Focusing field energy flow simulation of an azimuthally polarized Lorentz-Gaussian beam modulated by a concentric vortex phase mask.

Based on the vector diffraction theory, this paper investigated the energy flow evolution of focusing an azimuthally polarized Lorentz-Gaussian beam modulated by concentric vortex phase mask. Three concentric zones make up the concentric vortex phase mask: the center zone, middle circular zone, and outer circular zone. Each zone has an adjusted phase. The findings demonstrate that flexible transverse energy flow rings can be obtained in the focal plane and that transverse energy flows with various polygonal forms can be produced by varying the middle circular radius or phase distribution. By adjusting the phase of the center zone and outer circular zone, the normalized transverse energy flow distribution can be rotated or changed. Findings demonstrate that this technique offers a potent means of controlling the distribution and orientation of Poynting vectors and electromagnetic fields. Moreover, a series of energy flow rings are generated to facilitate the transportation of absorptive particles to predetermined positions. These phenomena may provide a new approach for particle capture and optical particle manipulation.

A Novel Deep Convolutional Neural Network Combining Global Feature Extraction and Detailed Feature Extraction for Bearing Compound Fault Diagnosis.

This study researched the application of a convolutional neural network (CNN) to a bearing compound fault diagnosis. The proposed idea lies in the ability of CNN to automatically extract fault features from complex raw signals. In our approach, to extract more effective features from a raw signal, a novel deep convolutional neural network combining global feature extraction with detailed feature extraction (GDDCNN) is proposed. First, wide and small kernel sizes are separately adopted in shallow and deep convolutional layers to extract global and detailed features. Then, the modified activation layer with a concatenated rectified linear unit (CReLU) is added following the shallow convolution layer to improve the utilization of shallow global features of the network. Finally, to acquire more robust features, another strategy involving the GMP layer is utilized, which replaces the traditional fully connected layer. The performance of the obtained diagnosis was validated on two bearing datasets. The results show that the accuracy of the compound fault diagnosis is over 98%. Compared with three other CNN-based methods, the proposed model demonstrates better stability.

Magnetization properties of radially polarized Bessel-Gaussian vortex beams with radial phase modulation in a 4π focusing system.

This paper explored the optically induced magnetization properties of radially polarized Bessel-Gaussian vortex beams with radial phase modulation in a 4π high numerical aperture (NA) focusing system, which is based on the vector diffraction theory and the inverse Faraday effect. The results show that in the case of radial modulation parameter L=0, one longitudinal magnetization chain with adjustable length can be obtained by modulating the truncation parameter ß. When the radial modulation parameter L=1.3, two magnetization chains can be obtained by modulating the truncation parameter ß. By modulating the radial modulation parameter L, two magnetization chains along the optical axis can be generated, each with four dark magnetic traps; meanwhile, the spacing between two magnetization chains can be adjusted. These results may be helpful in high-density all-optical magnetic recording, atom capture, and magnetic resonance microscopy.

Focusing characteristics of chirped phase-modulated Lorentz-Gaussian vortex beams.

This work presents a thorough investigation of the focusing characteristic of chirped phase modulated Lorentz-Gaussian (LG) vortex beams based on the vector diffraction theory. The results show that changing the first-order chirp parameter c 1 can effectively adjust the size of the focusing spot, and the distance between focusing spots can also be controlled. The second-order chirp parameter c 2 can control the up-and-down movement of the optical chain in the focusing region. Simultaneously, the length of the focusing spots can be accurately changed by modulating the waist width ω. In addition, the influence of integer topological charge number m on controlling the size of an optical dark trap is discussed in detail. And fractional topological charge number m can control the rotation of focus peak and the number of optical dark traps. Potential applications of these findings include optical shape and capture, optical particle transmission, and contemporary medical care.

Compact Fluorescence Spectrometer with Built-In In-Line Calibration: Application to Detect Dissolved Organic Matter in Water.

Fluorescence spectrometer (FS) is widely used for component analysis because each fluorescing material has its own characteristic spectrum. However, the spectral calibration is complicated and bulky. Herein, an in-line spectral calibration sheet (ISCS) was proposed in which a narrow band-pass filter and a linear variable filter (LVF) were integrated on a metal plate. By moving the ISCS, the transmitted excitation light power (TEP) as well as fluorescence spectrum can be seamlessly scanned, and the TEP can be used for in-line spectral calibration. A compact FS apparatus based on UV-LED excitation, metal capillary (MC) and ISCS was fabricated (i.e., ISCS-FS), and the ISCS-FS apparatus was applied to detect sodium humate in water. By employing TEP calibration, both the primary inner filter effect (PIFE) and the drift in the optical power of UV-LED can be simultaneously compensated. The linear correlation coefficient of signal concentration was improved from 0.89 to 0.998, and the relative standard deviation (RSD) of replicated detection was improved from 3 to 0.7%. A detection limit of concentration (DLC) of 1.3 µg/L was realized, which is 15-fold lower than that of a commercial FS apparatus (20 µg/L). The DLC is even comparable with that (0.5-4 µg/L) of commercial total organic carbon (TOC) analyzers, which are bulky and expensive. The linear correlation between the measurement results of ISCS-FS and commercial TOC analyzers can reach a good value of 0.94.

