Spectral Range Research Articles

6.7–8.1 µm tunable single-frequency difference frequency generation in ZGP for high-resolution spectroscopy

Difference frequency generation (DFG) based tunable single-frequency mid-infrared (MIR) light sources are desirable for high-resolution spectroscopy, sensing, and imaging. In this work, we demonstrate a continuous-wave (CW) single-frequency DFG in a ZnGeP2 (ZGP) crystal driven by all-fiber near-infrared (NIR) fiber lasers, for the first time to our knowledge. The all-fiber NIR laser sources consist of a 1.5 µm erbium-doped fiber amplifier seeded by a CW tunable fast scanning single-frequency laser and a 1.9 µm CW tunable single-frequency thulium-doped fiber laser. Taking advantage of the high nonlinear coefficient and large birefringence of the ZGP crystal, single-frequency DFG in ZGP achieves a broad spectral tuning range from 6.7 to 8.1 µm, with an output power at the 10 µW level. Precise detection of C2H2 gas by continuously scanning the DFG source across a spectral range of 1.1 THz (∼34 cm−1) is also presented, highlighting the potential of the tunable DFG source for high-resolution optical spectroscopy applications. We anticipate this work will provide what we believe to be a new platform for spectroscopy in the molecular fingerprint spectral region.

Multispectral multiplexed confocal FLIM for live cell imaging

Abstract Spectrally resolved fluorescence lifetime imaging with high spatial precision offers comprehensive information on species localization and behavior. It is challenging to resolve weak fluorescence signals in multiple dimensions (spatial, spectral, and temporal) at high frame rates, especially in dynamic live cell processes, as photobleaching and phototoxicity limit acceptable photon count rates. We developed a multiplexed confocal FLIM technique, which uses a prism-based imaging spectrometer to separate a 10x10 array of confocal foci into their spectral components. This allows the sampling of the spectra by a time-resolved image sensor to produce a multispectral time-resolved data set used for generating multispectral lifetime images. This system captures 300x300 pixel fluorescence lifetime images containing 12 unique spectral bands covering a 450-700 nm spectral range in 1.8 seconds of exposure. Its performance was demonstrated in fixed stained samples and in multispectral imaging of FLIM-FRET in live cells.

Systematic comparison of fluorescence imaging in the near-infrared and shortwave-infrared spectral range using clinical tumor samples containing cetuximab-IRDye800CW

Systematic comparison of fluorescence imaging in the near-infrared and shortwave-infrared spectral range using clinical tumor samples containing cetuximab-IRDye800CW

Probing coherence properties of shallow implanted NV snsembles under different oxygen terminations

Abstract Nitrogen vacancy (NV) color centers in diamond have shown great potential for various applications in quantum technology due to their long coherence times, high sensitivity to magnetic fields and atomic scale resolution. However, one major challenge in utilizing near surface NV centers is the decoherence caused by spins and charges fluctuating on the surface, which affects the spin properties of the sensors. To reduce the induced noise, various oxygen surface treatments such as low power oxygen plasma treatment and annealing under oxygen atmosphere have been explored to terminate the diamond surface and reduce its impact on NV coherence. We showed that the NV center's coherence time can be enhanced up to a factor of 3 over a large spectral range of noise. Double electron electron resonance (DEER) measurements revealed an extra source of decoherence, scaling similarly as the P1 spin bath. The improvement in coherence times is accompanied with an increase in measured ketone/ether content and reduction of sp2 signal in X-ray photoelectron spectroscopy (XPS) measurements. Finally we compared the performance of different NV ensembles and surface treatments for sensing external proton spins. The oxygen annealing is an effective procedure of enhancing the spin coherence times and reducing broad band spin noise experienced by shallow implanted ensemble NV centers in diamond.

Unleashing the nonlinear optical response of layered vanadium diselenide towards the deep mid-infrared regime

Broadband nonlinear optical materials towards the deep mid-infrared regime are highly required in medical diagnostics, environmental pollution monitoring, etc. Here, we report the ultra-broadband nonlinear optical absorption behavior of the layered vanadium diselenide (VSe2) towards deep mid-infrared regime experimentally. The layered VSe2 prepared by the liquid-phase exfoliation method exhibits broadband and wavelength-dependent nonlinear saturable absorption and a large modulation depth of over 8% in the 3-10 µm spectral range. By utilizing the layered VSe2 for optical modulation, stable nanosecond pulse with a low Q-switched threshold has been delivered successfully from an erbium-doped ZBLAN fiber laser. The experimental findings can deepen the understanding of the nonlinear optical response of the transition metal dichalcogenides towards the deep mid-infrared regime, and may make inroads for the advancement of mid-IR optoelectronic devices.

