Fiber optic temperature sensors for small-scale heat sources have an urgent need in many industrial fields, for example, the temperature field of the laser heat source, mini LED, microchip, and so on. To the best our knowledge, we first propose and demonstrate an ultrashort fiber optic temperature sensor based on a Fabry–Perot (FP) interferometer which combines a low reflection fiber Bragg grating (FBG) with Fresnel reflection (i.e., ~4%) on the fiber end face. This unique FBG exhibits a broad Gaussian spectrum with a full-width at half-maximum (FWHM) bandwidth of 12.4 nm. This FBG-FP cavity structure was fabricated by a femtosecond laser line-by-line (LbL) scanning technology, and it has stronger mechanical strength due to no damage to the fiber material compared to other fiber optic FP interferometers. The free spectrum range (FSR) of the FBG-FP cavity is about 1.56 nm, corresponding to the cavity length can be calculated to be about $530 \mu \text{m}$ . The selected dip wavelength of the FBG-FP cavity sensor changes linearly with the temperature increase, corresponding to the temperature sensitivity of 10.8 pm/°C. Moreover, the FBG-FP cavity sensor exhibits a high spatial resolution of $580 \mu \text{m}$ and it can be used to measure the temperature of the small-scale laser spot due to its compact structure. The experimental results show the temperatures at different positions of 1064 nm laser exposure area are 138.4 °C, 111.5 °C, and 74.4 °C, respectively.
Fiber optic temperature sensors for small-scale heat sources have an urgent need in many industrial fields. We first propose and demonstrate an ultra-short fiber optic temperature sensor based on a Fabry-Perot (FP) interferometer which combines a fiber Bragg grating (FBG) with Fresnel reflection on the fiber end face. The FBG with a grating length of 50 μm was inscribed by a femtosecond laser line-by-line scanning technology. This FBG exhibits a resonant wavelength of 1548.8 nm and a broad full width at half maximum (FWHM) bandwidth of 12.4 nm. The selected dip wavelength of the FBG-FP cavity sensor changes linearly with the temperature increase, corresponding to the temperature sensitivity of 10.8 pm/°C. Moreover, the FBG-FP cavity sensor can be used to measure the temperature of the small-scale laser spot due to its compact structure. The experimental results show the temperature at different positions of laser exposure area are 138.4 °C, 111.5 °C and 74.4 °C, respectively.
The article discusses the use of SERS and microfluidic technology to improve the reproducibility of SERS detection. The article focuses on the use of SPMF SERS probes, which provide a large interaction area and flexible integration with microfluidic chips. The SPMF SERS probe is prepared by depositing Au nanorods on a planar polished fiber surface, and is integrated into a microfluidic channel to form a glass-based microfluidic-SERS chip. The optimized residual thickness of 62 μm is determined by considering the evanescent wave intensity, transmission loss, and experimental feasibility. The optimized microfluidic-SERS chip shows low detection limits and good spectral reproducibility. The chip is further used to detect pesticide and antibiotic residues in tap water, with the detection limits of 10-9 M for thiram and 10-6 M for levofloxacin. This work provides an effective way to realize highly sensitive and reproducible SERS detection, with potential applications in environmental science and biomedicine.
Abstract Si 3 N 4 ceramic matrix composites (SN‐CMCs) have been designed and widely used in many engineering fields under externally loading conditions. It is well known that the wear of materials is closely related to components’ mechanical reliability and service life. Understanding of the friction and wear performances is very important to provide insights into how to improve the wear resistance of materials. Coefficient of friction and wear rate, in general, are the most critical parameters of tribological behavior of materials. In this paper, friction and wear performances of SN‐CMCs are reviewed from the perspectives of doped phase, layered structure design, and laser surface texturing. The article describes the change of friction and wear performances of SN‐CMCs sintered with different additive phases. Tribological behavior of SN‐CMCs with engineering designed layered structure is also analyzed from the aspects of surface coating and gradient structure. In addition, friction and wear performances of SN‐CMCs under different lubrication conditions are also discussed. As an ideal processing method for hard and brittle ceramic materials, laser surface texturing has been proved to be an effective way to improve the wear resistance of SN‐CMCs. Researches have shown that the better wear resistance can be obtained by combining laser surface texture with layered structure. At the end of paper, studies on friction and wear performances of SN‐CMCs are summarized and prospected.
