Handheld Raman Spectrometer to Transmit Data via Wi-Fi

How a Handheld Raman Spectrometer to Transmit Data via Wi-Fi

author: Susan

2022-01-05

How a Handheld Raman Spectrometer to Transmit Data via Wi-Fi

Introduction
Indian scientist Raman first discovered that after light interacts with molecules, the wavelength of part of the light will change. By studying the scattered light with these wavelengths, information about the molecular structure can be obtained. This effect is named the Raman effect. The intensity of Raman scattering is very weak, only 10-6-10-12 times the intensity of the incident light. With the emergence of lasers in 1960, lasers replaced mercury lamps as the excitation source of Raman spectrometers, and Raman spectrometers have also entered a new era of development. In this experiment, a handheld Raman spectrum detection device principle machine is built on the basis of the existing laser module, circuit system module (equipped with Wi-Fi module), external optical path module and miniature spectrometer module to study Wi-Fi communication Technology in the application of handheld Raman spectrometers.
Figure 1 shows the schematic diagram of the system principle of the Raman spectrometer, which is composed of a laser, an external optical path system, a spectroscopic system, a photoelectric detection system, and a data processing system. The incident laser light emitted by the laser light source is focused on the sample through the external optical path system. At the same time, the external optical path system collects the Raman scattered light to the spectroscopic system. The spectroscopic system splits the Raman scattered light. The photoelectric detection system obtains the corresponding wavelength and light intensity signal. The Raman spectrum is obtained through the data processing system.

Fig. 1 Raman spectrometer system schematic

Experiment System
The handheld Raman spectroscopy detection device is composed of a laser module, a circuit system module, an external optical path module, a miniature spectrometer module, a display module and a power supply, which are integrated into a shell to achieve miniaturization. Figure 2 shows the software development of Optosky Raman SDK Schematic diagram of the 3D structure of the handheld Raman spectroscopy detection device.

Fig. 2 Schematic diagram of 3D structure of handheld Raman spectroscopy detection device

The laser uses the narrow linewidth laser module of Optosky ATR20202-785. Its line width is less than 0.08 nm, the stability is better than 0.2% in 2 hours, and the built-in TEC cooling module can realize stable narrow line width laser output.
Optosky ATP5020R is selected for the miniature spectrometer module, which uses a cross asymmetric CT light path structure. The system is simple in structure and small in size. It includes interference filters to eliminate second-order diffraction. It uses SMA905 optical fiber interface. The dynamic range is 10000:1 and the minimum integration time is 6. ms, while the signal-to-noise ratio is increased to 900:1, which is suitable for weak Raman signal detection.
The external optical path module is a Raman probe ATR20105 with a working distance of 6 mm and a clear aperture of 8 mm.
The selected circuit system module is the MYS-6ULX-IoT development board launched by Shenzhen Mill Technology Co., Ltd. This development board is an embedded single-chip microcomputer with the Cortex-A7 core as the core, equipped with a Wi-Fi module and a display screen.

Fig. 3 wlan0 gets the IP address

Test Results
The principle machine of a handheld Raman spectroscopy detection device was built, as shown in Figure 4. The principle machine was used to collect the Raman spectrum of methamphetamine. The methamphetamine sample was in the form of transparent crystals, provided by the Zhejiang Provincial Public Security Bureau, and was captured on the spot. The collected spectrum data is received by the network communication software and then sent to the spectrum analysis software.

Fig. 4 Physical map of each module of handheld Raman spectroscopy detection device
Due to the strong fluorescence phenomenon and certain noise interference, the characteristic peaks of the collected Raman spectrum are not easy to identify, so the least square smoothing method is used to perform background subtraction on the measured Raman spectrum, as shown in Figure 5. The upper green curve in the figure is the Raman spectrum curve before the background baseline is subtracted, and the lower blue curve is the Raman spectrum curve after the background baseline is subtracted.

Fig.5 Raman spectroscopy of methamphetamine samples before and after background subtraction

Conclusion
The Raman spectrum obtained by measuring methamphetamine samples is representative of 625 cm-1, 710 cm-1, 842 cm-1, 1005 cm-1 and 1213 cm-1, which can all be in the theoretical Raman spectrum of methamphetamine. Correspondence is found in 617 cm-1, 732 cm-1, 861 cm-1, 1005 cm-1 and 1213 cm-1. Due to the error of the calculation method and other impurities contained in the methamphetamine sample, some deviations are caused, but the characteristic peaks are basically the same, indicating that the built-up handheld Raman spectroscopy detection device is feasible, and it also indicates that the Wi-Fi communication technology is suitable for handheld pulling. The application in the Mann spectrometer is successful.
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