Determination of Optical and Structural Parameters of Thin Films with Differently Rough Boundaries

The optical characterization of non-absorbing, homogeneous, isotropic polymer-like thin films with correlated, differently rough boundaries is essential in optimizing their performance in various applications. A central aim of this study is to derive the general formulae necessary for the characterization of such films. The applicability of this theory is illustrated through the characterization of a polymer-like thin film deposited by plasma-enhanced chemical vapor deposition onto a silicon substrate with a randomly rough surface, focusing on the analysis of its rough boundaries over a wide range of spatial frequencies. The method is based on processing experimental data obtained using variable-angle spectroscopic ellipsometry and spectroscopic reflectometry. The transition layer is considered at the lower boundary of the polymer-like thin film. The spectral dependencies of the optical constants of the polymer-like thin film and the transition layer are determined using the Campi–Coriasso dispersion model. The reflectance data are processed using a combination of Rayleigh–Rice theory and scalar diffraction theory in the near-infrared and visible spectral ranges, while scalar diffraction theory is used for the processing of reflectance data within the ultraviolet range. Rayleigh–Rice theory alone is sufficient for the processing of the ellipsometric data across the entire spectral range. We accurately determine the thicknesses of the polymer-like thin film and the transition layer, as well as the roughness parameters of both boundaries, with the root mean square (rms) values cross-validated using atomic force microscopy. Notably, the rms values derived from optical measurements and atomic force microscopy show excellent agreement. These findings confirm the reliability of the optical method for the detailed characterization of thin films with differently rough boundaries, supporting the applicability of the proposed method in high-precision film analysis.

Influence of polymer solution parameters on optical fiber Fabry-Perot polymer cavities

Abstract Optical fiber polymer-based Fabry-Perot sensors are commonly utilized to detect and measure a wide range of physical and chemical properties. By dipping the cleaved end of a single mode fiber into the polymer solution, a cavity is formed at the end facet of the fiber, as the solution effectively bonds to the fiber surface. The cavity serves as a sensing structure for the interaction with the analyte, ultimately determining the sensor’s sensitivity. Maintaining consistent thickness of the FP cavities is of utmost importance for the coating mechanism, as it directly impacts the sensitivity of the FP sensor. The main aim of this study is to assess and establish a technique that can effectively generate a cavity at the end facet of a fiber. A simulation study is conducted to examine the influence of variations in polymer solution characteristics on the cavity fabrication. Our experimental work involved creating polymer cavities on varying the polymer viscosity on the end facet of optical fibers. Furthermore, the suitability of this proposed approach has been assessed on a range of polymers, examining the fluctuations in the free spectral range of the fabricated FP cavities. The findings of this research highlight the possibility of achieving a repeatable coating on the end facet of fiber, irrespective of the polymer used.

Polypyrrole-bismuth tungstate/polypyrrole core-shell for optoelectronic devices exhibiting Schottky photodiode behavior.

A polypyrrole-bismuth tungstate (Ppy-Bi2WO6) core-shell nanocomposite (n-type material) has been developed on a layered Ppy (p-type) base as an efficient light-capturing material exhibiting photodiode behavior. This device demonstrates promising sensitivity for light sensing and captures across a broad spectral range, from near IR to UV. The Bi2WO6/Ppy nanocomposite boasts an optimal bandgap of 2.0eV, compared to 3.4eV for Ppy and 2.5eV for Bi2WO6. The crystalline size of the core-shell composite is approximately 21nm, emphasizing its photon absorption capabilities. The composite particles, around 100nm in length, feature a highly porous morphology that effectively traps incident photons. The performance of this optoelectronic device is evaluated using current density (J) measurements under light (Jph) and dark (Jo) conditions. In darkness, the n-p type semiconductor exhibits limited current with a Jo of -0.22mA cm-2 at 2.0V. When exposed to white light, the Ppy- Bi2WO6/Ppy device generates hot electrons, achieving a Jph value of 1.1mA/cm-2 at 2.0V. It shows a superior responsivity (R) of 6.6mA/W at 340nm, gradually decreasing to 6.3mA/W at 440nm and 4.2mA/W at 540nm, indicating high sensitivity across the UV-Vis spectrum. At 730nm, the R-value is 2.6mA/W, highlighting its sensitivity in the near IR region. Additionally, at 340nm, the device achieves a detectivity (D) value of 0.15 × 10¹⁰ Jones, which decreases with longer wavelengths to 0.14 × 10¹⁰ Jones at 440nm, 0.9 × 10⁹ Jones at 540nm, and 0.63 × 10⁹ Jones at 730nm. With its great stability, low cost, easy fabrication, and potential for mass production, this optoelectronic light sensor and photodiode device holds significant promise for industrial applications as a highly effective optoelectronic device.

