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Starch pearls are widely used in bubble tea and desserts, yet the mechanistic understanding of the formation process of their textural properties remain unclear. To investigate the relationship between the multi-scale structure of starch and the textural properties of starch pearls, analyses of fine structure, crystal structure, rheological behavior, and textural profiling were conducted. The results showed that starch gels with a higher content of short-chain amylose (100 < X ≤ 1000) exhibited weaker formability during starch pearl preparation, leading to a lower flow behavior index (n*). This, in turn, positively influenced the hardness and resilience of the starch pearls. Cassava, potato, and yam starch pearls contained a large amount of long-chain amylopectin (24 < X ≤ 100) and long-chain amylose (5000 < X ≤ 20,000). The high proportion of long chains resulted in a weaker ordered structure, leading to increased peak viscosities and final viscosities and a higher consistency coefficient (k*). This structural feature enhanced the formability stability, viscosity, and chewability of starch pearls. Our findings reveal that variations in starch multi-scale structure significantly influence the textural quality and formability of starch pearls, providing valuable insights for optimizing starch selection and processing techniques in the food industry., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Terahertz (THz) radiation is widely recognized as a non-destructive, label-free, and highly- sensitive tool for biomedical detections. Nevertheless, its application in precision biomedical fields faces challenges due to poor spatial resolution caused by intrinsically long wavelength characteristics. THz scanning near-field optical microscopy (THz-SNOM), which surpasses the Rayleigh criterion, offers micrometer and nanometer-scale spatial resolution, making it possible to perform precise bioinspection with THz imaging. THz-SNOM is attracting considerable attention for its potential in advanced biomedical research and diagnosis. Currently, its family typically includes four members based on distinct principles, which are suitable for different biological applications. This review provides an overview of the principles of these THz-SNOM modalities, outlines their various applications, identifies the obstacles hindering their performance, and envisions their future development., Competing Interests: Declaration of competing interest The authors declare no competing interest., (Copyright © 2024. Published by Elsevier Inc.)

This work presents TTFDNet, a transformer-based and transfer learning network for end-to-end depth estimation from single-frame fringe patterns in fringe projection profilometry. TTFDNet features a precise contour and coarse depth (PCCD) pre-processor, a global multi-dimensional fusion (GMDF) module and a progressive depth extractor (PDE). It utilizes transfer learning through fringe structure consistency evaluation (FSCE) to leverage the transformer's benefits even on a small dataset. Tested on 208 scenes, the model achieved a mean absolute error (MAE) of 0.00372 mm, outperforming Unet (0.03458 mm) models, PDE (0.01063 mm) and PCTNet (0.00518 mm). It demonstrated precise measurement capabilities with deviations of ~90 μm for a 25.4 mm radius ball and ~6 μm for a 20 mm thick metal part. Additionally, TTFDNet showed excellent generalization and robustness in dynamic reconstruction and varied imaging conditions, making it appropriate for practical applications in manufacturing, automation and computer vision.

Vortex beams, known as a typical form of structured light, possess numerous applications in various fields. Their widespread application prospects have then sparked an in-depth analysis of the generation and manipulation of vortex modes in an active cavity, as well as the development of high-performance vortex lasers. In this paper, we report on a new class of highly efficient and high-power Nd:YAG vortex lasers in a robust and compact configuration, which allows direct generation of vortex beams with an easily controllable topological charge both in the continuous-wave and pulsed operation regimes. The on-demand generation of intracavity vortex modes is realized based on a Q-plate by controlling the geometric phase inside the laser resonator. The maximum output power in the continuous-wave regime is 4.11 W with a slope efficiency of 37.9%. Besides, the vortex pulses are also achieved by including a Cr:YAG crystal in the cavity as a saturable absorber. The shortest pulse width is 142.8 ns at a pulse repetition rate of 232.6 kHz, with a maximum average output power of 1.05 W. Vortex modes with other topological charges can be obtained by simply changing the corresponding Q-plate without sacrificing the lasing efficiency. The experimental results can shed some light on the design and building of highly efficient and high-power vortex lasers together with a well-defined controllable topological charge, aiming at some specific applications.

Traditionally, manipulation of spatiotemporal coupling (STC) of the ultrafast light fields can be actualized in the space-spectrum domain with some 4-f pulse shapers, which suffers usually from some limitations, such as spectral/pixel resolution and information crosstalk associated with the 4-f pulse shapers. This work introduces a novel mechanism for direct space-time manipulation of ultrafast light fields to overcome the limitations. This mechanism combines a space-dependent time delay with some spatial geometrical transformations, which has been experimentally proved by generating a high-quality STC light field, called light spring (LS). The LS, owing a broad topological charge bandwidth of 11.5 and a tunable central topological charge from 2 to -11, can propagate with a stable spatiotemporal intensity structure from near to far fields. This achievement implies the mechanism provides an efficient way to generate complex STC light fields, such as LS with potential applications in information encryption, optical communication, and laser-plasma acceleration., (© 2024. The Author(s).)

