A lightweight CNN for multi-source infrared ship detection from unmanned marine vehicles.

Infrared ship detection is of great significance due to its broad applicability in maritime surveillance, traffic safety and security. Multiple infrared sensors with different spectral sensitivity provide enhanced sensing capabilities, facilitating ship detection in complex environments. Nevertheless, current researches lack discussion and exploration of infrared imagers in different spectral ranges for marine objects detection. Furthermore, for unmanned marine vehicles (UMVs), e.g., unmanned surface vehicles (USVs) and unmanned ship (USs), detection and perception are usually performed in embedded devices with limited memory and computation resource, which makes traditional convolutional neural network (CNN)-based detection methods struggle to leverage their advantages. Aimed at the task of sea surface object detection on USVs, this paper provides lightweight CNNs with high inference speed that can be deployed on embedded devices. It also discusses the advantages and disadvantages of using different sensors in marine object detection, providing a reference for the perception and decision-making modules of USVs. The proposed method can detect ships in short-wave infrared (SWIR), long-wave infrared (LWIR) and fused images with high-performance and high-inference speed on an embedded device. Specifically, the backbone is built from bottleneck depth-separable convolution with residuals. Generating redundant feature maps by using cheap linear operation in neck and head networks. The learning and representation capacities of the network are promoted by introducing the channel and spatial attention, redesigning the sizes of anchor boxes. Comparative experiments are conducted on the infrared ship dataset that we have released which contains SWIR, LWIR and the fused images. The results indicate that the proposed method can achieve high accuracy but with fewer parameters, and the inference speed is nearly 60 frames per second (FPS) on an embedded device.

Highly sensitive frequency upconversion detection from 1 to 3 THz with OH1 crystal.

The wide applications of terahertz (THz) wave technology in the ∼1-3 THz range has resulted in a surge in the demand for the performance improvement of THz wave detection technique. In this study, a frequency tunable, highly sensitive frequency upconversion detection based on a 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile (OH1) crystal at room temperature is demonstrated. Moreover, to effectively increase the signal-to-noise ratio in the low frequency range, a beam isolation enhancer is proposed and its effect is verified. The minimum detectable THz pulse energy reaches about 100 aJ at 1.9 THz. The frequency tuning ranging from 1 to 3 THz. Sensitivity comparison with a 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal system shows that OH1 is a more suitable nonlinear crystal in the 1-2.4 THz range.

Registration method for infrared and visible image of sea surface vessels based on contour feature.

In this paper, a modified infrared and visible image registration method based on contour feature is proposed. Our method firstly extracts the feature contour and eliminates sparkling waves contour of the sea surface, determines the main direction of the contour based on the contour image, then uses the improved Scale Invariant Feature Transform (SIFT) method as the feature point to construct the descriptor, completes the registration of the two images. 30 sets of infrared and visible-band vessels images were selected for registration experiments. Compared with previous reports, the experimental results showed that the proportion of effective feature points detected by this method can reach 70%, and the average number of effective feature points detected by proposed method can reach 196 in visible band image and 279 in infrared image. The running time was 5.3599s, shortened by 25% compared with previous reports, and the average Root Mean Square Error (RMSE) value was 2.3566, smaller by 75% compared with previous reports. An effective registration method is provided, which can be used for infrared and visible image processing and comprehensive utilization of information in marine scenes.

Coupling effects of the sum-frequency process and difference-frequency process on upconversion terahertz-wave detection via a DAST crystal.

Frequency upconversion technology with good performance including high sensitivity, fast response, and room-temperature operation is a promising method for terahertz-wave detection. The sum-frequency conversion and difference-frequency conversion jointly affect the detection ability for upconversion detection using organic crystals as nonlinear media. The concurrence of both processes has been ignored in past studies, which results in discrepancies between theoretical simulations and experimental results. In this paper, four-wave interaction equations involving two nonlinear conversion processes are proposed, and the effect of the sum-frequency process is analyzed in upconversion terahertz-wave detection via a 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal. The ratio of the sum-frequency signal to the difference-frequency signal varies for different terahertz frequencies and crystal thicknesses. Experiments suggest that theoretical simulations are good at predicting physical processes. Under certain conditions, the detection efficiency can be improved by simultaneously utilizing the two signals. The total signal photon number is not sensitive to the crystal thickness. Furthermore, the theoretical exploration of terahertz single-photon detection provides a noteworthy reference for future experiments.

