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In recent years, high-power, tunable terahertz (THZ) radiation sources have become the key areas of research in the world. The method of THZ waves by nonlinear optical difference frequency generation (DFG) has the advantages of wide tuning, high power, room temperature operation, and compact structure. However, the conversion efficiency of the current difference frequency method is low, which needs a trade-off between conversion efficiency and tuning range. We apply the nonlinear optical cascade difference frequency conversion theory based on stimulated Raman adiabatic passage (STIRAP) and propose a theoretical scheme to generate THZ waves. Numerical simulation investigates the cascaded difference frequency process of generating THZ waves with the help of the nonlinear medium lithium niobate (LN) crystal. The theoretical analysis shows that the maximum quantum conversion efficiency from signal laser to THZ waves is 43.2 % when the wavelength of the tuned signal laser varies between 1.044 − 1.065 µm with the fixed two pump laser wavelengths constant. The tunable THZ waves of 0.48 − 5.0 THz can be obtained and the maximum output intensity of THZ waves is 2.17 MW/cm2, and the method is robust to temperature variations. It also provides a novel idea for the cascaded difference frequency generation of THZ waves.

Zinc citrate (ZC) has been widely used in food as an important nutritional supplement. Accurate detection of ZC in food is important for health and safety. In this study, THz time-domain spectroscopy (THz-TDS) is used to quantitatively detect ZC in flour and milk powder mixtures. In our research, 15 different contents of ZC in flour and milk powder mixtures were prepared and measured by THz-TDS. A partial least squares (PLS) model was established based on the quantitative analysis of the absorption coefficient data of these two mixtures at 0.5–3.0 THz. The R 2 and rms error (RMSE) given by the PLS model prediction were, respectively, 0.999 and 0.14% ZC in flour and 0.999 and 0.20% ZC in milk mixtures, indicating the predictions of the PLS model are in excellent agreement with the experimental measurements. The results show that combining THz-TDS with the PLS model can be used for accurate, quantitative analyses of ZC in food mixtures.

We investigate the propagation dynamics of the Pearcey-Gaussian (PG) pulses in the presence of time-dependent potentials in a linear medium both theoretically and numerically. We demonstrate that the combination of the linear potential and the initial chirp of PG pulses can flexibly control the propagation trajectory and inherent focusing properties of the PG pulses. When the parabolic potential is taken into account, the chirped PG pulses are periodically focused and reversed. By adjusting the parabolic potential and the pulse chirp, the characteristics of the focal points, such as position, intensity, and spacing between focal points, can be manipulated effectively. The interaction of two temporally separated PG pulses still shows a periodic evolution with controllable focusing characteristics. These results can broaden the application range of PG pulses and provide some inspiration for the control of PG pulses under nonlinear conditions.

We propose a nonvolatile, reconfigurable, and narrowband mid-infrared bandpass filter based on surface lattice resonance in phase-change material Ge2Sb2Te5. The proposed filter is composed of a two-dimensional gold nanorod array embedded in a thick Ge2Sb2Te5 film. Results show that when Ge2Sb2Te5 transits from the amorphous state to the crystalline state, the narrowband reflection spectrum of the proposed filter is tuned from 3.197 &mu, m to 4.795 &mu, m, covering the majority of the mid-infrared regime, the peak reflectance decreases from 72.6% to 25.8%, and the corresponding quality factor decreases from 19.6 to 10.3. We show that the spectral tuning range can be adjusted by varying the incidence angle or the lattice period. By properly designing the gold nanorod sizes, we also show that the quality factor can be greatly increased to 70 at the cost of relatively smaller peak reflection efficiencies, and that the peak reflection efficiency can be further increased to 80% at the cost of relatively smaller quality factors. We expect that this work will advance the engineering of Ge2Sb2Te5-based nonvalatile tunable surface lattice resonances and will promote their applications especially in reconfigurable narrowband filters.