To solve the problems of untimely and low accuracy of tunnel project collapse risk prediction, this study proposes a method of multi-source information fusion. The method uses the PSO-SVM model to predict the surrounding rock displacement. With the prediction index as the benchmark, the Cloud Model (CM) is used to calculate the basic probability assignment value. At the same time, the improved D-S theory is used to fuse the monitoring data, the advanced geological forecast, and the tripartite information indicators of site inspection patrol. This method is applied to the risk assessment of Jinzhupa Tunnel, and the decision-makers adjust the risk factors in time according to the prediction level. In the end, the tunnel did not collapse on a large scale., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors. Published by Elsevier Ltd.)

The paper presents the results of multiplying the repetition frequency of the seed source to 396 MHz using an extra-cavity fiber multiplication method. The single crystal fiber rod-type amplifier was able to boost the average output power to approximately 15.9 W. Using a transmission gratings-based pulse compressor, an average output power of 9.56 W was achieved, corresponding to a burst energy of up to 382 µJ and a compression efficiency of 81.7%. The shortest pulse duration was optimized to be 594 fs; however, an obvious pedestal was also observed. This system reduces the impact of nonlinear effects on the device by increasing the repetition frequency, thereby increasing the injection energy of a single process in industrial processing.

Dirac points (DPs) and Weyl points (WPs) have received much attention in photonic crystals (PhCs) and three-dimensional (3D) metamaterials research due to the robust surface states and Fermi arcs. In this work, two pairs of triply degenerate points (TDPs) have been proposed in a 3D metamaterial by breaking the time reversal symmetry ( T ) with an external magnetic field. Based on these TDPs, two pairs of asymmetric surface states with spin-polarization are revealed, and a topological chiral beam splitter is demonstrated showing the different propagating directions of the right-handed polarization (RCP) and left-handed polarization (LCP) lights. Remarkably, we can achieve unidirectional propagation with RCP or LCP even excited by a linear source owing to the asymmetry surface state. Our work provides a new, to the best of our knowledge, platform to study spin-polarization surface states and the enhanced spin photonic Hall effect in the metamaterials.

In the process of cyclic blasting during tunnel excavation, the reserved surrounding rock sustains irreparable damage accumulation. For safe tunnel construction, it is imperative to understand the characteristics of blasting dynamic cumulative rock damage. Sonic wave test and numerical simulation methods were applied to the research. The JH-2 model was adopted as the damage model of surrounding rock. Based on the data transfer method between solvers in ABAQUS software, the cumulative damage was calculated. The damage characteristics were obtained by combining the sonic wave test results. According to the research findings, the entire reserved surrounding rock has periodic damage characteristics. Each periodic damage area has a funnel shape along the tunnel's longitudinal direction, with a length of 160 cm, and 1.07 times the excavation footage. The latter excavation footage's blasting effect on the damaged area of the previous footage rock is 40 cm long, with three cumulative damage patterns. The three cumulative damage patterns more clearly reveal the surrounding rock's additional damage law, the degree of additional damage is greatest with the distance of 5-20 cm from the latter excavation footage. The research can provide appropriate theoretical guidance for the design of the step-blasting construction tunnel's blasting scheme and lining., (© 2023. The Author(s).)

Numerical simulation based on SPH method, compared with laboratory experiments, using the grey correlation theory to analyze the correlation between the parameters of the elliptical bipolar linear shaped charge and the performance of the shaped charge jet. The structure of shaped charge is optimized by machine learning to obtain the optimal structural parameters, and it is compared with the rock crack development of shaped charge blasting in practical application. The results show that the structural parameters of the shaped charge have the same influence on the jet head velocity, and there are certain differences in the impact on the jet length. The fitted curve of the support vector machine (SVM) regression model based on the genetic algorithm (GA) is high prediction accurate. By comparing the optimization results with the actual engineering application of the shaped charge structure, the rock breaking effect has been significantly improved, which has important guiding significance for the actual engineering application., Competing Interests: The authors declare no conflict of interest., (© 2022 The Author(s).)

