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In recent years, deep learning has been widely used in the field of Raman spectral classification. However, the majority of the training and test sets are generated by the same device (generally a portable Raman spectrometer), with little difference between them, and the trained model may not be directly applicable to other devices. In this study, we established a database of six cephalosporin Raman spectra and proposed a classification algorithm VGGNeXt for cephalosporin Raman spectra. VGGNeXt takes inspiration from ConvNeXt, borrows some tricks from Swin-T, and re-improves VGG. Training data were high-resolution spectra from a benchtop Raman spectrometer, and test data were low-resolution spectra from a portable Raman spectrometer. The impact of preprocessing and dataset size on algorithm accuracy was explored. The results show that our network outperforms other comparative algorithms in all cases. After preprocessing, the VGGNeXt model achieves 100% accuracy on both full and halved data sets, and 99.9% accuracy when there are only 10 data for each cephalosporin class. The results show that the experimental ideas and processing methods in this paper solve the problems of model transfer and instrument standardization to a certain extent, and the model has good robustness.

We proposed an effective approach to enlarge the slow light bandwidth and normalized-delay-bandwidth product in an optimized moiré lattice-based photonic crystal waveguide that exhibits intrinsic mid-band characteristics. A flatband corresponding to a nearly constant group index of 34 over a wide bandwidth of 82 nm centered at 1550 nm with near-zero group velocity dispersion was achieved. A large normalized-delay-bandwidth product of 0.5712 with a relative dispersion of 0.114%/µm was obtained, which is a significant improvement if compared with previous results. Our results indicate that the photonic moiré lattice waveguide could advance slow light applications.

Surface-enhanced Raman scattering (SERS), owing to its high sensitivity and rapid response, has been widely used in various fields. However, it is still a challenge to prepare SERS substrates with ...

Phase-insensitive amplifiers (PIAs), as a class of important quantum devices, have found significant applications in the subtle manipulation of multiple quantum correlation and multipartite quantum entanglement. Gain is a very important parameter for quantifying the performance of a PIA. Its absolute value can be defined as the ratio of the output light beam power to the input light beam power, while its estimation precision has not been extensively investigated yet. Therefore, in this work, we theoretically study the estimation precision from the vacuum two-mode squeezed state (TMSS), the estimation precision of the coherent state, and the bright TMSS scenario, which has the following two advantages: it has more probe photons than the vacuum TMSS and higher estimation precision than the coherent state. The advantage in terms of estimation precision of the bright TMSS compared with the coherent state is researched. We first simulate the effect of noise from another PIA with gain M on the estimation precision of the bright TMSS, and we find that a scheme in which the PIA is placed in the auxiliary light beam path is more robust than two other schemes. Then, a fictitious beam splitter with transmission T is used to simulate the noise effects of propagation loss and imperfect detection, and the results show that a scheme in which the fictitious beam splitter is placed before the original PIA in the probe light beam path is the most robust. Finally, optimal intensity difference measurement is confirmed to be an accessible experimental technique to saturate estimation precision of the bright TMSS. Therefore, our present study opens a new avenue for quantum metrology based on PIAs.

Modified near-ballistic uni-traveling-carrier photodiodes with improved overall performances were studied theoretically and experimentally. A bandwidth up to 0.2 THz with a 3 dB bandwidth of 136 GHz and large output power of 8.22 dBm (99 GHz) under the −2V bias voltage were obtained. The device exhibits good linearity in the photocurrent-optical power curve even at large input optical power, with a responsivity of 0.206 A/W. Physical explanations for the improved performances have been made in detail. The absorption layer and the collector layer were optimized to retain a high built-in electric field around the interface, which not only ensures the smoothness of the band structure but also facilitates the near-ballistic transmission of uni-traveling carriers. The obtained results may find potential applications in future high-speed optical communication chips and high-performance terahertz sources.

Early diagnosis of pathogenic bacteria and treatment are essential to prevent further infection. Photothermal therapy (PTT) is a promising sterilization method with advantages of minimal invasiveness and high efficiency. The effect of PTT depends on the performance of photothermal materials. Herein, Ti

Reconstruction of multiple objects from one hologram can be affected by the focus metric judgment of autofocusing. Various segmentation algorithms are applied to obtain a single object in the hologram. Each object is unambiguously reconstructed to acquire its focal position, which produces complicated calculations. Herein, Hough transform (HT)-based multi-object autofocusing compressive holography is presented. The sharpness of each reconstructed image is computed by using a focus metric such as entropy or variance. According to the characteristics of the object, the standard HT is further used for calibration to remove redundant extreme points. The compressive holographic imaging framework with a filter layer can eliminate the inherent noise in in-line reconstruction including cross talk noise of different depth layers, two-order noise, and twin image noise. The proposed method can effectively obtain 3D information on multiple objects and achieve noise elimination by only reconstructing from one hologram.

