Spectral Overlapping Research Articles

Hybrid photonic-plasmonic photoelectrode for enhanced photoelectrochemical current generation

Photoelectrochemical (PEC) reactions realized through the nonradiative decay of plasmonic process in metallic nanostructure earned tremendous potential to harvest solar irradiance. In conventional metal-semiconductor photoelectrodes, the electric field confinement using optical resonating modes is crucial to instigate plasmonic charge for enhanced photocurrent generation. However, the effect of such resonant states in a semiconductor-free plasmonic photoelectrode is limitedly explored. In this essence, we have experimentally realized a Schottky junction-free plasmonic-photonic hybrid photoelectrode consisting of one-dimensional porous grating of gold nanoparticles (GNPs) on top of a ITO waveguide. This designed photoelectrode exhibits PEC photocurrent generation solely from plasmonic hole transfer to the molecules/ions at the metal-adsorbed water interface. Spectral overlapping of plasmonic activities with photonic modes and porosity-induced large metal-electrolyte interface surface area further enhance the charge generation and transfer. In the results, the GNPs photoelectrode recorded 3.4 and 12.6-fold increases in the incident photon to electron conversion efficiency (IPCE) in contrast to conventional gold bar grating photonic crystal and random GNPs photoelectrodes, respectively. Further, modal coupling of resonant states witnesses a substantial rise in the photocurrent generation than the uncoupled resonant states. The present report delivers a facile strategy for tailoring the plasmonic photocurrent generation in futuristic solar energy harvesting applications.

A deep learning method to separate fluorophores based on their fluorescence lifetime.

Fluorescence lifetime in biological samples is a useful feature to demultiplex the fluorescence signal of spectrally overlapping fluorophores. A problem that frequently occurs when multiple fluorophores are in use is the possible spectral overlap. Therefore, selected fluorophores should be chosen to avoid this issue, consequently constraining the number and the type of fluorophores that can be used at the same time on one sample. Moreover the ability to discriminate fluorophores from temporal information does not come from their own emission spectra, but from the (fluorescent-life) time information. A well-established method for the analysis of lifetime images is the phasor approach. The phasor approach works in the frequency domain and requires no a priori information on the lifetime of fluorophores in the sample. However, the phasor method is based on the linear separation of components and does not exploit the whole information contained in the lifetime data. In this work, we propose a method to separate the contribute from two spectrally overlapping fluorophores based on fluorescence lifetime. We trained a neural network with synthetic and real images of cells stained with two spectrally overlapped fluorochromes. Future development will aim to extend our approach to our fluorescence lifetime image scanning microscopy platform, to extend the method for more than two spectrally overlapping species and to find new features in order to depend less on the training set.

Mass Spectrometric Multiplex Detection of MicroRNA and Protein Biomarkers for Liver Cancer.

The occurrence of cancers is often accompanied by the abnormal expression of several sorts of biomarkers (e.g., nucleic acids and proteins). The multiplex assessment of them would substantially aid in the early detection and precise diagnosis, which is often hampered by their different detection schemes, different reaction matrix and reagents, and spectral overlapping. Herein, we propose a simple and sensitive mass spectrometric method for the multiplex detection of nucleic acid and protein, in which liver cancer-related biomarkers miRNA 223 and alpha-fetoprotein (AFP) were selected as model analytes. The self-amplification effect of metal atom-based nanoparticle probes can provide high sensitivity in complex serum samples without any additional amplification procedure. The detection limits for the simultaneous detection of miRNA 223 and AFP were 103 (2.1 pM) and 219 amol (0.15 ng/mL), respectively, with high specificity and selectivity. The proposed method is potentially useful for the rapid screening of cancers.