On the western plateau of China, ventilation problems brought on by low atmospheric pressure must be overcome. And CO migration after blasting in high-altitude tunnel by inclined shaft has become a significant scientific issue. In this study, the Computational Fluid Dynamics (CFD) method was used to analyze the flow field characteristics at the junction of the inclined shaft and tunnel. In addition, the effects of different fan opening modes and different initial CO concentration distributions on the ventilation were discussed. The simulation results showed that the main difference in the ventilation wind field was reflected in the position of the vortex region due to the different fan opening modes. Meanwhile, various initial CO concentration distributions showed different migration when there was no air volume difference between the left and right tunnels. Eliminating vortex zones and fully using high velocity airflow could improve relative ventilation efficiency by at least 18%. CO would accumulate in the opposite direction of the tunnel if only one of the fans was turned on. Therefore, a two-stage ventilation scheme was proposed, and the energy consumption was reduced by at least 33%. This research can provide guidance on high-altitude tunnel construction with multiple working faces to improve ventilation efficiency and reduce energy consumption., (© 2022. The Author(s).)

Some rules of the diffractive deep neural network (D 2 NN) are discovered. They reveal that the inner product of any two optical fields in D 2 NN is invariant and the D 2 NN acts as a unitary transformation for optical fields. If the output intensities of the two inputs are separated spatially, the input fields must be orthogonal. These rules imply that the D 2 NN is not only suitable for the classification of general objects but also more suitable for applications aimed at optical orthogonal modes. Our simulation shows the D 2 NN performs well in applications like mode conversion, mode multiplexing/demultiplexing, and optical mode recognition.

We propose a scheme to manipulate the local orbital angular momentum (OAM) of the ultra-broadband (0.1-30 THz) terahertz (THz) waves from the laser-induced short air filament via chirping the few-cycle vortex laser pump. The simulation results show that either the THz vortex pulses with linear azimuth-dependent phases or the THz angular accelerating vortex beams (AAVBs) with nonlinear azimuth-dependent phases can be produced by tuning the chirp parameter of the pump. Thus, the dominant physical mechanism for THz generation can be determined. The THz temporal and transverse spatial distributions can be also controlled by the chirp parameter. Furthermore, their local OAM density distributions present very complex structures because most of the modulated azimuthal intensity and the corresponding local angular helicity distributions are not able to cancel out completely. Via analyzing the simulated THz results at the different pump intensities, we classify the initial pump intensity into three cases. For the low intensity case, the Kerr effect comes into prominence, so the generated THz radiation shall be vortex pulses. While for the high intensity case, the leading plasma effect dominates. In contrast, when the pump intensity is at the medium level, the Kerr nonlinearity and the plasma effect may be comparable and competitive. Basically, THz AAVBs are generated for both high and medium intensity cases. Our study will provide the possibility for studying the optically induced rotation technology more intuitively from the perspective of angular momentum transfer.

The tunneling collapse is the main engineering hazard in the construction of the drilling-and-blasting method. The accurate assessment of the tunneling collapse risk has become a key issue in tunnel construction. As for assessing the tunneling collapse risk and providing basic risk controlling strategies, this research proposes a novel multi-source information fusion approach that combines Bayesian network (BN), cloud model (CM), support vector machine (SVM), Dempster-Shafer (D-S) evidence theory, and Monte Carlo (MC) simulation technique. Those methods (CM, BN, SVM) are used to analyze multi-source information (i.e. statistical data, physical sensors, and expert judgment provided by humans) respectively and construct basic probability assignments (BPAs) of input factors under different risk states. Then, these BPAs will be merged at the decision level to achieve an overall risk evaluation, using an improved D-S evidence theory. The MC technology is proposed to simulate the uncertainty and randomness of data. The novel approach has been successfully applied in the case of the Jinzhupa tunnel of the Pu-Yan Highway (Fujian, China). The results indicate that the developed new multi-source information fusion method is feasible for (a) Fusing multi-source information effectively from different models with a high-risk assessment accuracy of 98.1%; (b) Performing strong robustness to bias, which can achieve acceptable risk assessment accuracy even under a 20% bias; and (c) Exhibiting a more outstanding risk assessment performance (97.9% accuracy) than the single-information model (78.8% accuracy) under a high bias (20%). Since the proposed reliable risk analysis method can efficiently integrate multi-source information with conflicts, uncertainties, and bias, it provides an in-depth analysis of the tunnel collapse and the most critical risk factors, and then appropriate remedial measures can be taken at an early stage., (© 2022. The Author(s).)