Modeling for extracavity-pumped terahertz parametric oscillators.

This paper presents a modeling method for extracavity-pumped terahertz parametric oscillators (TPO) based on stimulated polariton scattering, in which the pumping beam is from a different laser, and the Stokes beam oscillates in its cavity. After suitable approximations and assumptions, the average THz wave amplitude in the nonlinear crystal is expressed as a function of the fundamental and Stokes wave amplitudes. Then the rate equation for the Stokes wave is obtained based on the Stokes wave increment within a cavity roundtrip timescale. After solving the Stokes wave rate equation, the Stokes wave temporal evolution is considered as a known parameter, and the properties of the residual fundamental and terahertz waves are obtained by numerically solving the coupled wave equations. This modeling method is applied to an extracavity-pumped TPO based on MgO:LiNbO3 crystal. The simulation results are basically consistent with the experimental results. The main reasons causing the deviations of the simulation results from the experimental results are analyzed. To the best of our knowledge, this is the first time to perform the modeling for extracavity-pumped Q-switched TPOs.

Global burden of musculoskeletal disorders and attributable factors in 204 countries and territories: a secondary analysis of the Global Burden of Disease 2019 study.

OBJECTIVE: To evaluate the global burden of musculoskeletal (MSK) disorders, as well as the five common conditions, and their relevant risk factors from 1990 to 2019. DESIGN: Data from the Global Burden of Disease Study 2019 were used in this study. SETTING AND PARTICIPANTS: Individuals of all ages and genders from 204 countries and territories in 21 regions. MAIN OUTCOME MEASURES: The outcomes were the numbers and age-standardised rates (ASRs) of incident cases, deaths and disability-adjusted life-years (DALYs) of MSK disorders. The average annual percent changes (AAPCs) in the ASRs were calculated using joinpoint regression analysis to estimate the trends. RESULTS: There were 322.75 million incident cases, 117.54 thousand deaths and 150.08 million DALYs of MSK disorders in 2019. The age-standardised incidence rate and age-standardised DALY rate in 2019 (incidence: AAPC=-0.32, 95% CI -0.34 to -0.31; DALYs: AAPC=-0.05, 95% CI -0.06 to -0.04) were lower than those in 1990. However, the age-standardised death rate showed a stable trend (AAPC 0.05, 95% CI -0.05 to 0.15) from 1990 to 2019. The peak age of onset and DALYs of MSK disorders was 50-54 years in 2019. The burden of MSK disorders in females was much higher than that in males (1.29 times more incident cases, 2.24 times more deaths and 1.45 times more DALYs in females than in males). A significant negative correlation was observed between the AAPCs in the ASRs and the Sociodemographic Index (SDI) score. Occupational risk exhibited the highest contribution to MSK disorders, and tobacco use and high body mass index were also major risk factors. CONCLUSIONS: This study demonstrates that the burden of MSK disorders tends to be lower in high-SDI regions than in lower-SDI regions. Strengthening the effectiveness of preventive measures against occupational risks may reduce the burden of MSK disorders.

Continuous tuning of unidirectional emission wavelength by bending a notched-elliptical polymer microdisk.

An approach of continuously tunable unidirectional emission through bending a notched-elliptical polymer microdisk is proposed. The characteristics of the bending-dependent action are carefully analyzed, and the resonance wavelength for unidirectional emission can be tuned continuously through bending the device. Such a whispering-gallery-mode microresonator enables unidirectional emission with ultra-low divergence, of which the emission efficiency and Q factor are stabilized, demonstrating the whole structure is robust and relatively insensitive within a certain bending angle range. A maximum resonance wavelength shift of ∼100 nm and Q factor of 1500 can be achieved with the total size of the microdisk less than 10 µm. This kind of microresonator is promising for applications in multilevel integrated photonics circuits and may open the door to new functionalities of resonator devices, from sensing to optical amplification.