Digital Domain Power Division Multiplexing Optical OFDM for Free Space Optical Communication (FSOC) Using 10-GHz Bandwidth Optical Components

We put forward and provide the first illustration of a high capacity and high spectral efficient free space optical communication (FSOC) system using digital domain power division multiplexing orthogonal-frequency-division-multiplexed (DDPD-O-OFDM) signal utilizing 10-GHz class optical components. In the proof-of-concept demonstration, a data rate of 2 × 30.8 Gbit/s can be achieved for each polarization multiplexed wavelength channel, fulfilling the pre-forward-error-correction bit-error-ratio (pre-FEC BER = 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> ). By employing the DDPD-O-OFDM here, the FSOC per channel capacity can be enhanced not only allowing the spectral overlapping of different orthogonal subcarriers, as in the case of OFDM; but also allowing channel multiplexing in the power domain to increase the spectral efficiency. The principle of DDPD-O-OFDM is discussed; and BER and signal-to-noise ratio (SNR) of different DDPD channels are experimentally measured.

Chemometric Quality Assessment of Doxylamine Succinate With Its Degradation Product: Implementation of Two Predictive Models on UV-Spectrophotometric Data of Anti-Emetic Binary Mixture.

The combination of pyridoxine hydrochloride (PYR) and doxylamine succinate (DOX) as an antiemetic binary mixture is used to treat nausea and vomiting during pregnancy. Two validated, accurate, and selective chemometric models were developed to assay binary mixture in the presence of DOX oxidative degradation product (DOX DEG) that could be characterized using LC-MS. Partial least squares (PLS) regression and principal component regression (PCR) were selected for the determination of our binary mixture in presence of degradation. To exhibit a training set of 25 mixtures that had various percentages of tested substances in five level 3 variables, an experimental design was chosen. A set of 18 synthetic mixtures in the concentration range 10.0-50.0 μg/mL, 12.00-20.0 μg/mL, and 6.0-30.0 μg/mL for PYR, DOX, and DOX DEG, respectively, were used in the construction of the calibration models.Then set of seven synthetic mixtures with different concentrations were used in the construction of the validation models. In validation samples with low root mean square error of prediction (RMSEP), the suggested models successfully predicted the concentrations of our drugs. The models developed were evaluated by RMSEP calculation, and the values obtained were 0.341, 0.196, and 0.388 for PYR, DOX, and DOX DEG, respectively, using PLS. While using PCR, RMSEP calculation and the values obtained were 0.400, 0.256, and 0.375 for PYR, DOX, and DOX DEG, respectively. The developed models were validated according to ICH strategies. The corresponding methods are suitable to determine PYR and DOX in pure form, pharmaceutical dosage form, and in the presence of DOX DEG product. The study of drug breakdown pathways is very important nowadays, so even in the presence of degradation and extreme spectral overlapping, the suggested PLS and PCR spectrophotometric approaches were able to identify PYR and DOX.

On resource scheduling and interference mitigation in distributed massive-MIMO wireless orientations via NOMA transmission

The goal of this paper is to evaluate the performance of a proposed resource management approach that mitigates the co-channel interference (CCI) in non-orthogonal multiple access (NOMA) scenarios and maintains their enhanced spectral efficiency in distributed massive multiple input multiple output (d-massive MIMO) configurations as well. In this context, dedicated resource scheduling algorithms (RSAs) in power domain (PD) and frequency domain (FD) are studied in terms of resources’ orthogonality. Specifically, in PD case, adjusted power levels (denoted as PD-NOMA) per subcarrier and mobile terminal (MT) are assigned, while in FD case, the subcarriers are either orthogonal (FD orthogonal multiple access, FD-OMA) or non-orthogonal (FD-NOMA) to each other. The response of the d-massive MIMO system is evaluated statistically via independent Monte Carlo (MC) simulations considering a multicellular multi-user network topology and compared to typical multicellular MIMO configurations. In this framework, a simulation platform is implemented that integrates both the PD and FD RSAs. In PD, both intercell co-channel interference (Inter-CCI) and intracell co-channel interference (Intra-CCI) are modelled analytically in order to estimate the assigned power per subcarrier and MT. In the latter case (Intra-CCI), the worst-case scenario is assumed: a subcarrier can be assigned to multiple MTs (full spectral overlapping) leading to intense Intra-CCI. In FD, two subcarrier allocation approaches are considered: Pseudo-Random or maximum signal-to-noise ratio (MSNR). The simulations in both FD implementations (FD-NOMA, FD-OMA) show that, thanks to the proposed PD-NOMA scheme, each MT requires 1/4 of the maximum available power for downlink transmission. Moreover, in any of the investigated NOMA schemes, despite the intense Intra-CCI, roughly the same number of MTs as in the OMA case can access the network. Therefore, it is straightforward that, even in worst-case scenarios, the NOMA RSAs (i) are wisely exploiting the available resources; (ii) can inherently combat intense Intra-CCI and, in this way, maintain the system’s performance (number of MTs, power savings, resilience against CCI, computation complexity). Finally, it is worth noting that in contrary to typical MIMO configurations, the d-massive MIMO architecture alone can lead up to a 13.63% increase in the system’s capacity (10% maximum allowed blocking probability, 1 tier, 1 subcarrier per MT). In this case, the increased spatial separation that is achieved, along with the exploitation of NOMA RSAs, lead to a decreased CCI (both Intra- and Inter-); hence, SNR is improved and consequently the number of accepted MTs as well.