The tunnel collapse is one of the most frequent and harmful geological hazards during the construction of highway rock tunnels. As for reducing the occurrence probability of tunnel collapse, a new dynamic risk assessment methodology for the tunnel collapse was established, which combines the Cloud model (CM), the Membership function, and the Bayesian network (BN). During the preparation phase, tunnel collapse risk factors are identified and an index system is constructed. Then, the proposed novel assessment method is used to evaluate the probability of tunnel collapse risk for on-site construction. The probability of tunnel collapse risk in the dynamic process of construction can provide real-time guidance for tunnel construction. Moreover, a typical case study of the Yutangxi tunnel is performed, which belongs to the Pu-Yan Highway Project (Fujian, China). The results show that the dynamic evaluation model is well validated and applied. The risk value of tunnel collapse in a construction cycle is predicted successfully, and on-site construction is guided to reduce the occurrence of tunnel collapse. Besides, it also proves the feasibility of the dynamic evaluation method and its application potential.

Due to the outstanding electronic properties, unique chemical surface termination units and rich elemental compositions, MXenes have become promising candidates for the development of new generation optoelectronic devices. However, there is still a gap between advanced photonics applications and fundamental understanding of ultrafast carrier photo-physics dynamics and a nonlinear optical response in layered MXenes. Here, we present insight into the excited state relaxation processes and nonlinear optical response of few-layer Ti 3 CN and Ti 3 C 2 nanosheets (NSs) via transient absorption spectroscopy and Z-scan measurements. Owing to similar structural compositions, the transient absorption and nonlinear absorption characteristics behave totally opposite. In addition, photo-induced bandgap renormalization and Pauli blocking phenomena exist in Ti 3 C 2 and Ti 3 CN NSs, respectively. The element replacement may be a new strategy for tunable carrier kinetics and nonlinear optical response of MXenes. These research studies may provide insight into ultrafast carrier photo-physics dynamics as well as promote MXene-based advanced photonics and their applications in optoelectronic devices.

A novel single-shot ultrafast all-optical photography with raster principle (OPR) that can capture real-time imaging of ultrafast phenomena is proposed and demonstrated. It consists of a sequentially timed module (STM), spectral-shaping module (SSM), and raster framing camera (RFC). STM and SSM are used for linearly encoding frequency-time mapping and system calibration, respectively. The function of the RFC is sampling the target by microlens arrays and framing on the basis of frequency-time-spatial positions conversion. We demonstrated the recording of transient scenes with the spatial resolution of ∼90lp/mm, the frame number of 12 and the frame rate of 2 trillion frames per second (Tfps) in single-shot. Thanks to its high spatial-temporal resolution, high frame rate (maximum up to 10 Tfps or more) and sufficient frame number, our OPR can observe the dynamic processes with complex spatial structure at the atomic time scale (10 fs∼1ps), which is promising for application in plasma physics, shock waves in laser-induced damage, and dynamics of condensed matter materials.

We present experimentally an obvious enhancement of the terahertz (THz) radiation with two paralleled filaments pumped by two-color laser fields for a full use of a high laser power, compared with single filament. By mapping the 3-dimensional electric trajectories of generated THz fields with a (111) ZnTe crystal, we observe that the total THz polarization from two filaments can be manipulated by varying the time delay between the two orthogonally polarized pumps, which agrees well with the simulations under the photocurrent model. Notably, the power and spectrum of the THz field almost keep unchanged while manipulating the ellipticity of the THz polarization, which is important for a polarization-controllable THz source.

2D PbS nanoplatelets (NPLs) form an emerging class of photoactive materials and have been proposed as robust materials for high-performance optoelectronic devices. However, the main drawback of PbS NPLs is the large lateral size, which inhibits their further investigations and practical applications. In this work, ultra-small 2D PbS NPLs with uniform lateral size (11.2 ± 1.7 nm) and thickness (3.7 ± 0.9 nm, ≈6 layers) have been successfully fabricated by a facile liquid-phase exfoliation approach. Their transient optical response and photo-response behavior are evaluated by femtosecond-resolved transient absorption and photo-electrochemical (PEC) measurements. It is shown that the NPLs-based photodetectors (PDs) exhibit excellent photo-response performance from UV to the visible range, showing extremely high photo-responsivity (27.81 mA W -1 ) and remarkable detectivity (3.96 × 10 10 Jones), which are figures of merit outperforming currently reported PEC-type PDs. The outstanding properties are further analyzed based on the results of first-principle calculations, including electronic band structure and free energies for the oxygen evolution reaction process. This work highlights promising applications of ultra-small 2D PbS NPLs with the potential for breakthrough developments also in other fields of optoelectronic devices., (© 2021 Wiley-VCH GmbH.)