This paper proposes a theoretical scheme to synthesize white laser source based on the cascaded sum frequency generation (CSFG) model with stimulated Raman adiabatic passage (STIRAP). In the CSFG model, the signal laser, intermediate laser and output laser correspond to red, green and blue (RGB) lasers respectively. The results show that in general the red laser is completely converted to the blue laser, and there is no apparent intermediate green laser. Moreover, under the counterintuitive order, the pump parameters have a wider adjustment range of system conversion efficiency than the coupling delay parameters. We synthesize the white laser source through the following steps. First, we change the pump intensity to roughly adjust the conversion efficiency of the system, and then vary the coupling delay parameters to fine-tune RGB lasers output power ratio. Compared with the scheme based on frequency conversion with Stark-chirped rapid adiabatic passage to synthesize white laser source, the RGB lasers output of the new scheme can achieve better stability. The results of the investigation can provide a theoretical foundation for the research of novel optical devices.

Functional near-infrared spectroscopy (fNIRS) was used to investigate the stability of resting state functional connectivity (RSFC) in the prefrontal cortex. In a longitudinal study for investigating the stability of RSFC with time, we recruited 6 healthy adult subjects to undergo a 10-min resting state fNIRS scan once per day for 7 consecutive days. In a cross-sectional study, 62 healthy subjects underwent a single 10-min RSFC measurement. Three regions-of-interest (ROIs) were studied, the superior frontal gyrus (SFG), the middle frontal gyrus (MFG), and the inferior frontal gyrus (IFG). Homologous RSFC between the left and right hemisphere was computed for each ROI. The longitudinal RSFC study showed no significant variation with time in each ROI, implying that a one-time scan was sufficient for evaluating RSFC for an individual. The cross-sectional study showed significant difference in RSFC between SFG and MFG/IFG. Based on these observations, a lower bound of RSFC with an 85% confidence level for healthy adults was given for each gender: in IFG, 0.6894 (male) and 0.5392 (female), in MFG, 0.6487 (male) and 0.5713 (female), and in SFG: 0.8042(male) and 0.7436(female). To test ability of the lower bound to differentiate between healthy adults and adults with neurological disorders (showing weaker RSFC), 15 patients with affective disorders or sleep disorder were recruited for the resting state scan. The results showed that IFG was the most predictive ROI. This study may help to establish a quantitative range of RSFC for healthy adults and serve as a reference for screening patients with neurological disorders.

We report on the measurements of the effective line intensities of the ν1 fundamental band of trans-nitrous acid (trans-HONO) in the infrared near 3600 cm−1 (2.78 µm). A home-made widely tunable laser spectrometer based on difference-frequency generation (DFG) was used for this study. The strengths of 28 well-resolved absorption lines of the ν1 band were determined by scaling their absorption intensities to the well referenced absorption line intensity of the ν3 band of trans-HONO around 1250 cm−1 recorded simultaneously with the help of a DFB quantum cascade laser (QCL) spectrometer. The maximum measurement uncertainty of 12% in the line intensities is mainly determined by the uncertainty announced in the referenced line intensities, while the measurement precision in frequency positions of the absorption lines is better than 6×10−4 cm−1. The cross-measurement carried out in the present work allows one to perform intensity calibration using well referenced line parameters.

We have theoretically studied the generation rate of longitudinal optical (LO) phonons in mid-infrared quantum cascade laser so as to learn the effect of phonons on electron transmission characteristics. The LO phonon performance was analyzed by combining the Monte-Carlo simulation with kinetic equations. We have obtained the LO phonon number under different applied field to show that the generating rate and the saturating number of optical phonon increases with applied field. At last we propose the pulsed pumping to point out the importance of LO phonon decaying into two acoustic phonons in electron transmission.

Here we report a tunable polarization-independent broadband absorber in the terahertz regime. The proposed structure consists of periodic all-dielectric array on a gold substrate, sandwiched by a monolayer graphene and an epsilon-near-zero layer. Simulation results show that the absorption that is independent from the incident polarization remains above 90% over a broadband spectral range from 1.6 THz to 4.1 THz, corresponding to a bandwidth of 2.5 THz and a relative bandwidth of 87.7%. By varying the graphenes Fermi energy from 0.2 eV to 0.5 eV, the absorption bandwidth can be turned from 1.5 THz to 2.5 THz. We expect this polarization- independent absorber with dynamically tunable bandwidth can be used a filters in applications such as terahertz detectors.