All-solid-state widely wavelength-tunable and high-efficiency Yb:YSr3(PO4)3 laser.

We demonstrate an all-solid-state widely wavelength-tunable Yb:YSr3(PO4)3 (Yb:YSP) laser with high efficiency. The free-running Yb:YSP laser oscillating at multiple wavelengths in the range of 1024-1054 nm is realized with different crystal lengths and output coupler transmittances. The maximum output power of 2.72 W is obtained under the absorption pump power of 7.30 W. The highest slope efficiency is 66.9%, using the crystal of 6.5-mm-length. Simultaneous dual-wavelength operation can be realized as well. Furthermore, the widely wavelength-tunable Yb:YSP laser with a range of more than 60 nm (from 1004 to 1066 nm) is achieved using a birefringent filter. The experimental results indicate that the Yb:YSP crystal can be a promising candidate for ultrafast lasers in the 1 µm region.

Multi-wavelength microresonator based on notched-elliptical polymer microdisks with unidirectional emission.

A three-dimensional notched-elliptical microdisk with a wavelength-size notch on the boundary is proposed as a multi-wavelength and unidirectional emission lasing source. The device contains multiple properly designed two-dimensional whispering gallery mode-based polymer notched microdisks with different dimensions for use as a multi-wavelength source. It can have a relatively high optical quality factor of 4000, unidirectional emission with low far-field divergence ∼4°, and the efficiency of emission is as high as 84.2%. The effect of the notch size on the far-field divergence is analyzed, and the multi-wavelength lasing performance is characterized, demonstrating that the resonator is robust and reliable. This work paves a unique but generic way for the design of compact multi-wavelength microlasers.

Miniature resonator sensor based on a hybrid plasmonic nanoring.

A miniature resonator sensor based on a hybrid plasmonic nanoring with a gold layer coated uniformly on the outer boundary is described and investigated. By using the Lumerical finite-difference-time-domain (FDTD) method, the optimized sizes of the plasmonic layer thickness and the central hole are given and insight into the dependence of spectral displacements, Q factors, sensitivity and detection limits on the ambient refractive index is presented. Simulation results reveal that the miniature resonator sensor featuring high sensitivity of 339.8 nm/RIU can be realized. The highest Q factor can reach ∼60,000 with this nanoring and the minimum detection limit is as low as 1.5 × 10-4 RIU. The effects on the resonance shifts and Q factors due to geometric shapes of the inner boundary of the nanoring are discussed as well. This miniature resonator sensor has good potential for highly sensitive ultracompact sensing applications.

Diffraction-limited real-time terahertz imaging by optical frequency up-conversion in a DAST crystal.

Real-time terahertz (THz) wave imaging has wide applications in areas such as security, industry, biology, medicine, pharmacy, and the arts. This report describes real-time room-temperature THz imaging by nonlinear optical frequency up-conversion in an organic 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate (DAST) crystal, with high resolution reaching the diffraction limit. THz-wave images were converted to the near infrared region and then captured using an InGaAs camera in a tandem imaging system. The resolution of the imaging system was analyzed. Diffraction and interference of THz wave were observed in the experiments. Videos are supplied to show the interference pattern variation that occurs with sample moving and tilting.

10 aJ-level sensing of nanosecond pulse below 10 THz by frequency upconversion detection via DAST crystal: more than a 4 K bolometer.