This paper proposes flat bands and quasi-bound states in the continuum (Q-BIC) in a moiré lattice. In addition to the inter-layer coupling and small rotation angle, we show that the inter-node coupling in a single-layer moiré lattice can be controlled to obtain moiré flat bands. Unlike any flat bands reported in lattices such as kagome, rhombus, Lieb, and stub, we show that the moiré lattice exhibits both singular and non-singular flat bands simultaneously. We investigate the flat band’s eigenmodes to confirm their flatness and assess their singularity. The robustness of the flat bands to variation of background permittivity ε b is studied. Moreover, by further engineering the inter-node distance, the moiré flat band states change to a quasi-bound state at a non-zero wave vector. The Q-BIC exhibit an ultra-high quality factor (Q-factor) of 2.7142 × 10 6 , ultra-low mode volume of 0.214318 µ m 3 , and very narrow linewidth centred at 350.54 THz. We demonstrate the capability of the Q-BIC for lasing and nanocavity applications. Our results show that a single-layer photonic moiré lattice provides a suitable platform to explore fundamental phenomena related to flat band systems.

This paper proposes a near-perfect absorption device based on a cross-shaped titanium nanostructure and a multilayered structure. The multilayered bottom structure consists of alternately SiO2 and Ti. The whole device is put on a TiN substrate. The coupling between cross-shaped titanium nanostructures, and that between the cross-shaped titanium nanostructure and bottom multilayer, can further enhance the absorption at some wavelength where most of the energy is reflected or passes through in the device with a single structure. According to the simulation results, the device presents a nearly perfect absorption in a wavelength range from 300 nm to 2000 nm. The average absorptance in the wavelength range from 500 nm to 1400 nm exceeds 96%. This paper also provides a new idea for realizing perfect absorption, which is extensively used in sensing, controllable thermal emission, solar energy harvesting solar thermo-photovoltaic devices, and optoelectronic metrology.

Surface-enhanced Raman spectroscopy is an alternative detection tool for monitoring food security. However, there is still a lack of a conclusion of SERS detection with respect to pesticides and real sample analysis, and the summary of intelligent algorithms in SERS is also a blank. In this review, a comprehensive report of pesticides detection using SERS technology is given. The SERS detection characteristics of different types of pesticides and the influence of substrate on inspection are discussed and compared by the typical ways of classification. The key points, including the progress in real sample analysis and Raman data processing methods with intelligent algorithm, are highlighted. Lastly, major challenges and future research trends of SERS analysis of pesticide residue are also addressed. SERS has been proven to be a powerful technique for rapid test of residue pesticides in complex food matrices, but there still is a tremendous development space for future research.

Surface-enhanced Raman spectroscopy is an alternative detection tool for monitoring food security. However, there is still a lack of a conclusion of SERS detection with respect to pesticides and real sample analysis, and the summary of intelligent algorithms in SERS is also a blank. In this review, a comprehensive report of pesticides detection using SERS technology is given. The SERS detection characteristics of different types of pesticides and the influence of substrate on inspection are discussed and compared by the typical ways of classification. The key points, including the progress in real sample analysis and Raman data processing methods with intelligent algorithm, are highlighted. Lastly, major challenges and future research trends of SERS analysis of pesticide residue are also addressed. SERS has been proven to be a powerful technique for rapid test of residue pesticides in complex food matrices, but there still is a tremendous development space for future research.

Recently, more and more attention has been given to a semiconductor oxide-based surface-enhanced Raman spectroscopy substrate for its great stability and biocompatibility. However, its poor SERS sensitivity limits the applications of semiconductor oxide SERS substrates. In this paper, we provide a facile reduction method to modulate oxygen vacancy concentrations in oxide SERS substrates. Using MoO2 as an example, the resonance coupling as well as charge transfer between the semiconductor oxide SERS substrate and the target molecules were promoted for the reason of artificial oxygen vacancy embodied in the Raman signals being improved. By using the TEM, SEM, and XPS measurements, we confirmed that we successfully prepared defective MoO2- x with a polycrystalline surface. MoO2- x modulated oxygen vacancy treated with 6 wt % Li shows a very high detection sensitivity of 10-8 M (4.79 ug/L) for R6G, and the intensity of the Raman signal was highly enhanced. Because of the existence of defective energy levels, resonance coupling, as well as charge transfer between semiconductor and molecules, was obviously promoted. More importantly, the method of modulating oxygen vacancy can be widely used in semiconductor oxide materials for its chemical enhancement capacity can be promoted by artificial oxygen vacancy.

The present study aims to detect human serum for the screening and staging of lung adenocarcinoma (LAC) based on Raman spectroscopy and multivariate analysis. The tests on 190 serum samples including 82 normal individuals (NI) and 108 LAC were performed through label-free surface-enhanced Raman spectroscopy (SERS). The silver nanorods (NRs) wrapped with Al2O3 layers were used as SERS substrate. The Raman spectra of NI and LAC were compared and classified based on orthogonal partial least squares discriminant analysis (OPLS-DA). The diagnostic results showed that the specificity and sensitivity can reach 97.6% and 98.1%, respectively, based on leave-one-patient-out cross validation. The area under the receiver operating characteristic curve is greater than 0.99, indicating excellent classification of the two groups. Besides, the staging of LAC in different stages was also achieved, with the overall screening accuracy in stage I, stage II and stage III/IV was 84.3%, 93.3%, and 86.5%, respectively. This study demonstrated the technique of combining serum SERS spectra with OPLS-DA is a potential tool for the screening and staging of lung disease.