The use of surface-enhanced Raman scattering (SERS) spectroscopy for the detection of substances in non-volatile systems, such as edible oil and biological cells, is an important issue in the fields of food safety and biomedicine. However, traditional dry-state SERS detection with planar SERS substrates is not suitable for highly sensitive and rapid SERS detection in non-volatile liquid-phase systems. In this paper, we take contaminant in edible oil as an example and propose an in situ SERS detection method for non-volatile complex liquid-phase systems with high-performance optical fiber SERS probes. Au-nanorod clusters are successfully prepared on optical fiber facet by a laboratory-developed laser-induced dynamic dip-coating method, and relatively high detection sensitivity (LOD of 2.4 × 10-6 mol/L for Sudan red and 3.6 × 10-7 mol/L for thiram in sunflower oil) and good reproducibility (RSD less than 10%) are achieved with a portable Raman spectrometer and short spectral integration time of 10 s even in complex edible oil systems. Additionally, the recovery rate experiment indicates the reliability and capability of this method for quantitative detection applications. This work provides a new insight for highly sensitive and rapid SERS detection in non-volatile liquid-phase systems with optical fiber SERS probes and may find important practical applications in food safety and biomedicine.
Monitoring chemical reaction processes is of great significance in the study of the reaction mechanisms, and the optimization or control of reaction conditions. In this work, we demonstrate a novel monitoring method of chemical reactions using fiber SERS probes. The high-performance fiber SERS probes are prepared by the laser-induced evaporation self-assembly method (LIESAM), where lots of Au-nanorod clusters are deposited on the fiber facet for providing large SERS enhancement factor and good hot electron catalytic property. The remote and in-situ monitoring of chemical reactions is achieved through simply dipping the probes into the reaction solution. Taking the classic reduction reaction from 4-nitrothiophenol (4-NTP) to 4-aminothiophenol (4-ATP) by sodium borohydride (NaBH4) as an example, the time-resolved SERS spectra collected by probes clearly reflect the reduction procedure of the disappearance of 4-NTP, the formation of intermediate product 4,4'-dimercaptoazobenzene (4,4'-DMAB) and the emergence of the final product 4-ATP. In addition, a new Raman peak at 1366 cm-1 is observed when the 4-NTP is reduced in an H2 atmosphere generated by the hydrolysis of NaBH4, corresponding the formation of a new intermediate product 4-nitrosothiophenol (TP*). Also, the monitoring of the oxidation reaction from 4-ATP to 4,4'-DMAB is demonstrated using fiber SERS probes. Considering that all the SERS spectra are acquired with a portable Raman spectrometer and the fiber has a very low transmission loss, this work provides a good platform for remote, on-site and in situ monitoring of chemical reactions in liquid environments, and thus finds important applications in scientific research and industrial scenarios.
A silica fiber surface-enhanced Raman scattering (SERS) probe provides a practical way for remote SERS detection of analytes, but it faces the major bottleneck that the relatively large Raman background of silica fiber itself greatly limits the remote detection sensitivity and distance. In this article, we developed a convolutional neural network (CNN)-based deep learning algorithm to effectively remove the Raman background of silica fiber itself and thus significantly improved the remote detection capability of the silica fiber SERS probes. The CNN model was constructed based on a U-Net architecture and instead of concatenating, the residual connection was adopted to fully leverage the features of both the shallow and deep layers. After training, this CNN model presented an excellent background removal capacity and thus improved the detection sensitivity by an order of magnitude compared with the conventional reference spectrum method (RSM). By combining the CNN algorithm and the highly sensitive fiber SERS probes fabricated by the laser-induced evaporation self-assembly method, a limit of detection (LOD) as low as 10-8 M for Rh6G solution was achieved with a long detection distance of 10 m. To the best of our knowledge, this is the first report of remote SERS detection at a 10-m scale with fiber SERS probes. As the proposed remote detection system with silica fiber SERS probes was very simple and low cost, this work may find important applications in hazardous detection, contaminant monitoring, and other remote spectroscopic detection in biomedicine and environmental sciences.
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