Functional near-infrared spectroscopy (fNIRS) is a new and nondestructive detection technology that can effectively measure changes in cerebral hemoglobin concentration. The development of a high-performance wearable fNIRS system is of great significance for clinical diagnosis and daily life monitoring. This paper compares the components of different fNIRS systems. Firstly, the selection and arrangement of light source and photodetector in the system are analyzed and compared. Secondly, the methods of data acquisition, data preprocessing and data analysis are compared. Finally, the methods of improving the temporal resolution, spatial resolution and portability of the system are discussed. This article provides guidance for the reader in designing a high-performance fNIRS system.

Bimetallic materials combine the characteristics of two kinds of metal and exhibit superior properties, which is widely concerned in the field of material applications. Preparing high performance functional materials at low cost is the key to the promotion and application of bimetal. Using Cu30Mn70 alloy as precursor, gold coated nanoporous copper substrate (Au@NPC) was fabricated by free corrosion and subsequent chemical plating. In addition to limiting the oxidation of copper in air, the gold coating reduces the aperture distance between ligaments, increases the electromagnetic coupling effect between adjacent ligaments, and make Au@NPC have stronger local electromagnetic field enhancement characteristics, which is better than the surface enhanced Raman scattering characteristics of nanoporous copper. Gold-copper bimetallic materials can be used as surface Raman enhanced scattering substrates with excellent stability at low cost.

Intelligent miniaturized medical devices have attracted more and more attention in the medical industry. These products are mainly composed of some micro electronic components, in which the point line connection structure of the device core chip needs to be completed by high-precision welding. Therefore, the higher recognition accuracy of solder joint and welded core wire is required. Whether they can be accurate and effective identification directly affects the final quality of welding. In order to complete the recognition of solder joint and core wire in the welding process with high quality, this study mainly uses the method of electronic microscope instrument combined with host computer VS17 + OpenCV to complete the image processing, and recognizes the solder joint and core wire end of the collected image. The color and geometric features of solder joint and core wire end are taken as the analysis object. After preprocessing, the region of interest is highlighted through their respective feature analysis. The segmentation process of solder joint and core wire end is completed through specific color threshold selection method and contrast enhancement algorithm. The recognition accuracy error of measured solder joint and core wire end is required within 0.1 mm. The experimental results show that the proposed identification algorithm of printed circuit board (PCB) solder joint and core wire end can effectively identify the position of solder joint and core wire end in the image and display its pixel coordinate value. After data sorting and analysis, the identification accuracy error of this algorithm is controlled within the tolerable range.

Electronic endoscope is an important equipment in the modern medical instruments. With the increase of production, automatic welding of endoscope signal line has become an inevitable trend. A field programmable gate array (FPGA) image processing system for welding spot detection of endoscope lens module was designed to accurately and efficiently capture the welding spot coordinates of endoscope lens module. In the whole system, OV5640 is used as the image acquisition device to collect the image data of the target board. Image processing is carried out by Verilog HDL hardware description language for welding spot detection and defect discrimination algorithm. The hardware test results show that the system can collect the coordinates of solder joints in real time and detect the defects between solder joints. The maximum error of the collected coordinates is less than 0.1mm. the detection accuracy is high, and the real-time performance is high. The system has a wide application prospect.

In this paper, terahertz photoinduced force microscopy (THz PiFM) is designed and built, which realizes the near-field photoinduced force nanoscopic imaging measurement in the terahertz band for the first time. Based on the atomic force microscopy, the system uses the sensitive detection ability of the probe to the force, and realizes the terahertz near-field microscopic imaging without detector. The system detected the light field gradient force generated by the near-field dipole interaction between the probe and the sample. The near-field nanoscopic imaging characterization of monolayer MoS2 grains excited by visible light was carried out, and the mechanism of near-field optical signal enhancement at the grain edge was analyzed. The results show that THz PiFM has a highly sensitive detection capability for carriers in two-dimensional materials. Compared with the traditional terahertz near-field microscopy imaging technology, THz PiFM does not require terahertz detector, and is a new low-cost, high-performance terahertz near-field microscopy imaging technology, and can achieve superior spatial resolution and imaging signal-to-noise ratio.