Photoelectric performance of InSe vdW semi-floating gate p-n junction transistor.

Semi-floating gate transistors based on vdW materials are often used in memory and programmable logic applications. In this paper, we propose a semi-floating gate photoelectric p-n junction transistor structure which is stacked by InSe/h-BN/Gr. By modulating gate voltage, InSe can be presented as N-type and P-type respectively on different substrates, and then combined into p-n junction. Moreover, InSe/h-BN/Gr device can be switched freely between N-type resistance and p-n junction. The resistance value of InSe resistor and the photoelectric properties of the p-n junction are also sensitively modulated by laser. Under dark conditions, the rectification ratio of p-n junction can be as high as 107. After laser modulation, the device has a response up to 1.154 × 104A W-1, a detection rate up to 5.238 × 1012Jones, an external quantum efficiency of 5.435 × 106%, and a noise equivalent power as low as 1.262 × 10-16W/Hz1/2. It lays a foundation for the development of high sensitivity and fast response rate tunable photoelectric p-n junction transistor.

Miniaturized integrating sphere light sources based on LEDs for radiance responsivity calibration of optical imaging microscopes.

LED-based integrating sphere light sources (LED-ISLSs) in the size of typical microscope slides were developed to calibrate the radiance responsivity of optical imaging microscopes. Each LED-ISLS consists of a miniaturized integrating sphere with a diameter of 4 mm, an LED chip integrated on a printed circuit board, and a thin circular aperture with a diameter of 1 mm as the exit port. The non-uniformity of the radiant exitance of the LED-ISLSs was evaluated to be 0.8%. The normal radiance of the LED-ISLSs in the range of (5∼69) W m-2 sr-1 was measured with a standard uncertainty of 1.3% using two precision apertures and a standard silicon photodetector whose spectral responsivity is traceable to an absolute cryogenic radiometer. The LED-ISLSs were applied to calibrate the radiance responsivity of a home-built optical imaging microscope with a standard uncertainty of 2.6∼2.9%. The LED-ISLSs offer a practical way to calibrate the radiance responsivity of various optical imaging microscopes for results comparison and information exchange.

A method for optimizing the reference temperature in the effective emissivity calculation of nonisothermal blackbody cavities.

For a nonisothermal blackbody cavity, different reference temperatures have influence on the calculation of effective emissivity. Previous studies proposed a weighted average method which can be indicated by a priori to calculate the reference temperature. However, these studies did not mention how to define the weight function but used some arbitrary temperature or the temperature of a fixed position like the central bottom of the cavity as the reference temperature. In this study, a quantitative analysis and calculation method, which is implemented in the Monte Carlo method based optical simulation software Tracepro, is proposed to define the weight coefficients and optimize the reference temperature. To do so, in the Tracepro software, a surface source is placed in front of the cavity opening and emits radiation to the blackbody cavity. The radiation from this surface source can be absorbed or reflected many times in the cavity, and finally the incident radiation distribution in the cavity can be obtained. According to the principle of light path reversibility, the normalized incident radiation can be considered as the contribution of its position to the effective emissivity. In the experiment, the actual temperatures of two different-shaped blackbody cavities are measured with the non-contact method in 873 K temperature. By dividing the inner surface of each blackbody cavity into several regions based on the positions of the actually measured temperature points, the incident radiation from the surface source to each segmented region is calculated and normalized to the total incident radiation across all regions as its weight coefficient; the reference temperature is the sum of the weighted temperature (by multiplying each weight coefficient with its measured temperature) in each region. Different from previous studies, this study optimizes the reference temperature by considering the contribution of the whole cavity to the effective emissivity, which should be more consistent with the actual situation. Moreover, the influences of different shapes of the blackbody cavities, different radiation characteristics of the inner surface materials and different viewing conditions of the effective emissivity on the reference temperature are discussed and compared. The results suggest that the optimization of reference temperature has close link with above factors and thus should be calculated individually.

Analysis and improvements of effective emissivities of nonisothermal blackbody cavities.