By using frequency upconversion detection of terahertz (THz) waves via 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal with an optimized frequency conversion process, ultrahigh sensitivity has been achieved. Direct comparisons with a 4 K bolometer were implemented. By using a simple positive intrinsic negative (PIN) diode without either electrical amplification or optical amplification, frequency upconversion detection can compete with the commercial 4 K bolometer, while by replacing the PIN diode with an avalanche photo diode (APD), it performs more than three orders better than the 4 K bolometer. Based on power calibration, the minimum detectable THz pulse energy is in the order of 10 aJ (9-25 aJ) at 4.3 THz, with a pulse duration of 6 ns. Thus, the minimum number of THz photons that can be detected is down to the order of 10(3) at room temperature. The current THz detection system gives a noise equivalent power (NEP) in the order of 100 fW/Hz(1/2) (50-128 fW/Hz(1/2)). Moreover, by switching current optical detectors, the dynamic range is over six orders.

Broadband terahertz wave generation from a MgO:LiNbO3 ridge waveguide pumped by a 1.5 µm femtosecond fiber laser.

Cherenkov phase-matched terahertz (THz) wave generation from a MgO:LiNbO3 ridge waveguide was studied using optical rectification. Pumping was achieved using 20 and 60 fs laser pulses from a fiber laser centered at 1.56 µm. Time-domain spectroscopy (TDS) results showed a single-cycle pulse with 20 fs pulse pumping and a near-single-cycle pulse with 60 fs pulse pumping. The spectrum covered the range of 0.1-7 THz, with a signal-to-noise ratio of over 50 dB. The output power measured by a Si bolometer and a deuterated triglycine sulfate pyroelectric detector is shown and compared to that of a commercial photoconductive antenna. This system is believed to be a promising THz source for low-cost, compact, robust, and highly integrated TDS, THz imaging, and tomography systems.

Study of probe-sample distance for biomedical spectra measurement.

BACKGROUND: Fiber-based optical spectroscopy has been widely used for biomedical applications. However, the effect of probe-sample distance on the collection efficiency has not been well investigated. METHOD: In this paper, we presented a theoretical model to maximize the illumination and collection efficiency in designing fiber optic probes for biomedical spectra measurement. This model was in general applicable to probes with single or multiple fibers at an arbitrary incident angle. In order to demonstrate the theory, a fluorescence spectrometer was used to measure the fluorescence of human finger skin at various probe-sample distances. The fluorescence spectrum and the total fluorescence intensity were recorded. RESULTS: The theoretical results show that for single fiber probes, contact measurement always provides the best results. While for multi-fiber probes, there is an optimal probe distance. When a 400- µm excitation fiber is used to deliver the light to the skin and another six 400- µm fibers surrounding the excitation fiber are used to collect the fluorescence signal, the experimental results show that human finger skin has very strong fluorescence between 475 nm and 700 nm under 450 nm excitation. The fluorescence intensity is heavily dependent on the probe-sample distance and there is an optimal probe distance. CONCLUSIONS: We investigated a number of probe-sample configurations and found that contact measurement could be the primary choice for single-fiber probes, but was very inefficient for multi-fiber probes. There was an optimal probe-sample distance for multi-fiber probes. By carefully choosing the probe-sample distance, the collection efficiency could be enhanced by 5-10 times. Our experiments demonstrated that the experimental results of the probe-sample distance dependence of collection efficiency in multi-fiber probes were in general agreement with our theory.

Theoretical and experimental study on the Nd:YAG/BaWO4/KTP yellow laser generating 8.3 W output power.

A diode-side-pumped actively Q-switched intracavity frequency-doubled Nd:YAG/BaWO(4)/KTP Raman laser is studied experimentally and theoretically. Rate equations are used to analyze the Q-switched yellow laser by considering the transversal distributions of the intracavity photon density and the inversion population density. An 8.3 W 590 nm laser is obtained with a 125.8 W 808 nm pump power and a 15 kHz pulse repetition frequency. The corresponding optical conversion efficiency from diode laser to yellow laser is 6.57%, much higher than that of the former reported side-pumped yellow laser. The output powers with respect to the incident pump power are in agreement with the theoretical results on the whole.

Self-frequency-doubled KTiOAsO4 Raman laser emitting at 573 nm.

