict the field dependence of tumor-specific contrast enhancement by Mn(III)TPPS4.  相似文献   

20.
The transducers of diagnostic ultrasonic equipment generate undesired local heating at the applied part of the transducer surface. The assessment of this heating is fundamental in warranting patient safety. On the standard IEC 60601-2-37, methods have been established for the reliable measurement of heating, where three tissue models based on tissue-mimicking materials are recommended: soft tissue mimic only, bone mimic close to the surface of soft tissue, and skin mimic at the surface of soft tissue. In the present work, we compared the last-mentioned tissue model with a new one using a layer of porcine subcutaneous fat inserted between the soft tissue and skin-mimicking materials. We verify significant statistical differences between models, with the average temperature rise measured for the tests without subcutaneous fat at 6.7 °C ± 1.7 °C and for the ones with subcutaneous fat at 8.9 °C ± 1.8 °C (k = 2; p = 0.95). For each model, the procedure was performed 10 times in repeatability conditions of measurement. It has been suggested that the influence of subcutaneous fat for external transducers heating evaluation should be considered, as the presence of many millimeters of subcutaneous fat is a common condition in patients. Otherwise, the transducer surface heating and, therefore, the risk to the patient may be underestimated.  相似文献   

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