We theoretically and numerically investigate the generation and evolution of different pulsed terahertz (THz) singular beams with an ultrabroad bandwidth (0.1-40 THz) in long gas-plasma filaments induced by a shaped two-color laser field, i.e., a vortex fundamental pulse (ω 0 ) and a Gaussian second harmonic pulse (2ω 0 ). Based on the unidirectional propagation model under group-velocity moving reference frame, the simulating results demonstrate that three different THz singular beams, including the THz necklace beams with a π-stepwise phase profile, the THz angular accelerating vortex beams (AAVBs) with nonlinear phase profile, and the THz vortex beams with linear phase profile, are generated. The THz necklace beams are generated first at millimeter-scale length. Then, with the increase of the filament length, THz AAVBs and THz vortex beams appear in turn almost periodically. Our calculations confirm that all these different THz singular beams result from the coherent superposition of the two collinear THz vortex beams with variable relative amplitudes and conjugated topological charges (TCs), i.e., +2 and -2. These two THz vortex beams could come from the two four-wave mixing (FWM) processes, respectively, i.e., ω 0 +ω 0 -2ω 0 →ω THz and -(ω 0 +ω 0 ) + 2ω 0 →ω THz . The evolution of the different THz singular beams depends on the combined effect of the pump ω 0 -2ω 0 time delay and the separate, periodical, and helical plasma channels. And the TC sign of the generated THz singular beams can be easily controlled by changing the sign of the ω 0 -2ω 0 time delay. We believe that these results will deepen the understanding of the THz singular beam generation mechanism and orbital angular momentum (OAM) conversion in laser induced gas-filamentation.

Ultrafast photonics based on two-dimensional (2D) materials has been used to investigate light-matter interactions and laser generation, as well as light propagation, modulation, and detection. Here, 2D metal-phosphorus trichalcogenides, which are known for applications in catalysis and electrochemical storage, also exhibit advantageous photonic properties as nanoflakes that are only a few layers thick. By using an open-aperture Z-scan system, few-layer NiPS3 nanoflakes exhibited a large modulation depth of 56% and a low saturable intensity of 16 GW cm-2 at 800 nm. When NiPS3 nanoflakes were used as a saturable absorber at 1066 nm, highly stable mode-locked pulses were generated. Thus, these results revealed the nonlinear optical properties of NiPS3 nanoflakes which have potential photonics applications, such as modulators, switches, and thresholding devices.

Atmospheric transmission distortion is one of the main challenges hampering the practical application of a vortex beam (VB) which carries orbital angular momentum (OAM). In this work, we propose and investigate a deep learning based atmospheric turbulence compensation method for correcting the distorted VB and improving the performance of OAM multiplexing communication. A deep convolutional neural network (CNN) model, which can automatically learn the mapping relationship of the intensity distributions of input and the turbulent phase, is well designed. After trained with loads of studying samples, the CNN model possesses a good generalization ability in quickly and accurately predicting equivalent turbulent phase screen, including the untrained turbulent phase screens. The results show that through correction, the mode purity of the distorted VB improves from 39.52% to 98.34% under the turbulence intensity of Cn2 = 1 × 10 -13 . Constructing an OAM multiplexing communication link, the bit-error-rate (BER) of the transmitted signals in each OAM channel is reduced by almost two orders of magnitude under moderate-strong turbulence, and the demodulated constellation diagram also converges well after compensated by the CNN model.

This paper proposes a liquid crystal-based order adjustable q-plate system. The system, which is solid-state and electrically controlled without any mechanical components, consists of several bit cells and one symbol cell. The bit cells can be electrically selected whether to modulate the beam. The magnitude of the order of the q-plate system can be controlled by activating specific bit cells. And the sign of the order can be changed by controlling the voltages in the symbol cell. The whole system can realize the function of the order adjustable q-plate with the order ranging from -2n + 1 to 2n-1 with n bit cells. In our experiment, the system with 4 bits is verified. Based on the q-plate system, the vector beams and optical vortexes with the orders ranging from -15 to 15 can be generated.

Polymer composite films, particularly those based on polymers and layered nanomaterials, are attractive materials for exploiting the properties of multiple materials for applications in electronics and photonics. In this work, a beta-lead oxide quantum dot (β-PbO QD)/polystyrene (PS) composite film is successfully fabricated by a solution blending method. The β-PbO QDs are well-distributed within a β-PbO QD/PS composite film and the composite film is transparent and flexible. Owing to the almost complete insolubility of both β-PbO QDs and PS, the as-fabricated β-PbO QD/PS composite film holds the nonlinear photonic response from 540 nm to 1060 nm under complete water immersion, confirming its excellent stability to high humidity. Additionally, the β-PbO QD/PS composite film exhibits a considerable capacity for optical modulation owing to a strong nonlinear absorption coefficient compared with those of other two-dimensional (2D) materials. On the basis of a home-made β-PbO QD/PS composite film saturable absorber, stable mode-locked pulses at 1060 nm are generated under humid conditions. It is anticipated that the β-PbO QD/PS composite films enable the exploitation of new waterproof, flexible photonic devices based on functional 2D materials and polymers.