Influence of polarization on demodulation methods for determining the SRI value for a single TFBG and an orthogonal grating system

This paper presents a comparison of the spectra of single and cascade of two tilted fiber Bragg grating (TFBG) sensors. These sensors are characterized by high sensitivity to the refractive index. The disadvantage of a single TFBG is cross-sensitivity to changes in the polarization of the light introduced to the sensor, which is visible both when analyzing individual modes and when analyzing a wide spectral range with global demodulation algorithms. In response, a cascade structure was created consisting of a set of two TFBGs connected in series with 90 degrees of mutual rotation between them. This work presents a comparison of the polarization cross-sensitivity of sensor spectral demodulation algorithms for measuring the surrounding refractive index (SRI). While maintaining the high accuracy of the SRI measurement typical of TFBG gratings, a cascade of two such gratings properly oriented toward each other allows for a significant reduction in the sensitivity of the SRI measurement to polarization changes. Importantly, the reduction in the polarization cross-sensitivity is significantly greater for the demodulation methods that determine the cutoff wavelength shift; owing to this, a perpendicular TFBG(P-TFBG) measurement system without polarization control remains highly reliable. The application of the proposed P-TFBG system also allows greater SRI sensitivity to be obtained for a single tilted grating with the same tilt angle.

Fu's subcutaneous needling for non-acute idiopathic facial paralysis : a randomized controlled trial

To observe the effect of Fu's subcutaneous needling in the treatment of non-acute idiopathic facial paralysis and its effect on serum levels of nitric oxide (NO) and endothelin (ET). A total of 76 patients with non-acute idiopathic facial paralysis were randomly divided into an observation group (38 cases, 2 cases dropped out) and a control group (38 cases, 2 cases dropped out). The patients in the control group received basic treatment (mecobalamin tablets orally, specific electromagnetic spectrum irradiation, facial muscle rehabilitation training). The patients in the observation group were treated with Fu's subcutaneous needling on the basis of the control group. The needling points included brachioradialis muscle, sternocleidomastoid muscle, trapezius muscle, etc., and the needling was inserted around the affected muscle, and the reperfusion activity was carried out at the same time, once every other day, 3 times a week. Both groups were treated for 4 weeks. The House-Brackmann (H-B) grade and H-B symptom score were observed before treatment, after 2 and 4 weeks of treatment in the two groups. The facial disability index (FDI) score [including physical function (FDIP) score and social life function (FDIS) score] and the serum levels of NO and ET were compared before and after 4 weeks of treatment in the two groups. The clinical effect and safety of the two groups were assessed. After 2 and 4 weeks of treatment, the H-B grade of the two groups was lower than that before treatment, and the H-B symptom scores were higher than those before treatment (P<0.001, P<0.05); the H-B grade of the observation group was lower than that of the control group, and the H-B symptom score was higher than that of the control group (P<0.01, P<0.05). After 4 weeks of treatment, the FDIP scores of the two groups were higher than those before treatment, and the FDIS scores were lower than those before treatment (P<0.05 ); the FDIP score of the observation group was higher than that of the control group, and the FDIS score was lower than that of the control group (P<0.05). After 4 weeks of treatment, the serum level of NO in the observation group was higher than that before treatment, and the serum level of ET was lower than that before treatment (P<0.05); the increase of serum level of NO and the decrease of serum level of ET in the observation group were greater than those in the control group (P<0.05). The cure rate of the observation group was 55.6% (20/36), which was higher than 22.2% (8/36) of the control group (P<0.05). There were no serious adverse reactions in both groups. Fu's subcutaneous needling combined with basic treatment can effectively improve the motor function of facial muscles in patients with non-acute idiopathic facial paralysis, which may be related to the regulation of serum NO and ET levels.

