Application of the hottest micro high resolution o

2022-08-12
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Application of micro high-resolution optical fiber spectrometer in the field of plasma

Abstract plasma is the aggregation state of the fourth substance after gas, liquid and solid. The cleaning of experimental platforms and the cleaning of spray paint appearance, plasma physics is a booming emerging science. Its application fields include controlled thermonuclear fusion, space science, environmental science, microelectronics and information industry, material synthesis and processing, national defense and high-tech applications. At present, the simplest method to measure the characteristic spectrum of plasma is to use the miniature, high-resolution, multi-channel optical fiber spectrometer of avantes company in the Netherlands

1. Introduction

with the increase of temperature, general substances are represented as solids, liquids and gases, which are collectively referred to as the three states of substances. When the gas temperature rises further, many or even all of the molecules or atoms will dissociate into electrons and positive ions due to intense collisions. At this time, matter will enter a new state, that is, a state mainly composed of electrons and positive ions (or positively charged nuclei). This state of matter is called plasma, which can be called the fourth state of matter

at present, the instruments for directly measuring plasma are divided into two categories: one is to measure the density and temperature of plasma, and there are two methods: one is to calculate according to the current generated by charged particles falling on the sensor, such as Faraday cylinder, deceleration potential analyzer and ion trap to sort out and clean the collector accordingly, and the other is the probe, which is calculated by adding different voltages to the probe; The other is to measure the characteristic spectral lines of plasma (spectral method). Optical fibers are used to detect plasma signals, and data are collected and analyzed by spectrometers, such as the miniature, high-resolution, multi-channel optical fiber spectrometer of avantes company in the Netherlands. The following mainly introduces the measurement of plasma by spectroscopy

2. Experimental part

2.1 instrument principle

avaspec-2048ft fast touch spectrometer of avantes company in the Netherlands adopts symmetrical optical path design, and the incident focal length and dispersion focal length are 75mm; It includes optical fiber connector (standard SMA interface, and other types of interfaces can also be selected), collimator, diffraction grating, focusing lens and Sony ilx554b 2048 pixel linear array CCD detector. The wavelength range is nm, and the maximum resolution is 0.04nm. USB1.1 or USB2.0 interface, RS-232 interface and i/o digital/analog interface are provided for the interface

Figure 1 optical platform

Figure 2 avaspec-2048ft fast triggered spectrometer

2.2 functions and features

2.2.1 external trigger function

avaspec-2048ft fast triggered spectrometer can start sampling after only 1.3 s delay after receiving the external trigger signal; The spectrometer can also send a TTL signal to trigger the pulse laser, and the delay between the sampling start time and the laser pulse can be set in AvaSoft software (-42ns to 2.7 MS, step size 42 NS). The negative delay sampling time of -42 ns is very useful for measuring the pulse laser

These characteristics of avaspec-2048ft make it suitable for applications that require fast response and precise synchronization with external trigger signals (its time jitter is only ± 21 NS), such as product detection on conveyor belts. The characteristics of the output TTL signal can be used for laser-induced breakdown spectroscopy (LIBS) measurement or fluorescence measurement. These applications require the sampling after the laser pulse is emitted for a period of time

Figure 3 external trigger sequence diagram

2.2.2 historical channel function

avaspec-2048ft fast triggered spectrometer can simultaneously monitor the changes of up to 8 output parameters over time, such as user-defined functions, integrals, peaks (wavelength, relative intensity), etc. Functions can be written in visual basic code. The results of timing measurement can be stored, loaded or printed. Zoom and panoramic display functions can quickly enlarge the interested part of the timing measurement results to the full image display<1. Range selection of Jinan experimental machine/p>

2.2.3 independent measurement function

avaspec-2048ft fast triggered spectrometer can be configured to carry out independent measurement without using a computer

avaspec-2048 spectrometer on USB2 platform adds Bluetooth (-bt) communication and SDRAM card option of storing spectrum on board, which can realize long-distance measurement and transmission (greater than 300 meters) and long-time spectrum data storage