Polarization-independent near-infrared superabsorption in transition metal dichalcogenide Huygens metasurfaces by degenerate critical coupling

Strong near-infrared absorption of light in semiconducting transition metal dichalcogenides (TMDs) is essential for improving the photocarrier extraction efficiency in optoelectronic devices. Here, we numerically demonstrate that an original TMD Huygens metasurface is specifically designed to overcome the 50% absorptance limit of a subwavelength thin film. The unique metasurface comprising a TMD nanodisk array shows evidence of characteristic Mie resonances including electric and magnetic dipoles. By carefully optimizing the aspect ratio of nanodisks, the extraordinary spectral overlapping of orthogonal electric and magnetic dipole resonances is successfully realized and, thus, enables the super-high absorptance up to 87% in a subwavelength-thin ($\ensuremath{\approx}0.19{\ensuremath{\lambda}}_{0}$) semiconductor structure by degenerate critical coupling at the wavelength of ${\ensuremath{\lambda}}_{0}=903\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$. All numerical results are confirmed by the temporal coupled-mode theory and again via the multipole decomposition method. Importantly, the near-unity absorptance in this TMD Huygens metasurface by degenerate critical coupling not only is tailored throughout the entire near-infrared region but also is both polarization independent and angle insensitive. The absorptance maintaining &gt;80% is observed with the incident angle up to \ifmmode\pm\else\textpm\fi{}10 \ifmmode^\circ\else\textdegree\fi{} at least. Our findings are not only of fundamental interest but could also offer a platform for TMD-based high-speed photodetecting, energy harvesting, and thermal emission.

Application of Fourier transform-based algorithms to resolve spectral overlapping for UV spectrophotometric co-assay of spiramycin and metronidazole in tablets

Fourier transform-based algorithms were investigated to resolve UV spectral overlapping of spiramycin and metronidazole in binary mixtures. UV spectra and ratio spectra were both subjected to fast Fourier transform-based first-order differentiation and discrete Fourier transform {i.e. using trigonometric functions such as sin xi – sin (xi + 450), cos xi + cos (xi + 450), sin 2xi – sin 2(xi + 450), cos 2xi + cos 2(xi + 450), sin xi – sin (xi + 600), cos xi + cos (xi + 600)} that followed by 3 passes of 17-point triangular smooth. Such signal transforms generated linear calibration graphs for either drug in the concentration range of 6.25 – 25 mg/L with R2 > 0.990. In comparison with the RP-HPLC reference method, the developed UV spectrophotometric methods had no significant difference in terms of accuracy and precision (p > 0.05) when quantifying spiramycin and metronidazole in their coated tablets. They are suggested as analytical quality control methods for their being environmentally friendly, technically simple, quick and economic.