We report the design an ultra-broadband highly reflective subwavelength grating that covers almost the entire visible region. Results show that high reflectivity above 90% covering 450–700 nm can be achieved, corresponding to Δλ/λ=43%. We also provide intuitive physical insights into the broadband high reflection performance of reflector. We expect that this ultra-thin, ultra-broadband and highly reflective all-dielectric reflector can find applications in hyperspectral imaging based on tunable etalon filters.

We propose a novel configuration for nonvolatile and reconfigurable tuning of surface lattice resonances (SLRs) based on thin films of phase-change material Ge2Sb2Te5 (GST). The configuration is composed of gold nanorod array embedded in a thin GST film. Results show that, an extremely wide SLR wavelength tuning range reaching 1600 nm, large tuning figure of merit of 21, and high SLR quality factors of 47 and 17 can be achieved in the mid-infrared regime when GST transits from the amorphous state into the crystalline state. The effects of the GST layer thicknesses on the SLR tuning performance are discussed, and the performances of several modified configurations are compared. We expect this work will advance the engineering of SLR tuning based on phase-change materials and promote its applications especially in nanolasing and narrowband filtering.

In this paper, an efficient cascaded sum frequency generation (SFG) model based on Stark-chirped rapid adiabatic passage is established, in which the laser of signal, intermediate, and output corresponds to three primary, and an approach of white laser source synthesis is proposed. The research results show that the energy of the red laser can be almost converted into blue laser, while the green laser intensity is extremely low in the cascade SFG process. The farther away from the optimal coupling delay parameters, the smaller the corresponding conversion efficiency is. Meanwhile, the pump intensity has a larger control range for conversion efficiency. On the basis of these findings, a white laser source with a color temperature of 6500 K can be synthesized. We first roughly adjust the pump intensity to reduce the conversion efficiency so that the red, green and blue lasers coexist at the output. Then, we fine-tune the coupling delay parameters so that the output power ratio meets 0.61:0.28:0.11. These research results can provide a theoretical basis for achieving efficient frequency conversion and the development of new optical devices.

We investigate the influence of nonlinear crystal’s coupling modulation on wavelength conversion based on Stark-chirped rapid adiabatic passage. The result shows that the distribution of the efficient conversion is zonal with the change of coupling delay parameter. In addition, the efficient wavelength conversion can be performed in counterintuitive and intuitive order, which can reduce the restriction on the condition of conversion process compared to the stimulated Raman adiabatic passage. When the width parameter d 1 2 is fixed, the larger the width parameter d 2 2 is, the higher the maximum conversion efficiency is and the larger the bandwidth for efficient wavelength conversion is. These findings provide a theoretical basis for the efficient acquisition of laser sources from the visible to the mid-infrared and to the ultraviolet.

We report the design of broadband highly reflective subwavelength high-index-contrast gratings (HCGs) for both TE and TM polarizations in the visible regime. Results show that high reflectivity above 99% covering 544–726 nm or 510–666 nm can be achieved, corresponding to a fractional bandwidth of Δλ/λ0 = 28.7% or 26.5% for the TM or TE polarization, respectively. We reveal that these broad high-reflectivity bands originate from a blend of multiple leaky modes, similar to the counterparts operating in the near-infrared regime. By investigating the effects of the grating height, period, and width, we find that the broadband high reflectivity requires careful optimization. We expect that this work will advance the engineering of broadband HCG reflectors and promote their applications in the visible regime.

In an attempt to find potential pesticides derived from natural products, a novel series of essential oils-oriented chiral esters have been designed and synthesized based on the scaffold of natural pyrethrin. The newly synthesized compounds were screened for their potential insecticidal activity against Plutella xylostella , and the preliminary results revealed that about half of the target compounds' activities have been significantly improved comparing with the essential oil molecules, and some compounds exhibited better insecticidal activity in contrast to the commercialized specie of d - trans -Phenothrin at the concentration of 3.7 mg/L.