Converting a Gaussian mode to a vortex beam is much more inconvenient in the terahertz (THz) region than in the near-infrared (NIR) region due to underdevelopment of THz components and strong THz diffraction. This Letter reports the direct generation of THz vortex pulses by optical difference-frequency between two NIR chirped pulses with different topological charges (TCs). By designing a passive and transmissive device for a collinear NIR pulse pair with conjugated TCs, we have experimentally obtained stable THz vortex pulses with a TC value of 2 or -2. The process needs no THz components and so is flexible to be realized and has promising applications in the THz field.

Vector beams with different polarization topological orders (PTOs) are the eigenmodes of traditional optical fibers and are orthogonal to each other, so the PTO multiplexing channel is a promising candidate for the oncoming generation of optical communication. Here we demonstrate experimentally a PTO sorting system with high separation resolution based on the diffractive splitting (DS) method. Our experiments show that our design with the DS method helps to enhance the separation resolution to 77.5% from 58%, compared to a design without the application of a DS method. Theoretically, to increase the copy number can promote the separation resolution further. This Letter provides a high-resolution way to decode information from PTO division multiplexing.

This publisher's note corrects an error in one of the authors' names and an error in one of the grant numbers in Opt. Lett.42, 4263 (2017).

We propose a common-path spectral interferometer for single-shot terahertz (THz) electro-optics (EO) detection, where a probe pulse pair with orthogonal polarizations and a relative time delay are generated by simply using a birefringent plate. One of them, as the object, transmits through a THz EO crystal with THz phase modulation, while the other goes through the crystal without any phase imposed by target the THz field as the reference. The co-axial propagation of the pulse pair can effectively reduce the noises due to mechanical vibrations, air turbulences, and temperature fluctuations in the traditional non-common-path spectral interferometers. Our experiments show that, for a given target THz pulse field, the measured THz signals in a single-shot mode have a signal-to-noise ratio (SNR) of 41.2 with our THz common-path spectral interferometer, but 7.91 with a THz Mach-Zehnder spectral interferometer; thus, our design improves the SNR of the THz signal by about 5.2 times.

This paper investigates theoretically and numerically on the electro-optical coupling (EOC) for a circular Airy beam (CAB) propagating along the optical axis of a uniaxial crystal after deducing the wave coupling equations of EOC. For a circularly polarized incident CAB, EOC can be used to generate vortex beam by coupling the incident left-handed component into the right-handed vortex component with a vortex topological charge of 2. What's more, EOC plays important role in enhancing or suppressing the abrupt autofocusing, the most important property of CABs, for both left-handed and right-handed components. Near the focal plane, EOC can result in electrically controllable optical "needle" and "cage", which shall be interesting in micromanipulation. In addition, EOC can influence or even forbid the exchange between spin angular momentum (SAM) and orbit angular momentum (OAM). For a linearly polarized incident CAB, its two Cartesian field components of the beam cannot only couple their powers to each other, but also lead to the changes of the intensity pattern and polarization distributions. The polarization state becomes spatially inhomogeneous, and possesses vortex phase with a topological charge of 2 during propagation. EOC presents a new way to control an Airy beam fast and efficiently.

This paper investigates theoretically and numerically the propagation characteristics of a circular Airy beam (CAB) in a uniaxial crystal in detail. The beam loses its boundary cylindrical symmetry during propagation because of the medium anisotropy, although it propagates along the optical axis. This effect of anisotropy on the propagating beam becomes increasingly evident with the increase of the propagation distance. Another main influential factor of the propagation characteristics is the ratio of the extraordinary refractive index to the ordinary refractive index (n e /n o ). The more the value deviates from 1, the worse the symmetry of the beam intensity distribution becomes. The polarization becomes notably complicated, but possesses a vortex state with a topological charge of 2 during propagation. The abruptly autofocusing characteristic, the most important property of CABs, also appears when the crystal length is long enough, which is greatly different from that characteristic in isotropic media. This work is helpful for the design of optical devices based on uniaxial crystals for beams with some special wavefronts.

Comprehensive characterization of ultrafast optical field is critical for ultrashort pulse generation and its application. This paper combines two-step phase-shifting (TSPS) into the spectral phase interferometry for direct electric-field reconstruction (SPIDER) to improve the reconstruction of ultrafast optical-fields. This novel SPIDER can remove experimentally the dc portion occurring in traditional SPIDER method by recording two spectral interferograms with π phase-shifting. As a result, the reconstructed results are much less disturbed by the time delay between the test pulse replicas and the temporal widths of the filter window, thus more reliable. What is more, this SPIDER can work efficiently even the time delay is so small or the measured bandwidth is so narrow that strong overlap happens between the dc and ac portions, which allows it to be able to characterize the test pulses with complicated temporal/spectral structures or narrow bandwidths.

