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A novel demodulation scheme for a point-type fiber sensor is designed for salinity concentration monitoring based on a Sagnac interferometer (SI) composed of a tapered polarization-maintaining fiber (TPMF) and optical time stretching technology. The SI, constructed using a PMF with a taper region of 5.92 µm and an overall length of 30 cm, demonstrated a notable enhancement in the evanescent field, which intensifies the interaction between the light field and external salinity. This enhancement allows for a direct assessment of salinity concentration changes by analyzing the variations in the SI reflection spectra and the experimental results indicate that the sensitivity of the sensor is 0.151 nm/‱. In contrast to traditional fiber optic sensors that depend on spectral demodulation with slower response rates, this work introduces a new approach where the spectral shift is translated to the time domain, utilizing a dispersion compensation fiber (DCF) with the demodulation rate reaching up to 50 MHz. The experimental outcomes reveal that the sensor exhibits a sensitivity of -0.15 ns/‱ in the time domain. The designed sensor is anticipated to play a pivotal role in remote, real-time monitoring of ocean salinity.

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Lockdown due to the novel coronavirus disease 2019 (COVID-19) pandemic offers a unique opportunity to study the factors governing the variation in air pollution. A number of studies have investigated the cause underlying the occurrence of heavy haze pollution around the world during the lockdown period. However, information about spatiotemporal variations in gaseous pollutants and detailed quantifications of potential meteorological (METRO) impacts are limited. Ground measurements show that carbon monoxide (CO) pollution deteriorated in northern China despite strict control of human and industrial activities during the lockdown period in early 2020. In this study, a four-dimensional decomposition model was used to quantitatively extract the METRO impacts on the CO pollution over China. The results show that weakened winds elevated CO concentrations near Beijing and in northeastern China. Increased temperatures slightly elevated CO concentrations in northern and eastern China but reduced CO concentrations in northwestern China. Remarkable amounts of CO increases in northern China (e.g., by 0.21 mg/m3 within Beijing) were explained by anomalously high humidity, which could be associated with an enhanced interaction between aerosol and the boundary layer. After excluding the METRO impacts, the CO concentrations drastically declined across China (e.g., by 0.22 mg/m3 within Beijing), indicating that the lockdown indeed greatly lessened CO concentrations. However, the adverse METRO conditions counteracted the beneficial outcomes of emission reductions, leading to a deterioration of the CO pollution in northern China. These results indicate that the METRO factors can play a critical role in worsening air pollution despite a strict control of anthropogenic emissions.

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Colorectal carcinoma (CRC) has high mortality and increased incidence rates. An early detection of CRC is very important. Multiphoton microscopy (MPM) with high resolution and high sensitivity is used to effectively distinguish the microstructure changes of normal and mucinous adenocarcinoma slices of ex vivo human colonic tissues. In mucinous adenocarcinoma mucosa, the glands are distorted and elongated, the gland cavity is indistinct, and the mesh collagen fibers are diminished. In the submucosa, the collagens are seriously disordered, elongated, pushed aside, and sparsely visible, the content of elastic fibers is also broken and almost disappearing. Many cancer cells, some in cavity-like shape full of mucus surrounded by some collagen fibers, occupied the submucosa, which are comparable to hematoxylin-eosin (HE) stained images. Second harmonic generation and two-photon excitation fluorescence (SHG/TPEF) intensity ratio can be used further to quantitatively evaluate normality and abnormality. The fast Fourier transform (FFT) images show that the normal collagen fibrils are dense and in random order, and the cancerous collagen is certainly organized. The exploratory results show that it has potential for the development of multiphoton mini-endoscopy in real-time early diagnosis of CRC.

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Mouse is an important animal model to investigate skin physiological and pathological states. In this article, multiphoton microscopic imaging of in vivo hair mouse skin based on two-photon excited fluorescence and second harmonic generation was examined. Our results show that multiphoton microscopy can clearly display microstructure of stratum corneum, stratum spinosum, and dermis of in vivo mouse skin. The main components of epidermis and dermis such as corneocytes, spinosum cell, collagen fibers, and hair follicles can be distinctly identified in MPM images. Using the optional HRZ 200 fine focusing stage, thickness of different layers can be easily assessed. The results demonstrate that MPM can be regarded as an efficient method for in vivo investigation of skin physiological and pathological states by using hair mouse animal model.

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