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## 电子代写|光纤代写Optical Fiber代考|PHOTOMULTIPLIER

A PMT is a vacuum tube that employs the photoelectric effect as well as the secondary emission of electrons to provide high current gain. A schematic representation of the PMT tube is given in Figure 3.6. When photon reaches the photocathode, which is made of a low work-function metal or semiconductor, then if the photon energy exceeds the work function, the electron will be ejected with a certain probability. After the ejection, electron is accelerated by the electric field formed between the series of electrodes called dynodes. The dynodes are coated with a material that is prone to secondary emission of electrons and are connected in series between the resistors. The resistors $R$ that are connected in series between the dynodes form the gradient of voltage from the high voltage source $+V_{\mathrm{HV}}$ to the ground. The dynodes generate additional electrons by the secondary emission. Finally, all the electrons that are generated by the dynodes are captured by the anode. The current multiplication process continues for each dynode in the PMT tube, thus providing the current gain that can exceed $10^6$.

The probability of detecting incident photon is equal to the quantum efficiency of the PMT tube. Typical photocathode can reach a quantum efficiency of $30 \%$ meaning that in average approximately every third photon is detected.

PMTs are usually used for the laboratory instrumentation. Due to their very high current gain, the PMT tubes are used to detect extremely low optical signals. PMTs are physically large, require high voltage power supplies, and are mechanically fragile.

## 电子代写|光纤代写Optical Fiber代考|PHOTOCONDUCTORS

Photoconductors employ the photon absorption in semiconductor material. There are three principal absorption processes that can be found in semiconductors, as presented in Figure 3.7. The intrinsic band-to-band absorption appears in the cases when the bandgap energy $E_G$ of the material is lower than the photon energy. Therefore, the photon is able to excite the electron from the valence to the conduction band. Such obtained hole and electron constitute a charge carrier. If an external electric field is applied, the hole and electron propagate throughout the semiconductor material to the external circuit thus causing photocurrent flow.

Intrinsic band-to-band absorption represents a dominant absorption mechanism in most semiconductors which are used for the photodetection purposes. To trigger the intrinsic band-to-band absorption, the following condition must be fulfilled:

\begin{aligned} &h v>E_G \ &\frac{h c}{\lambda}>E_G \end{aligned}
where $h v$ is the photon energy. According to eq $3.14$, there is a maximum wavelength where the intrinsic band-to-band absorption still can occur. This maximum wavelength is given by:
$$\lambda_{\max }=\frac{h c}{E_G} .$$

## 电子代写|光纤代写光纤代考|PHOTOMULTIPLIER

PMT是一种利用光电效应以及电子的二次发射来提供高电流增益的真空管。PMT管的示意图如图3.6所示。当光子到达由低功函数金属或半导体制成的光电阴极时，如果光子能量超过了功函数，电子就会以一定的概率被弹出。弹射后，电子被一系列电极之间形成的电场加速。dynode被一种易于电子二次发射的材料覆盖，并在电阻之间串联连接。在dynode之间串联的电阻$R$形成了从高压源$+V_{\mathrm{HV}}$到地面的电压梯度。dynode通过二次发射产生额外的电子。最后，所有dynode产生的电子都被阳极捕获。对于PMT管中的每个dynode，当前的乘法过程继续进行，从而提供可以超过$10^6$ .的电流增益

pmt通常用于实验室仪器。由于其非常高的电流增益，PMT管用于检测极低的光信号。pmt在物理上很大，需要高压电源，而且在机械上很脆弱

## 电子代写|光纤代写光纤代考| photoconductor

\begin{aligned} &h v>E_G \ &\frac{h c}{\lambda}>E_G \end{aligned}

$$\lambda_{\max }=\frac{h c}{E_G} .$$

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。

Posted on Categories:Optical Fiber, 光纤, 电子代写

## avatest™帮您通过考试

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## 电子代写|光纤代写Optical Fiber代考|PHOTOMETRY

In photometry, the light is measured in such a way that the measurement result is in accordance with the human vision. A large number of devices are aimed for human use such as computer displays, TVs, and traffic signal lights, therefore they must be tested and evaluated based on the spectral responsivity of the average human eye. Radiometry covers all optical spectral regions, ranging from ultraviolet to infrared, while the photometry only the range of light that is visible for average human eye, that is, in the spectral range from 380 to $770 \mathrm{~nm}$. In the last times, human eye was used exclusively as an optical detector. To measure the intensity of a test light, the test light source was moved and placed at the varied distances from an eye or a screen and compared with the intensity of a standard light source positioned at a fixed position by a visual observation. The distance of the test light source was set so that both light sources, test and standard, appear equally bright. The estimated intensity of the test light source is calculated as the ratio of the intensity of the standard source and the ratio of the distances squared. Such a measured light intensity was named candle power, or in present terminology luminous intensity. This photometric quantity was the first defined photometric quantity. Since the 1940s the human eye, which was predominantly used as an optical detector, has been replaced by a light-sensitive detector (solid-state detector, photomultiplier tube).

Modern photometry measurements have been performed with the help of photodetectors, thus referring to the physical photometry. Physical photometry characterizes the optical radiation with an optical detector that mimics the spectral response of the human eye, that is, it has incorporated weighted spectral response same as the spectral response of a human eye. According to Table 2.1, the photometric units include the lumen or the luminous flux, the candela or the luminous intensity, the lux or the illuminance, and the candela per square meter or the luminance. Each photometric quantity is the spectrally integrated corresponding radiometric quantities weighted by the human eye spectral response.