Bacterial leaf blight, caused by Xanthomonas oryzae pv. oryzae , is one of the most destructive diseases of rice worldwide. N -acetylglucosamine-1-phosphate uridyltransferase (GlmU) was an attractive target for the development of antimicrobial agents. To develop novel, more potent and even more selective inhibitors of the uridyltransferase activity of Xanthomonas oryzae pv. oryzae GlmU (Xo-GlmU), three types of novel target compounds were optimized and synthesized based on the Xo-GlmU structure in this study. The biological testing results showed that all of the target compounds displayed the higher inhibition than the lead compound with the IC 50 values in the 10.82–23.31 µM range, and the inhibition rates were increased by 30%–67%. The binding mode and the possible inhibitory mechanism of the target compounds in the active site were also analyzed by the molecular docking based on the uridyltransferase active site of Xo-GlmU.

Most material properties can be traced to electronic structures. Black silicon produced from SF6 or sulfur powder via irradiation with femtosecond laser pulses displays decreased infrared absorption after annealing, with almost no corresponding change in visible light absorption. The high-intensity laser pulses destroy the original crystal structure, and the doping element changes the material performance. In this work, the structural and electronic properties of several sulfur-doped silicon systems are investigated using first principle calculations. Depending on the sulfur concentration (level of doping) and the behavior of the sulfur atoms in the silicon lattice, different states or an absence of states are exhibited, compared with the undoped system. Moreover, the visible-infrared light absorption intensities are structure specific. The results of our theoretical calculations show that the conversion efficiency of sulfur-doped silicon solar cells depends on the sulfur concentrations. Additionally, two types of defect configurations exhibit light absorption characteristics that differ from the other configurations. These two structures produce a rapid increase in the theoretical photoelectric conversion efficiency in the range of the specific chemical potential studied. By controlling the positions of the atomic sulfur and the sulfur concentration in the preparation process, an efficient photovoltaic (PV) material may be obtainable.

Three series of novel peptidomimetics bearing the tryptamine moiety were designed, synthesized, and evaluated for their inhibition activities against cell proliferation. According to the preliminary studies on cytotoxic activities, some of the newly prepared compounds (Ia–k, IIa–d, IIIa–g) displayed significant inhibition activities against human hepatoma cancer (HepG2 and Huh-7), and human melanoma (A875) cell lines compared with the control 5-fluorouracil. Especially, compounds Ih and Ij exhibited obvious inhibition activities (Ih IC50 = 4.88 ± 0.78 μg mL−1; Ij IC50 = 6.60 ± 1.20 μg mL−1) against 5-fluorouracil-resistant human hepatocellular carcinoma (BEL-7402/5-FU) cell lines.

To evaluate the possibility of sensitive detection of Cry1Ab protein in vivo and in vitro, polyamidoamine (PAMAM) dendrimers functionalized CdTeSe QDs were prepared by using solvent evaporation method and Cry1Ab was bound on the surface of NIR QDs through hydrogen bond. Transmission electron microscope (TEM) was used to examine the structure and properties of PAMAM-functionalized CdTeSe quantum dots. Fluorescence microscopy was used to detect the fluorescence of the nanoparticles. The results showed that PAMAM-functionalized CdTeSe QDs can detect Cry1Ab protein both in vitro and in vivo with sensitivity. In vitro, the enhanced fluorescence (FL) intensity as a function of concentration matched Langmuir binding isotherm equation very well in the range of 0–200 ng/mL of Cry1Ab proteins. The detection limit of this method was found to be 3 ng/mL. In vivo, the water-soluble NIR-QD nanoparticles were found in the midgut of pest by fluorescence microscopy, indicating that these bioprobes are useful for real-time detection of Cry1Ab. The prepared PAMAM functionalized QDs could serve as excellent NIR optical imaging probes to detect the transgenic ingredients in genetically modified (GM) research.