The emissivity of the blackbody is a very important parameter in spectral radiance measurement systems. In the conventional method, the emissivity is calculated based on the isothermal model. However, the actual temperature distribution in the blackbody cavity is always nonisothermal; the emissivity calculated based on the isothermal model may not accurately present the radiation characteristic of the blackbody. In this study, the actual temperature distributions of two blackbodies (one has an extended cone shape, and the other a 65-mm diameter cylindrical shape) are measured, and the emissivities are calculated accordingly based on the nonisothermal model at a certain temperature (873 K). The results show there are different tendencies of temperature distributions in the two blackbodies. When compared with the isothermal model, the emissivities in the 873 K temperature and 2.0-20.0 µm wavelength condition are about 1.75% and 0.18% lower at the nonisothermal model for the extended cone shape and cylindrical blackbodies, respectively. To improve the emissivity, different types of apertures are customized for the two blackbodies. For the extended cone-shaped blackbody, the emissivity in the 873 K temperature and 2.0-20.0 µm wavelength condition increases by 1.12% when using a ring-shaped graphite aperture in the cavity, whereas for the cylindrical-shaped blackbody, the emissivity in the same condition increases by 0.09% when using a high-reflective aperture in front of the cavity opening. Different from previous studies, this study provides new insight in calculating and improving the effective emissivity of blackbodies by using the measured temperature in the cavity based on the nonisothermal model.

Crystallinity and Sub-Band Gap Absorption of Femtosecond-Laser Hyperdoped Silicon Formed in Different N-Containing Gas Mixtures.

Femtosecond (fs)-laser hyperdoped silicon has aroused great interest for applications in infrared photodetectors due to its special properties. Crystallinity and optical absorption influenced by co-hyperdoped nitrogen in surface microstructured silicon, prepared by fs-laser irradiation in gas mixture of SF6/NF3 and SF6/N2 were investigated. In both gas mixtures, nitrogen and sulfur were incorporated at average concentrations above 1019 atoms/cm³ in the 20-400 nm surface layer. Different crystallinity and optical absorption properties were observed for samples microstructured in the two gas mixtures. For samples prepared in SF6/N2, crystallinity and light absorption properties were similar to samples formed in SF6. Significant differences were observed amongst samples formed in SF6/NF3, which possess higher crystallinity and strong sub-band gap absorption. The differing crystallinity and light absorption rates between the two types of nitrogen co-hyperdoped silicon were attributed to different nitrogen configurations in the doped layer. This was induced by fs-laser irradiating silicon in the two N-containing gas mixtures.

Methanol-Water-Dependent Structural Changes of Regenerated Silk Fibroin Probed Using Terahertz Spectroscopy.

The mechanism of ß-sheet crystallization in silk fibroin remains unclear, due to the incomplete information of protein assembly and structural state. The emerging terahertz (THz) spectroscopy (<10 THz) has been taken as an important tool to detect new aspects of biomolecular structure and is used for the first time to analyze the methanol-water (MeOH) induced structural changes of Bombyx mori silk fibroin. Mid-infrared spectroscopy (IR) and X-ray diffraction (XRD) results show that silk fibroin initially exists in a typical silk I form and reassemble into a predominant silk II (antiparallel ß-sheet crystal) structure after MeOH treatment. The samples treated with MeOH-H2O mixed solutions show a predominant silk I structure without any silk-II-related peaks. As the MeOH concentration approaches 40 vol%, the absorbance of the ß-sheet-related IR bands and the XRD peaks gradually increase, indicating a formation of ß-sheet crystal during this process. THz spectrum shows the absorption capacity below 3 THz as well as the absorbance at 5.1 THz and 7.9 THz is indeed affected by the MeOH-H2O treatment, implying a MeOH-H2O-dependent change of intermolecular H-bonds in silk fibroin. The THz spectrum for silk fibroin gives additional information to the existing studies on the MeOH-H2O induced ß-sheet crystallization of silk fibroin, which may help us understanding the structural changes of natural silk.

Ultrahigh infrared normal spectral emissivity of microstructured silicon coating Au film.

We studied infrared normal spectral emissivity on quasi-periodic microstructured silicon, which was prepared by femtosecond laser irradiation in SF6 ambient gas, coated with 100 nm thick Au thin film. The observed emissivity is higher than any reported previously for a flat material with a thickness of less than 0.5 mm, at a temperature range of 200 °C to 400 °C. The emissivity over the measured wavelength region increases with temperature and the spike height. These results show the potential to be used as a flat blackbody source or for applications in infrared thermal sensor, detector, and stealth military technology.

Strong infrared absorber: surface-microstructured Au film replicated from black silicon.

With quasi-periodic microstructures, great enhancement of infrared light absorption of Au film over a broad wavelength band (2.7~15.1 µm) was realized experimentally for the first time. The microstructured Au film was prepared by replica molding of the surface of femtosecond (fs) laser microstructured silicon (black silicon). This unique absorption characteristic is mainly ascribed to good impedance match from free space to Au film. The surface of the sample was examined by X-ray photoelectron spectroscopy (XPS) and the four peaks of absorptance were ascribed to residual polydimethylsiloxane (PDMS), H2SO4, adsorbed water and CO2 in the air, respectively.