## 电子代写|光纤代写Optical Fiber代考|SPECTRAL RESPONSE OF A HUMAN EYE

In 1924, the relative spectral response of the human eye was specified by the Commission Internationale de l’Eclairage (CIE), (the International Commission on Illumination). Such a defined relative spectral response of the human eye was called the spectral luminous efficiency for photopic vision with a joined symbol $V(\lambda)$. The relative spectral response is defined in the spectral domain ranging from 360 to $830 \mathrm{~nm}$ and it is normalized to its peak value at $555 \mathrm{~nm}$. The values were republished by CIE in 1983 and adopted by Comité International des Poids et Mesures (CIPM) (the International Committee on Weights and Measures) in the same year. Tabular presentation of the spectral luminous efficiency for photopic vision values at $5 \mathrm{~nm}$ increments is presented in Table 2.3. One can notice from the tabular values that outside the spectral range ranging from 380 to $770 \mathrm{~nm}$, the values of the spectral luminous efficiency for photopic vision are smaller than $10^{-4}$ thus negligible for the calculations.

A photometric quantity $X_{\mathrm{v}}$ can be related to the corresponding radiometric spectral quantity $X_\lambda$ in the following way:
$$X_{\mathrm{v}}=K_{\mathrm{m}} \int_{\lambda=360 \mathrm{~mm}}^{\lambda=830 \mathrm{~m}} X_\lambda V(\lambda) \mathrm{d} \lambda,$$
where $K_{\mathrm{m}}$ is the constant that relates photometric and radiometric quantities and it is named the maximum spectral luminous efficiency of radiation for photopic vision. The value of this constant is defined as the spectral luminous efficiency of radiation at the frequency of $540 \times 10^{-12} \mathrm{~Hz}$ (or at the wavelength of $555.016 \mathrm{~nm}$ in the standard air) to be $K_{\mathrm{m}}=683 \mathrm{~lm} / \mathrm{W}$. This value isn’t defined strictly for the wavelength of $555 \mathrm{~nm}$, where the peak value should appear, but for the wavelength that is slightly shifted from the maximum value. The exact maximum value of the constant $K_{\mathrm{m}}$ can be accurately calculated as $683 \mathrm{~lm} / \mathrm{W} \times V(\lambda=555 \mathrm{~nm}) / V(\lambda=555.016$ $\mathrm{nm})=683.002 \mathrm{~lm} / \mathrm{W}$, which can be simply rounded to $683 \mathrm{~lm} / \mathrm{W}$, with the negligible error.

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## 电子代写|光纤代写光纤代考|人眼的光谱响应

1924年，人眼的相对光谱响应由国际照明委员会(CIE)(国际照明委员会)规定。这种被定义的人眼的相对光谱响应称为光视的光谱发光效率，并用一个联合符号$V(\lambda)$表示。相对谱响应定义在360到$830 \mathrm{~nm}$的谱域内，并归一化到$555 \mathrm{~nm}$的峰值。这些数值在1983年由CIE重新发布，同年被Comité国际计量协会(CIPM)(国际度量衡委员会)采用。表2.3显示了在$5 \mathrm{~nm}$增量处的光视值的光谱发光效率。从表格中的值可以看出，在380到$770 \mathrm{~nm}$的光谱范围之外，光位视觉的光谱发光效率值小于$10^{-4}$，因此可以忽略不计。

$$X_{\mathrm{v}}=K_{\mathrm{m}} \int_{\lambda=360 \mathrm{~mm}}^{\lambda=830 \mathrm{~m}} X_\lambda V(\lambda) \mathrm{d} \lambda,$$

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。

Posted on Categories:Optical Fiber, 光纤, 电子代写

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The radiometric quantities measurements, such as radiant flux, irradiance, radiance, and intensity, are made with the help of a radiometer, that is, the instrument that measures the optical flux captured by its surface. Typically, the flux that impinges the detector surface generates an electrical signal, which is proportional to the captured flux. By calibration, it is possible to make a relation between the measured radiant flux and the corresponding electrical signal. It is important to notice that due to the relation between the radiant flux and certain geometrical parameters, it is possible to measure other radiometric quantities by involving appropriate adjustments of the measurement setup. For example, if the detector measures a certain radiant flux that is captured by the detector active surface, the irradiance or the flux density can be measured by dividing the measured flux by the active area of the detector surface. Of course, the measured irradiance is averaged over the area of the entrance aperture.

Exitance is similar to the irradiance but it is the property of the radiation source. However, it can be also determined by measuring the radiant flux that is captured by the detector. If the radiant flux is known, then, based on the geometry of the measurement setup, the exitance of the source can be determined if the distance from the source to the detector and the size of the source are known.

## 电子代写|光纤代写Optical Fiber代考|INTEGRATING SPHERE

An integrating sphere is an optical device that consists of a spherical shell in which inner walls are covered with a diffuse, white, and highly reflective coating. To be able to perform the measurements, there are small holes at the sphere for entrance and exit ports. The main function of an integrating sphere is to spatially integrate the radiant flux by a uniform scattering or diffusing effect that occurs at its inner walls. Light rays, which are incident at any point on the integrating sphere inner walls, are due to the multiple scatterings, distributed evenly to the all other points at the inner sphere surface. An integrating sphere is typically used with some light source and a detector for radiant flux measurement and it has become a standard instrument in optical radiometry and photometry. It has a unique function of the total flux measurement of any light source in a single measurement. Typical integrating sphere arrangement is presented in Figure $2.15$. The light, which radiant flux $\Phi_1$ is to be measured, enters the integrating sphere multiple scatterings at the inner highly reflective and diffusive walls, the multiple scatterings at the inner highly reflective and diffusive walls, the irradiance $E$.

.使用说明

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## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。