Dy3+/Er3+/Tm3+ tri-doped tellurite glass with enhanced broadband mid-infrared emission

Dy3+/Er3+/Tm3+ tri-doped tellurite glass was synthesized using melt-quenching technology, and the enhanced broadband mid-infrared band luminescence around 3.0 µm was reported for the first time under the excitation of 808 nm laser diode. The broadband mid-infrared luminescence observed in the range of 2600–3200 nm comes from the spectral overlapping of Er3+:2.7 µm and Dy3+:2.84 µm emissions, while the significant enhancement is mainly contributed by the energy transfers from Er3+:4I13/2 to Dy3+:6H11/2, Er3+:4I13/2 to Tm3+:3F4 and Tm3+:3F4 to Dy3+:6H11/2 levels. Compared with Dy3+ single-doped tellurite glass, the peak intensity of this mid-infrared band luminescence in tellurite glass tri-doped with 0.5 mol% Dy2O3, 0.5 mol% Er2O3 and 1.0 mol% Tm2O3 increases by about 214%. Additionally, the spectroscopic properties of Dy3+ ions were investigated by applying Judd-Ofelt theory and the energy transfer mechanism was analyzed to understand the enhanced broadband luminescence phenomena. The obtained results reveal that Dy3+/Er3+/Tm3+ tri-doped tellurite glass is a promising lasing medium for 3.0 µm band mid-infrared broadband photonic devices.

Dual-readout fluorescence quenching immunochromatographic test strips for highly sensitive simultaneous detection of chloramphenicol and amantadine based on gold nanoparticle-triggered photoluminescent nanoswitch control

Herein, a novel fluorescence quenching immunochromatographic test strip (FQICTS) for simultaneous detection of chloramphenicol (CAP) and amantadine (AMD) was developed on the basis of inner filter effect (IFE), with the combination of gold nanoparticles (AuNPs) and highly luminescent green-emitting gold nanoclusters (AuNCs) as the IFE quencher/donor pair. The AuNPs could quench the excitation light and emission light of AuNCs and achieve a high IFE efficiency due to dual spectral overlapping. Under optimal conditions, the “turn-on” mode of the AuNCs-based dual-readout FQICTS showed good linearity for CAP detection in chicken samples from 0.05 ng/g to 10 ng/g, with a limit of detection (LOD) of 0.043 ng/g. The linear range of AMD is 0.5–50 ng/g, with LOD of 0.45 ng/g. The visual LODs of CAP and AMD in “turn-on” mode were 200 and 10 times lower than that in “turn-off” mode, respectively. The “turn-on” mode of FQICTS showed high recovery for detecting CAP (82.5–94.5%) and AMD (81.9–110.7%) spiked into chicken samples. The performance and practicability of the established method were verified with commercial enzyme-immunoassay kits, and good correlations were observed. Overall, the newly developed AuNCs-based dual-readout FQICTS is a promising on-site screening tool for rapid, high-sensitivity detection of multiple food contaminants in practical applications.

Combination of multi-focus Raman spectroscopy and compressive sensing for parallel monitoring of single-cell dynamics

To overcome the low efficiency of conventional confocal Raman spectroscopy, many efforts have been devoted to parallelizing the Raman excitation and acquisition, in which the scattering from multiple foci is projected onto different locations on a spectrometer’s CCD, along either its vertical, horizontal dimension, or even both. While the latter projection scheme relieves the limitation on the row numbers of the CCD, the spectra of multiple foci are recorded in one spectral channel, resulting in spectral overlapping. Here, we developed a method under a compressive sensing framework to demultiplex the superimposed spectra of multiple cells during their dynamic processes. Unlike the previous methods which ignore the information connection between the spectra of the cells recorded at different time, the proposed method utilizes a prior that a cell’s spectra acquired at different time have the same sparsity structure in their principal components. Rather than independently demultiplexing the mixed spectra at the individual time intervals, the method demultiplexes the whole spectral sequence acquired continuously during the dynamic process. By penalizing the sparsity combined from all time intervals, the collaborative optimization of the inversion problem gave more accurate recovery results. The performances of the method were substantiated by a 1D Raman tweezers array, which monitored the germination of multiple bacterial spores. The method can be extended to the monitoring of many living cells randomly scattering on a coverslip, and has a potential to improve the throughput by a few orders.