A self-frequency-doubled KTiOAsO4 (KTA) Raman laser is realized in a diode-end-pumped acousto-optically Q-switched intracavity Raman laser configuration. A 30-mm-long x-cut KTA crystal is used as the Raman medium, and its 671 cm(-1) Raman mode is employed to finish the conversion from 1064 nm fundamental laser to 1146 nm Raman laser. Self-frequency doubling of the Raman laser is accomplished in the same KTA crystal, and a 573 nm yellow laser is obtained. With an incident diode power of 10.9 W and a pulse repetition rate of 20.8 kHz, a yellow-laser power of 0.82 W is obtained. The conversion efficiency from diode power to yellow-laser power is 7.5%.

Efficient diode-end-pumped actively Q-switched Nd:YAG/SrWO4/KTP yellow laser.

An efficient intracavity frequency-doubled Raman laser was obtained by using an SrWO(4) Raman medium, an Nd:YAG ceramic gain medium, and a KTP frequency-doubling medium. Three laser cavities, including a two-mirror cavity, a three-mirror coupled cavity, and a folded cavity, were investigated. With the coupled cavity, a 2.93 W, 590 nm laser was obtained at an incident pump power of 16.2 W and a pulse repetition frequency of 20 kHz; the corresponding conversion efficiency was 18.1%. The highest conversion efficiency of 19.2% was obtained at an incident pump power of 14.1 W and a pulse repetition frequency of 15 kHz. The obtained maximum output power and conversion efficiency were much higher than the results previously obtained with intracavity frequency-doubled solid-state Raman lasers.

Coexistent optical parametric oscillation and stimulated Raman scattering in KTiOAsO4.

Coexistent optical parametric oscillation (OPO) and stimulated Raman scattering (SRS) are demonstrated in an X-cut KTiOAsO(4) (KTA) crystal. The 30-mm-long KTA crystal is placed within a diode-end-pumped acousto-optically (AO) Q-switched Nd:YAG laser cavity to construct an intracavity optical parametric oscillator. Coexistent Raman conversion of the fundamental wave is observed from the KTA crystal. With a diode power of 7.43 W and a pulse repetition rate (PRR) of 20 kHz, a signal (1535.0 nm) power of 0.92 W is obtained, corresponding to a diode-tosignal conversion efficiency of 12.4%. A first-Stokes (1091.4 nm) power of 0.17 W is obtained.

Theoretical and experimental research on the multi-frequency Raman converter with KGd(WO4)2 crystal.

An efficient multi-frequency extracavity Raman laser for nanosecond pulses was realized by taking advantage of the anisotropic optical property of the KGd(WO4)2 crystal. The conversion efficiencies of the converter were investigated versus the pump pulse energy, pump polarization, and output coupling rate experimentally and theoretically. Based on the coupled radiation transfer equations, a theoretical model was deduced to predict the performance of solid-state extracavity Raman lasers. This model was solved numerically to analyze the operation of the extracavity Raman laser with the KGd(WO4)2 crystal, and the numerical results had a good agreement with the experimental ones.

[Molecular analysis of hantavirus isolated from Shandong province].

OBJECTIVE: To compare the molecular characteristics of hantaviruses isolated from Shandong province by using PCR typing and nucleotide sequencing. METHODS: Total cellular RNA was extracted from hantaviruses infected Vero E6 cells, viral cDNA was amplified by polymerase chain reaction. PCR products of partial M Segments of 4 strains of hantaviruses were sequenced. Cross neutralization tests were performed. RESULTS: Four strains of hantavirus isolated from Rottus in Shandong province were SEO like viruses. The homology between Shandong isolates and other SEO like viruses was high at both amino acid and nucleotide levels. The homology among those 4 strains of hantaviruses was 98%. CONCLUSIONS: The SEO like hantaviruses were more conserved than other hantaviruses. The homology of SEO like hantaviruses isolated from Shandong province was as high as 98% at nucleotides level, though they were isolated at more than 10-year intervals.