Background: Rhamnolipids were reported to have evident antifungal activity. The efficacy of rhamnolipids against Alternaria alternata and their possible mechanisms involved were investigated., Result: The decay incidences of A. alternata of cherry tomatoes (Lycopersicon esculentum) treated by rhamnolipids were significantly reduced. The in vitro assays showed that rhamnolipids inhibited fungal growth on solid medium and prevented spore germination and mycelium growth in liquid medium. In addition, the combination of rhamnolipids and essential oil had a synergistic effect leading to the decrease of fungicidal concentrations of laurel oil. Scanning electron microscopy and transmission electron microscopy observations of the pathogen revealed significant morphological and cell structural alterations in the hyphae. Compared to the control, the content of nucleic acid in supernatant of the suspension of A. alternata increased, while the content of DNA and protein of mycelium decreased, which was in agreement with electrolyte leakage experiments., Conclusion: Rhamnolipids could be an alternative to chemicals for controlling post-harvest phytopathogenic fungi on fruits and vegetables., (© 2014 Society of Chemical Industry.)

Background: Essential oils such as citronella oil exhibit antifungal activity and are potential alternative inhibitors to chemical synthetic fungicides for controlling postharvest diseases. In this study the antifungal activity of citronella oil against Alternaria alternata was investigated., Results: In vitro, citronella oil showed strong inhibition activity against A. alternata. The minimum inhibitory concentration in potato dextrose agar and potato dextrose broth medium was determined as 1 and 0.8 µL mL(-1) respectively. In vivo the disease incidence of Lycopersicon esculentum (cherry tomato) treated with citronella oil was significantly (P < 0.05) reduced compared with the control after 5 days of storage at 25 °C and 95% relative humidity. The disease incidence at oil concentrations of 0.2-1.5 µL mL(-1) was 88-48%. The most effective dosage of the oil was 1.5 µL mL(-1), with 52% reduction, and the oil had no negative effect on fruit quality. Scanning electron microscopy observation revealed considerably abnormal mycelial morphology., Conclusion: Citronella oil can significantly inhibit A. alternata in vitro and in vivo and has potential as a promising natural product for controlling black rot in cherry tomato., (© 2014 Society of Chemical Industry.)

We present a modified THz electro-optic sampling method to combine the advantages of its two traditional counterparts at near 0° and 45° optical biases: excellent ability to cancel the background noises, high optical modulation, and large dynamical range. The first advantage results from the method's symmetrical layout to get dynamical noise cancellation. By setting the static birefringent phases of the two balanced beams with a pair of opposite numbers, our setup can record THz waveforms without distortion with its maximal modulation depth, thus optimal signal-to-noise ratio (SNR). The setting also releases the linearity of the measured signal from the static birefringence, thus enlarging greatly the linear dynamical range. For a given THz field, the recorded SNR with our setup, without a lock-in, is more than 10 times higher than that with the "crossed and balanced" design [IEEE Trans. Microwave Theory Tech. 47, 2644 (1999)].

Background: Many essential oils were reported to be used as natural, environmental friendly antimicrobial agents. The antifungal activity in vitro and in vivo of an essential oil extracted from Chinese local Laurus nobilis leaves against Alternaria alternata has been studied., Result: The main components of the essential oil were investigated by means of gas chromatography–mass spectrometry and 14 components were identified. The main ones were eugenol, caryophyllene and cinnamaldehyde. The antifungal test showed that at 800 μg mL−1 of L. nobilis oil completely inhibited the growth of A. alternata. In addition, the conidial germination of the pathogen was significantly inhibited at 200 μgmL−1, and the weight of mycelia efficiently decreased at 500 μgmL−1. The in vivo assay indicated that 500 μg mL−1 L. nobilis oil was effective in protecting cherry tomatoes (Lycopersicon esculentum)from infection of A. alternata, with an inhibition ratio of 33.9%. Scanning electron microscopy observations of the pathogen revealed significant morphological alterations in the hyphae., Conclusion: This work suggested that L. nobilis oil could be used as a potential fungicide to control the post-harvest disease caused by A. alternata.

This paper presents a novel design for broadband zero-order half-wave plates to eliminate the first-order or up to second-order wavelength-dependent birefringent phase retardation (BPR) with 2 or 3 different birefringent materials. The residual BPRs of the plates increase monotonously with the wavelength deviation from a selected wavelength, so the plates are applicable to the broadband light pulses which gather most of the light energy around their central wavelengths. The model chooses the materials by the birefringent dispersion coefficient and evaluates the performances of the plates by the weighted average of the absolute value of residual BPR in order to emphasize the contributions of the incident spectral components whose possess higher energies.