Acetohydroxyacid synthase (AHAS, EC: 2.2.1.6) is a target for the development of novel herbicides. Two series of N-nitrophenyl derivatives, type-A and type-B, were designed and synthesized based on the active site of the AHAS structure. All the structures of newly prepared compounds were thorough characterized by IR, and 1H NMR spectrums. The IC50 values of all synthesized target compounds against AHAS enzyme and EC50 values for herbicidal activity against Brassica campestris L., Amaranthus mangostanus L. and Sorghum sudanense were determined. The bioactive assay results showed that the type-B compounds exhibited highly improved inhibitory activity against the AHAS enzyme and the tested plants comparing to type-A compounds. The IC50 values of most type-B compounds against the AHAS enzyme were between 25–177 μM. The EC50 values of several type-B compounds against Sorghum sudanense reached 5.0 mg/L. The differences in the biological activity between type-A and type-B compounds were attributed to two structural features - the orthogonal bend at the N-nitro amides group and the common plane structure of another phenyl with chain bridge. With the structure of the target compounds and the IC50 values for AHAS enzyme, a statistically significant CoMFA model with high predict abilities (q2 = 0.606, r2 = 0.982, N = 4, SEE = 0.058, F = 280.255) was obtained, and its reliability was verified. The model will provide a theoretical basis for the further structural optimization.

To explore the characteristics of light propagation along the Pericardium Meridian and its surrounding areas at human wrist by using optical experiment and Monte Carlo method.An experiment was carried out to obtain the distribution of diffuse light on Pericardium Meridian line and its surrounding areas at the wrist, and then a simplified model based on the anatomical structure was proposed to simulate the light transportation within the same area by using Monte Carlo method.The experimental results showed strong accordance with the Monte Carlo simulation that the light propagation along the Pericardium Meridian had an advantage over its surrounding areas at the wrist.The advantage of light transport along Pericardium Merdian line was related to components and structure of tissue, also the anatomical structure of the area that the Pericardium Meridian line runs.

In the field of nonlinear frequency conversion, the cascaded frequency conversion scheme is an effective means to obtain new wavelengths. In this paper, we demonstrate efficient frequency conversion through three cascaded three-wave mixing processes based on Stark-chirped rapid adiabatic passage, which are different from previous cascaded wavelength conversion processes based on stimulated Raman adiabatic passage. Further, by analyzing the relevant parameters in the three-process cascaded frequency conversion models we have established, we find that the new scheme increases the conversion range and has lower restrictions on the conversion conditions while maintaining extremely low intermediate frequency intensity. These advantages allow our work to be applied to the acquisition of a mid-infrared or visible laser.

In this paper, a two-phonon-resonance terahertz quantum cascade laser (THz QCL) based on GaN/AlGaN material system is proposed. GaN/AlGaN material system is first studied in two-phonon-resonance active region structure by using rate equations. The active region adds an energy state above the upper laser state. The energy state difference between additional state and the upper laser state is equal to the longitudinal optical phonon energy which has a large magnitude (~90 meV). The simulation results show that the proposed THz QCL can get better optical properties compared with the traditional three-level active region building in the same material system and has the superiority in improving electronic utilization. The results also show that two-phonon-resonance THz QCL based on GaN/AlGaN material system can gain the peak output power of 8 mW at the temperature of 230 K.

In the present study, a simple and inexpensive method for the simultaneous determination of 22 pesticides in aquatic vegetables by HPLC spectrum analyses with diode array detector (HPLC–DAD) is established. The proposed method is also applied for the analyses of pesticides residues in water chestnut, lotus root, and wild rice shoots, and the results indicate that this method could meet the requirements for simultaneous determination of the pesticides. The calibration showed good linearity for all the tested pesticides with correlation coefficients of 0.9936–0.9994. Recoveries for the studied 22 pesticides at their three spiked concentration levels in water chestnut ranged from 73.5 to 108.3 %, with relative standard deviations of 1.7–12.5 %. Limits of quantitation for the analytes were estimated to range between 0.01 and 10.00 mg kg−1.