Analysis of the ternary antiretroviral therapy dolutegravir, lamivudine and abacavir using UV spectrophotometry and chemometric tools

Herein, a simple spectrophotometric method coupled with chemometric techniques i.e. partial least square (PLS) and genetic algorithm (GA) were utilized for the simultaneous determination of the vital ternary antiretroviral therapy dolutegravir (DTG), lamivudine (LMV), and abacavir (ACV) in their combined dosage form. Calibration (25 samples) and validation (13 samples) sets were prepared for these drugs at different concentrations via implementing partial factorial experimental designs. The zero order UV spectra of calibration and validation sets were measured and then subjected for further chemometric analysis. Partial least squares with/without variable selection procedures i.e. genetic algorithm (GA) were utilized to untangle the UV spectral overlapping of these mixtures. Cross-validation and external validation methods were applied to compare the performance of these chemometric techniques in terms of accuracy and predictive abilities. It was found that six latent variables were optimum for modelling DTG, four latent variables for modelling LMV and three latent variables for modelling ACV. Although, good recoveries with prompt predictive ability were attained by these PLS, GA-PLS showed better analytical performance owing to its capability to remove redundant variables i.e. the number of absorbance variables have been reduced to about 21–29%. The proposed chemometric methods can be reliably applied for simultaneous determination of DTG, LMV, and ACV in their laboratory prepared mixtures and pharmaceutical preparation posing these chemometric methods as worthy and substantial analytical tools in in-process testing and quality control analysis of many antiretroviral pharmaceutical preparations.

Spectral overlap and temporal avoidance in a tropical savannah frog community

Vocalizing animals often occur in complex acoustic environments where there is a high chance of acoustic interference from co-occurring species with spectrally overlapping vocalizations. Acoustic interference impedes detection and discrimination of signals, and may ultimately reduce fitness. The aim of this study was to determine the relationship between spectral overlap and temporal overlap in a tropical savannah frog community. We predicted that species pairs that overlap spectrally would behaviourally respond to one another by avoiding calling at the same time, to minimize acoustic interference. We determined the calling activity of 14 frog species at four locations across 4 months during peak breeding season. We then determined the difference between observed and expected temporal overlap for all species pairs as a function of spectral overlap at three temporal scales (night-minute-call). There was potential for acoustic interference between many of the species studied with the calls of up to half of the species pairs at each site overlapping spectrally. There was no relationship between spectral overlap and observed–expected temporal overlap at either the night or minute level. Instead, calling activity was aggregated at both the night and minute level. Evidence of a negative relationship between spectral overlap and temporal overlap was found at the call level, with species pairs with greater mean spectral overlap calling together less frequently than expected. The observed aggregated calling at the night and minute level suggest that at gross timescales, factors other than avoiding spectral overlap are driving calling activity in tropical savannah frog communities. The call level avoidance found in this study may be sufficient for spectrally overlapping species pairs to avoid the negative effects of acoustic interference, allowing them to call during the same nights and at similar times to take advantage of favourable environmental conditions.

Fe3O4@PDA@PANI core–shell nanocomposites as a new adsorbent for simultaneous preconcentration of Tartrazine and Sunset Yellow by ultrasonic-assisted dispersive micro solid-phase extraction

In this research, novel magnetic Fe3O4@PDA@PANI core–shell nanoparticles were designed and fabricated as an efficient adsorbent in the service of ultrasound-assisted dispersive micro-solid phase extraction for simultaneous preconcentration of Sunset Yellow (SY) and Tartrazine (Tar) before UV–Vis spectrophotometric detection. This adsorbent was fully characterized by Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive X-ray (EDX) analysis. To overcome the spectral overlapping of SY and Tar dyes, the derivative spectrophotometric method was successfully used for the simultaneous detection of dyes in their binary solutions. The operating parameters affecting preconcentration efficiency and spectrophotometric determination were optimized. Under optimal conditions, the limit of detections (LOD) was obtained 0.2 and 0.5 ng mL−1 for SY and Tar, respectively. The adsorption capacity and reusability of core–shell nanoparticles were significant. The satisfactory results of analysis of a few real samples indicate that the method is very favored in the analysis of various complex matrices.