This paper presents a novel design for getting high signal-noise ratio broadband terahertz signal through intracavity optical rectification together with terahertz EO sampling. A nonlinear crystal as terahertz emitter is positioned inside a femtosecond laser oscillator under Brewster angle pumping configuration in order to scale up the pumping pulse power but to keep high pulse repetition rate. Our experiments show that the compact and cost-effective design improves the signal-noise ratio by about 29 times compared with the counterpart based on extracavity nonlinear optical rectification. This work opens a new way to improve the signal-noise ratio of the free-space terahertz time-domain spectroscopy through nonlinear optical rectification pumped by a femtosecond laser oscillator.

Reflection of waves at planar interfaces associated with a uniaxial medium is theoretically analyzed by examining the boundary condition and the dispersion relation. Simple global expressions of incident and reflected angles of both wave vectors and ray vectors are derived. The relations between them are obtained. It is also shown that negative reflection can be realized in all uniaxial media under certain conditions. Our results offer considerable potential device applications of uniaxial media.

This paper presents our detailedly theoretical analyses on omnidirectional constant transmission and negative Brewster angle at planar interfaces associated with a uniaxial medium. The amplitude reflection and transmission coefficients at planar interfaces associated with uniaxial media are derived by examining the boundary condition and the dispersion relation. It is found that under certain conditions, the coefficients are constants independent of the incident angle. Another interesting phenomenon is that an interface between isotropic and uniaxial media can exhibit negative refraction under Brewster condition. Our results offer considerable potential device applications of uniaxial media.

This paper presents the first experimental observation of interband photo- refractive (PR) effects in beta-BBO crystal due to multiphoton excitation with intense ultrashort pulses. In order to fully characterize the PR effects, a sensitive intracavity scheme is developed to magnify the dynamics of nonlinear lenses induced by the PR effects. The reproducible PR phenomena depend strongly on the power, wavelength, and spatial intensity profile of the intense laser pulses and the electro-optic coefficient of the optical materials. Its response time is from tens of seconds to several minutes. The results may be very helpful for us to find a solution to overcome the deleterious influence of multiphoton induced photo-charges on nonlinear optical frequency conversions, e.g. optical parametric chirped pulse amplification.

A straightforward all-optical way is demonstrated to synchronize broadband pulses of Ti:sapphire lasers with pulses at 1064 nm, wherein background-free pulses around 1064 nm are generated by non-collinear optical parametric amplification seeded with an intracavity continuous-wave He-Ne laser. The intracavity He-Ne laser provides sufficient seed power to dominate over parametric fluorescence. With an intracavity power of 200 mW, the idler pulse at 1064 nm has the pulse-energy about 6 nJ.

We demonstrated efficient laser action of a new ytterbium-doped oxyorthosilicate crystal Yb:LuYSiO(5) (Yb:LYSO) under high-power diode-pumping. The spectroscopic features and laser performance of the alloyed oxyorthosilicate crystal are compared with those of ytterbium-doped lutetium and yttrium oxyorthosilicates. In the continuous-wave laser operation of Yb:LYSO, a maximal slope efficiency of 96% and output power of 7.8 W were respectively achieved with different pump sources. The Yb:LYSO laser exhibits not only little sensitivity to the pump wavelength drift but also a broad tunability. By using a dispersive prism as the intracavity tuning element, we demonstrated that the continuous-wave Yb:LYSO laser exhibit a continuous tunability in the spectral range of 1014-1091 nm.

All-optical synchronization of 1064 nm pulses with femtosecond laser pulses at 794 nm is realized on the basis of continuous-wave laser seeded non-collinear optical parametric amplification, by using a CW laser at 632.8 nm as the seeded signal and intense frequency-doubled Ti:sapphire femtosecond laser at 396 nm as the pumping source. The generated background-free idler pulses at 1064 nm can be used as an accurately synchronized pump seed for the optical parametric amplification of ultra-broadband chirped Ti:sapphire laser pulses.

Single-longitudinal-mode operation is achieved in a twisted-mode-cavity c-cut Nd:GdVO4 laser. With a semiconductor saturable absorption mirror as an intracavity saturable absorber to launch passive Q-switching, no mode-locked spikes are observed on the temporal envelopes of the Q-switched output pulses due to the complete elimination of spatial hole burning in the gain medium to suppress longitudinal multi-modes. The maximal average output power is 1.24 W with the repetition rate of 76.3 kHz, and the single pulse energy is 16.0 microJ. The pulse width and polarization ratio of the output laser beam are measured about 150 ns and 53:1, respectively.