A series of novel N -nitroacetamides derived from 2,4-dichlorophenoxyacetic acid (2,4-D, a important plant growth regulator) have been conveniently obtained via multi-step reactions including oxidation, bromination, nitration, chlorination, and acylation reactions. All the structures of newly prepared compounds were thoroughly characterized by satisfied IR, 1 H NMR, and 13 C NMR spectrums. The herbicidal activity and plant growth regulating activities of target compounds were also assessed. The preliminary bioassay results showed that these novel N -nitroacetamide derivatives exhibited good herbicidal activity against both dicotyledonous and monocotyledonous weeds. Meanwhile, some of the target compounds displayed high plant growth regulating activity against Rice at the dosage of 0.1 mg/L. The further in vitro inhibition activity against acetohydroxyacid synthase (AHAS) enzyme and molecular docking indicated that AHAS might be the primary target site for these newly synthesized compounds.

Four aroylhydrazine-amides receptors AR1-4 with a hydrazine spacer have been designed, synthesised and characterised as novel colorimetric chemosensors by typical spectroscopic techniques. The receptors AR1–3 exhibited certainly selectivity and sensitivity towards F− and AcO− , forming 1:1 stoichiometry complex by hydrogen-bond interaction. Furthermore, AR4 has especially shown obvious colour change in the presence of these two important biologically anions.

An efficient wavelength conversion scheme based on amplitude modulation is proposed, and it demonstrated by mathematical formulate in an MgO-doped LiNbO 3 quasi-phase-matched waveguide. This method is based on the adiabatic physical process of two-state systems. By nonlinear modulate the overlap of waveguide modes to achieve the purposes of phase-matching and modulate the coupling coefficient. Under the adiabatic constraints condition, we simulate numerically difference frequency generation process. The results shown that this scheme can lead to almost complete transfer of energy from near-IR (~1064 nm) to mid-IR (~3.53 µm) in a stable manner. Furthermore, we also present two analytically exactly soluble models, in which the coupling coefficient is a linear function of propagation distance and the phase mismatch is a constant.

3-5 μm mid-infrared wave band is in the atmosphere window, it has lots of promising applications on the spectroscopy, remote sensing, medical treatment, environmental protection and military affairs. So, it has been a hot topic around the world to research the lasers at this wave band. In recent years, adiabatic passage technology has been applied in frequency conversion area, which borrowed from atomic physics. In this paper we will introduce efficient nonlinear optics frequency conversion by suing this technology.

A series of novel peptidomimetics bearing dehydroepiandrosterone moiety were designed, synthesized, and evaluated for their inhibition activities against cell proliferation. According to the preliminary studies on inhibitory activities, some of the newly prepared compounds indicated significantly inhibition activities against human hepatoma cancer (HepG2), human lung cancer (A549), human melanoma (A875) cell lines compared with the control 5-fluorouracil. Especially, compounds Ii (IC50 Ik (IC50 Ik induced apoptosis in HepG2 cells were analyzed by flow cytometry, and the apoptotic effects of compound Ik were further evaluated using Annexin V-FITC/propidium iodide dual staining assay, which revealed these highly potential compounds induced cell death in HepG2 cells at least partly by apoptosis.

The weeds are a primary reason causing the yield decreasing of agriculture. Acetohydroxyacid synthase (AHAS, EC: 2.2.1.6) is the key target enzyme of many kinds of herbicides, such as sulfonylureas and imidazolinones, the requirements toward the novel herbicide is urgent owing to the gradually emerging resistance with the long-term application. N -nitrourea compounds are a novel urea compounds owning various effects, such as growth regulation, weeding, bacteriostasis. In this study, α-[ N -nitro- N -(2,4,6-triCl) phenyl] leucine ethyl ester urea (compound 3g), a novel N -nitrourea compound, was discovered as a potential lead compound for the AHAS target. Based on the molecular docking analysis compound 3g optimization work was performed, and then a new structure backbone of N -nitrourea compound was designed for further research.