In this paper, a transmissive color filter with an ultra-narrow full width at half of the maximum is proposed. Exploiting a material with a high index of refraction and an extremely low extinction coefficient in the visible range allows the quality factor of the filter to be improved. Three groups of GaP/SiO2 pairs are used to form a Distributed Brag reflector in a symmetrical Fabry-Pérot cavity. A band-pass filter which is composed of ZnS/SiO2 pairs is also introduced to further promote the purity of the transmissive spectrum. The investigation manifests that a series of tuned spectrum with an ultra-narrow full width at half of the maximum in the full visible range can be obtained by adjusting the thickness of the SiO2 interlayer. The full width at half of the maximum of the transmissive spectrum can reach 2.35 nm. Simultaneously, the transmissive efficiency in the full visible range can keep as high as 0.75. Our research provides a feasible and cost-effective way for realizing filters with ultra-narrowed linewidth.

Controllable synthesis of novel metal nanoparticles and effective capture of hotspots are of great significance for SERS (surface-enhanced Raman spectroscopy) detection. Therefore, in this paper, a green controllable synthesis method of gold nanoparticle was achieved via epigallocatechin gallate reduction. Different morphologies of gold nanoparticles were synthesized just by changing the solution pH values, and the growth kinetics of AuNPs (gold nanoparticles) were systematically studied. The synthetic AuNPs were put in a droplet to study dynamic variations of self-assembly SERS hotspots from the liquid sol state to the solid dry state. The addition of halogen ions in the droplet can controllably regulate the self-assembly three-dimensional hotspot model of gold nanoparticles in the evaporation process of a droplet, during which the most enhancement effect can be easily captured. The dynamically changing images of nanoparticles in the process were graphically described based on the internal interaction forces of a droplet. Two stronger areas in the changes of SERS intensity were achieved with a high concentration of halogen ions, while only one maximum intensity area was obtained with a low concentration of halogen ions added. This method can effectively avoid complex and unpredictable microenvironments of SERS substrates in the liquid drop, further improving the reproducibility of SERS detection as well as broadening it to biological applications.

High-speed fringe structured light projection system is one of the key technologies for real-time and efficient measurement of phase three-dimensional topography measurement system. Its function is to generate a modulated fringe pattern for three-dimensional measurement. Digital projectors based on DMD (Digital Mircomirror Device) have been widely used in three-dimensional projection fringe measurement systems due to their advantages such as high contrast, high brightness, high efficiency, and secondary development. This paper designs a high-efficiency and high-uniformity fringe projector illumination system based on DMD, with a light efficiency of 54%, a uniformity of 91.5%, and an illumination beam angle distribution of 10°–38°. The overall system size is 70 mm × 74 mm × 35 mm, which is applied to the phase three-dimensional topography measurement system, has important research significance and practical value.

To obtain 3D information of an object, the object must be measured. As a non-contact and active measurement method, structured light-based 3D measurement technology has a wide range of applications. The image quality of the projection lens determines whether the projection grating can be clearly projected on the detection object in the 3D measurement, which directly affects the detection effect. In this paper, a DMD projection imaging lens suitable for 3D measurement of structured light is designed. The effective focal length is 33.9 mm, F/# is 2.3, and the total length of the optical system is 120 mm. At a lens resolution of 93 lp/mm, the MTF values of all fields of view are greater than 0.5, the maximum distortion of the full field of view is less than 1%, the field curvature is less than 0.05 mm, and the imaging quality is good enough for 3D measurement.

Fe3O4 magnetic nanoparticles with a particle size of ∼ 250 nm were synthesized by the thermal solvent method, and then modified with polyethyleneimine (PEI) as the intermediate layer on the Fe3O4 surface to form ultra-thin polymer interlayer to replace the traditional carbon shell and silicon shell interlayer. The seeding of Fe3O4 magnetic particles was completed thanks to the strong positive charge of the amino group of PEI-adsorbed 3-5 nm colloidal gold on the surface of magnetic beads, and the addition of silver nitrate and reducing agent to the magnetic microsphere enabled the silver shell to be coated on the surface of the magnetic microspheres almost without affecting their magnetism. Moreover, the effects of the additive amount of colloidal gold, silver nitrate and ultrasonic time on the magnetic nanoparticles were systematically studied. Morphology and characterization analysis showed that the prepared Fe3O4@Ag magnetic nanoparticles (MNPs) had uniform particle size, good dispersibility, strong magnetic response, and powerful SERS performance. Furthermore, the SERS performance of the composite nanometer material was investigated by using 4-aminophenol and pesticide paraquat as active targets, with the molecular concentration down to 10-8 M and 10-10 M, respectively, confirming that the functional composite had a good SERS activity and Fe3O4 magnetic core.