2.2.4 high resolution in a wide spectral range

for plasma measurement and LIBS measurement, the spectrometer is generally required to have a high resolution in a wide spectral range

avaspec-2048ft fast triggered spectrometer has a maximum resolution of 0.04nm, while the multi-channel spectrometer can meet the requirements in the nm spectral range, with a resolution better than 0.1nm. At the same time, optical fiber bundles are used for detection (one end is an optical fiber connector, which is used to detect signals; the other end is multiple connectors, which are connected to various channels). The operation is simple and can ensure the detection of signals at the same location

2.2.5 design of symmetrical optical path

the ratio of incident focal length and dispersion focal length of symmetrical optical path is strictly 1:1. The perfect linear image is formed on CCD, and the influence of stray light is minimized because there is no optical path intersection

2.2.6 synchronous data sampling between multiple channels

avaspec-2048ft fast triggered spectrometer can be configured into dual channels or multiple channels (up to 8 USB1.1 platforms and up to 128 USB2.0 platforms). It adopts master-slave circuit board control, and realizes synchronous data acquisition in a real sense between channels. Each channel includes an independent optical platform

Fig. 4 avaspec-2048ft-8-rm eight channel spectrometer

2.2.7 good temperature stability and small thermal drift

avaspec-2048 spectrometer adopts stress-free assembly between the optical elements and the base plate, which is processed by special processes before leaving the factory, so the environmental temperature has little impact on the spectrometer, and only 0.1 pixel will drift when the environmental temperature changes by 1 ℃; Excellent temperature stability ensures the accuracy and repeatability of long-term measurement

2.3 measurement method

in fact, the method of using avaspec-2048ft spectrometer to measure the characteristic spectral lines of plasma is very simple, as shown in Figure 5. Step 1: install AvaSoft full full software; Step 2: connect the optical fiber, spectrometer and computer, fix one end of the optical fiber and align it with the measured plasma, and then run the software; Step 3: the software will draw the collected data into a spectrogram

since the spectral intensity measured by the spectrometer is a relative value (electronic recording value, unit counts), if you want to measure the absolute intensity, you can choose to conduct absolute radiation calibration on the spectrometer in the calibration laboratory of avantes company in the Netherlands, with the wavelength range of nm. In order to make the whole measuring device more flexible, you can also buy a radiation calibration light source to calibrate on site

Figure 5 layout of plasma characteristic spectral line measurement experiment

2.4 test data and device

above is the spectrogram data of a plasma measured by avaspec-2048ft fast triggered spectrometer

Figure 6 is the actual device of avaspec-2048ft fast triggered spectrometer to measure the plasma of inert gas during discharge

3. typical applications and users

in China, the units and applications of avaspec-2048ft fast triggered spectrometer for plasma measurement are as follows:

1. Institute of plasma physics, Chinese Academy of Sciences, research based on Tokamak

2. Department of Engineering Physics, Tsinghua University, based on the research of low temperature plasma physics and material growth

3. School of chemistry and molecular engineering, Peking University, research on low temperature plasma synthesis based on nano materials

4. Institute of modern physics, Fudan University, plasma spectral measurement during gas discharge

5. Plasma propulsion laboratory of Harbin Institute of technology, based on the research of plasma propulsion measurement technology in outer space environment

6. Northwest Institute of nuclear technology, plasma research on gas high voltage discharge process

7. Plasma Physical Chemistry Laboratory of Dalian University of technology, research on the preparation of nano catalysts by plasma catalysis and plasma chemistry

8. PLA Institute of electronic engineering, research on solid combustion plasma and plasma stealth technology

9. School of physics, Suzhou University, research based on plasma deposition

10. School of materials, North China University, research based on arc plasma

11. Beijing Institute of fashion, research based on low temperature plasma modification technology

12. The plasma of Beijing Institute of printing has received strong support and high praise from the Department of raw materials of the Ministry of industry and information technology and relevant industry associations. The physics and materials research laboratory is based on the research of plasma deposition

13. Research based on laser-induced breakdown spectroscopy (LIBS) technology at Peking University, Beijing Institute of geology of nuclear industry, Northern Jiaotong University, South China University of technology, China University of Geosciences, Shanxi University, Zhejiang Normal University, etc

4. conclusion

using avaspec-2048ft fast triggered spectrometer for plasma measurement has the characteristics of high cost performance, high sensitivity, high measurement accuracy, fast measurement speed, simple operation, and small volume, which is convenient to be integrated into the system for measurement. (end)

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