Estimated ECG Subtraction method for removing ECG artifacts in esophageal recordings of diaphragm EMG

The accuracy of diaphragm electromyogram (EMGdi) derived parameters, as used in critically ill intensive care unit (ICU) patients, can be compromised due to electrocardiographic (ECG) interference in the EMGdi signal. Removal of ECG contamination from the esophageal recordings of the EMGdi is challenging due to spectral overlapping of EMG and ECG signals and because of variability in ECG shape and amplitude. Therefore, we designed an Estimated ECG Subtraction (EES) method, based on three steps: (1) identification of the timing of the ECG artifact without an ECG reference channel, (2) estimation of the normalized ECG, considering the EMGdi as noise, and (3) subtraction of the denormalized ECG estimate from the EMGdi recordings. We evaluated the EES method against the use of a single wavelet-based adaptive filter. Using EMGdi signals of ten ICU patients and simulated contaminated EMG, we demonstrated that the EES method yields uncontaminated EMGdi, and showed that it is more effective than a wavelet-based adaptive filter only. Implementation of this technique may offer means to improve diaphragm activity monitoring and control in clinical practice.

Ultraviolet Spectroscopic Detection of Nitrate and Nitrite in Seawater Simultaneously Based on Partial Least Squares.

A direct, reagent-free, ultraviolet spectroscopic method for the simultaneous determination of nitrate (NO3−), nitrite (NO2−), and salinity in seawater is presented. The method is based on measuring the absorption spectra of the raw seawater range of 200–300 nm, combined with partial least squares (PLS) regression for resolving the spectral overlapping of NO3−, NO2−, and sea salt (or salinity). The interference from chromophoric dissolved organic matter (CDOM) UV absorbance was reduced according to its exponential relationship between 275 and 295 nm. The results of the cross-validation of calibration and the prediction sets were used to select the number of factors (4 for NO3−, NO2−, and salinity) and to optimize the wavelength range (215–240 nm) with a 1 nm wavelength interval. The linear relationship between the predicted and the actual values of NO3−, NO2−, salinity, and the recovery of spiked water samples suggest that the proposed PLS model can be a valuable alternative method to the wet chemical methods. Due to its simplicity and fast response, the proposed PLS model can be used as an algorithm for building nitrate and nitrite sensors. The comparison study of PLS and a classic least squares (CLS) model shows both PLS and CLS can give satisfactory results for predicting NO3− and salinity. However, for NO2− in some samples, PLS is superior to CLS, which may be due to the interference from unknown substances not included in the CLS algorithm. The proposed method was applied to the analysis of NO3−, NO2−, and salinity in the Changjiang (Yangtze River) estuary water samples and the results are comparable with that determined by the colorimetric Griess assay.

Enhanced ultra-wide NIR fluorescence in tellurite glass doped with Er3+-Tm3+-Nd3+-Ag NPs

Tellurite glasses with combination of Er3+/Tm3+/Nd3+ ions and silver nanoparticles (Ag NPs) were prepared by using single-step melt-quenching technology, and the enhanced effect of Ag NPs on the ultra-broadband near-infrared (NIR) fluorescence was studied. Under the 808 nm LD excitation, two ultra-broadband NIR fluorescence of 1300–1600 nm and 1600–2100 nm underwent an obvious enhancement of about 52% compared to the tri-doping tellurite glass free of Ag NPs. The intensified local electric field induced by Ag NPs together with the energy transfer from Ag species to doped ions is responsible for this enhancement. The enhanced ultra-broadband NIR fluorescence of 1300–1600 nm with the full width at half maximum (FWHM) of 230 nm, originating from the spectral overlapping of 1.34 µm (4F3/2→4I13/2 of Nd3+), 1.47 µm (3H4→3F4 of Tm3+) and 1.53 µm (4I13/2→4I15/2 of Er3+) three bands, is promising in developing new ultra-broadband photonic devices such as fiber amplifiers and tunable lasers.

