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# 电子代写|光纤代写Optical Fiber代考|CSCO205B PHOTOMULTIPLIER

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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。