The ideal perfect vortex beam is a special beam whose intensity distribution does not change with the change of the topological charge. Compared with ordinary vortex beam, it can greatly improve the application efficiency in particle manipulation and optical fiber transmission. In order to explore the free space propagation characteristics of the perfect vortex beam, this article uses Hank transformation to calculate and analyze the effects of the topological charge, the initial surface ring radius and the ring width on its diffraction characteristics in detail, it is found that the perfect vortex beam does not have the characteristic of non-diffraction, and the halo will broaden with the increase of the diffraction distance and gradually transform to the Bessel function. When the radius of the initial surface increases or the width of the ring decreases, the diffraction effect increases, and the effect of the ring width is greater than the ring radius. Compared with the previous two cases, the topological charge has less influence on the diffraction effect. The research in this paper is expected to provide a useful theoretical reference for the further application of the perfect vortex beam.

The environmental factors, such as light radiation, water vapor, and oxygen, induce the degradation of two-dimensional perovskites, and therefore its stability greatly limits the further development and marketization of this material. Taking advantage of the strong stability and hydrophobicity of fluoride, fluorophenylethylamine was introduced into the organic layer of two-dimensional perovskites, which could effectively improve the stability of two-dimensional perovskites, but the fluorescence efficiency was partly reduced. To solve this problem, polystyrene (PS), polymethylmethacrylate (PMMA) and cycloolefin polymer (COP) were employed to encapsulate the two-dimensional perovskite film. The photoluminescence intensity was improved by 2.2, 1.3 and 1.4 times, respectively. The light stability was improved by 3.3, 3.1 and 3.9 times, respectively. Furthermore the humidity stability was also verified. This study provides a new idea for the development of two-dimensional perovskite films in optoelectronic devices.

In recent years, optical imaging and detection technology has been increasingly used in the field of biomedicine, which has many excellent characteristics such as high detection sensitivity, good biological safety and non-invasiveness. The development of this technology benefits from the optical properties of fluorescent substances (such as dyes, fluorescent proteins) and the development of optical imaging devices. Compared with traditional downconversion optical imaging methods, upconversion optical imaging has anti-Stokes shift luminescence properties. The optical imaging method shows good application prospects in the field of biomedicine, and the imaging method can avoid some disadvantages of downconversion luminescence. For example, the use of near-infrared light excitation can increase the penetration depth of light into the tissue, avoid the autofluorescence of the organism, and cause less damage to the tissue. Because of the particularity of this imaging method, it is necessary to introduce and review its applications in the field of biomedicine, including imaging detection and disease treatment. This has guiding significance for the rational use of upconversion luminescence technology and the rational design of upconversion luminescence materials.

Small objects are easy to be lost and misjudged in the detection task because of their relatively low resolution in the image. Aiming at the problem that the detection accuracy of small-scale targets in the current target detection algorithm is much lower than that of other sizes, the feature enhancement of small-scale targets is integrated into the feature pyramid structure to avoid the lack of small-scale feature information. The feature enhancement ability of multi-scale feature fusion is used to enrich the feature information of small-scale target feature layer, so as to improve the accuracy of small-scale target detection. The improved feature pyramid structure is applied to YOLOv3 network. The experimental comparative study shows that the detection accuracy of small-scale targets can reach 0.179, which is 22.6% higher than the original network.

Terahertz dual-comb spectroscopy has become a powerful spectral measurement technology recently due to its high frequency resolution and high sensitivity. According to the sampling principles and methods of dual-comb spectroscopy in time domain and frequency domain, a terahertz spectroscopic system with tunable repetition frequency based on two femtosecond lasers is established in order to improve the detection performance of the spectroscopic system in this paper. By changing the repetition frequency of an optical frequency comb, the effect of repetition frequency difference on the terahertz dual-comb spectrum is analyzed systemically. The results show that the smaller the repetition frequency difference in the effective range, the higher the detected spectral quality. The detection performance of the terahertz dual-comb spectroscopy system is optimal when the repetition frequency difference is 10 Hz. These results provide a method to select the most suitable repetition frequency difference for terahertz dual-comb spectroscopy.

Raman spectroscopy is a fast and nondestructive method, which is widely used in many fields. The peak and peak area method cannot meet the needs of product development. The paper took oxygen, nitrogen and carbon dioxide as the research, the quantitative analysis of peak value, peak area method, Rayleigh scattering normalization, a gas component normalization and the whole gas component normalization method were carried out. The four methods were compared in four terms: the influence of integration time, the stability and repeatability of quantitative detection, and whether they were restricted by 100% volume fraction. It is found that other methods can improve the repeatability and stability of measurement compared with peak and peak area method. Each of the four methods has advantages and disadvantages. In the process of product development, different quantitative calculation methods should be selected according to the requirements.