Comparative study of novel green UV-spectrophotometric platforms for simultaneous rapid analysis of flumethasone pivalate and clioquinol in their combined formulation

Flumethasone pivalate (FP) and clioquinol (CL) formulation was developed as a prodigious remedy to cure the external ear inflammatory disorders. So, the current research introduces five smart and novel UV-spectrophotometric platforms relying on minimal mathematical manipulation steps for simultaneous green analysis of FP and CL with no preliminary separation in their formulation that suffered from the high difference of their ratio and severe spectral overlapping. These platforms involved dual-wavelength, first derivative ratio, Fourier self-deconvolution, area under the curve, and bivariate methods. The suggested platform’ linearity was observed over the concentration range of 3–42 µg/ml for FP and 1.5–8 µg/ml for CL. All suggested platforms were validated according to ICH recommendations regarding accuracy, precision, repeatability, and selectivity producing satisfactory results within the accepted limits. These platforms were represented as rapid, green, and cheap alternatives to the reported chromatographic method due to lower solvent consumption and waste generation. Furthermore, they improved the determination sensitivity of the studied drugs and enhanced the recorded data signals or its spectral resolution by the newly introduced Fourier self-deconvoluted method. The statistical comparison between the results of the suggested platforms with each other and with those of the reported method showed no significant differences between them.

Dielectric Huygens’ metasurfaces with diverse functionalities in the range from near-UV to deep-UV

Despite of great endeavors for extending the spectral range, there is still absent Huygens’ metasurfaces operating in the ultraviolet (UV). This work reports highly efficient dielectric Huygens’ metasurfaces in the spectral range from near-UV to deep-UV, which are made of dielectric materials with moderate refractive indices such as diamond and lithium tantalate. They can exhibit versatile functionalities in the UV range owing to their inherent physical nature. By employing their high transmittance and full 2π controllability of phase, we numerically demonstrate non-diffracting Bessel beam generation in the UV with a near-unity efficiency and compression of a chirped UV pulse with a duration of 88 fs down to 49 fs, as examples. In particular, we reveal that the dielectric Huygens’ metasurfaces can generate second harmonic radiations with high efficiency, for the first time to the best of our knowledge. Due to the spectral overlapping of the electric and magnetic resonances at the same wavelength, the dielectric Huygens’ metasurfaces generate highly enhanced local field in the nanodisks, enabling to obtain high nonlinear generation efficiency. The results show that vacuum UV radiation at 162 nm can be generated with efficiency in the order of 10−2% in transmission regime from the Huygens’ metasurface of LiTaO 3 nanodisk array. Diverse functionalities of dielectric Huygens’ metasurfaces in the UV region proposed in this work will find important applications for UV photonics.

Broadband mid-infrared emission in Dy3+/Er3+ co-doped tellurite glass

Broadband mid-infrared luminescence in Dy3+/Er3+ co-doped tellurite glasses was reported in this work. The doped tellurite glasses were prepared using conventional melt-quenching technique, and their structural property and thermal stability were analyzed by the X-ray diffraction (XRD) pattern, Raman spectrum and differential scanning calorimeter (DSC) curve. Judd-Ofelt theory was applied to the absorption spectra to evaluate the spectroscopic properties like radiative transition probability, branching ratio and radiative lifetime of Dy3+ and Er3+ ions. The photoluminescence measured under excitation of 808 nm laser diode (LD) displayed an ultra-broadband mid-infrared band emission with full width at half maximum (FWHM) of ~358 nm in tellurite glass with appropriate amount of Dy3+-Er3+ combination. This broadband mid-infrared band emission located in the range of 2550–3200 nm and originated from the spectral overlapping of 2.85 μm band emission of Dy3+:6H13/2 → 6H15/2 transition and 2.7 μm band one of Er3+:4I11/2 → 4I13/2 transition. Furthermore, the time resolved fluorescence decay behavior demonstrated the existence of energy transfer between Dy3+ and Er3+ ions which is responsible for the broadband luminescence, and the energy transfer efficiency was estimated. The present results indicate that tellurite glass co-doped with Dy3+-Er3+ ions is promising for applications in mid-infrared band luminescent sources and tunable lasers.