THE COGNITIVE ELECTRONIC WARFARE IN THE AGE OF ARTIFICIAL INTELLIGENCE

Collecting and acting on data has increased the military’s dependency on the electromagnetic spectrum (EMS). Electronic Warfare (EW) controls the Electromagnetic Spectrum (EMS) in order to detect, analyze, and track potential threats. EW provides situational awareness for diplomatic insights, defensive measures and offensive options for each country. EW enables Joint Electromagnetic Spectrum Operations (JEMSO). In the EM Operation Environment, the armed forces exploit, protect and attack. More advanced EW can identify, intercept and decode the adversaries’ Data. It can also project directed energy to disrupt enemy operations, reducing the impact of conflicts or preventing some armed conflicts before they begin.Applying cognitive systems to EW helps the army personnel identify patterns and improve the systems, as well as anticipating the COA. Cognitive Electronic Warfare systems interpret a large amount of data from a range of vast sources to provide hypotheses for action plans. Combining human strategies with computer input ensures the success of Cognitive EW approach. Leaving data collection and probability calculations to computers let humans time to think, to be creative and to use their intuiton in order to find the best solutions.

Terahertz time-domain investigation of atacamite: Spectral analysis and theoretical insights for cultural heritage applications

Spectroscopic methods based on terahertz (THz) radiation can represent an innovative approach in the Cultural Heritage field. Specifically, contemporary and historical pigments can exhibit unique fingerprints. However, despite the high selectiveness of terahertz technique, the origin of spectral characteristics is not often known. In this work, the characteristic terahertz-time-domain spectroscopy spectrum of atacamite is reported in the spectral range 0.1–3.7 THz along with ab initio calculation of lattice dynamics to assess the nature of experimental features. The obtained results enable the acquisition of reliable new data in Heritage sciences, which is essential for developing accurate reference pigment databases.

Comparison of a Quantum Cascade Laser and an Interband Cascade Laser for the Detection of Stable Carbon Dioxide Isotopes Using Tunable Laser Absorption Spectroscopy.

Quantum cascade lasers (QCLs) and interband cascade lasers (ICLs) are widely used as light sources in tunable laser absorption spectroscopy because they emit in the mid-infrared region where many strong and characteristic absorption bands are present. In this paper, we compare the performance of these lasers emitting at about 2310.1 cm-1 to determine an optimal light source for detecting isotopic ratios of carbon dioxide (CO2). Our results show that the QCL has a higher relative intensity noise of up to 15 dBc/Hz compared to the ICL over the entire measured frequency range. In addition, it has a higher frequency fluctuation. However, the maximum tuning range of the QCL is up to 5.2 cm-1 compared to up to 3.8 cm-1 for the ICL. Both lasers lose more than half of their tuning range when the tuning rate is increased to 10 kHz. When measuring the isotope ratio of CO2, an uncertainty in the value of ‰ was achieved with the ICL and of ‰ with the QCL, both at an integration time of 0.2 s. In summary, the QCL is more appropriate for applications that require a larger spectral tuning range, such as the measurement of a complex gas mixture, while the ICL has an excellent signal-to-noise ratio and is therefore better suited for applications that require higher precision.

CsPbBr3 perovskite quantum dots/p-GaN heterojunction for ultraviolet-visible spectrum photodetectors

All-inorganic perovskites have attracted increasing attention because of their strong environmental stability and excellent photoelectric properties. However, the limited spectral response range of perovskite photodetectors restricts them in practical applications. In this work, an ultraviolet–visible photodetector with a wide spectral response and a high responsivity was prepared by constructing a CsPbBr3 quantum dots (QDs)/p-GaN heterojunction. The type-II energy band alignment formed by the heterojunction is conducive to the transport of photogenerated carriers, resulting in a high responsivity. Under certain conditions, the device can obtain responsivity values of 5 A/W and 850 mA/W under 350 and 725 nm illumination, respectively, which are comparable to those of other perovskite-based photodetectors. In addition, the photoresponse mechanism of the device is revealed through first-principles calculations of the heterojunction and the device. The enhanced light absorption of the heterojunction and the special band bending under different bias voltages improve the photoelectric performance of the device. This work can provide valuable insights into high-performance photodetectors based on all-inorganic perovskite QDs heterojunctions in terms of band regulation and device performance improvement.

Multi-octave two-color soliton frequency comb in integrated chalcogenide microresonators.

Mid-infrared (MIR) Kerr microcombs are of significant interest for portable dual-comb spectroscopy and precision molecular sensing due to strong molecular vibrational absorption in the MIR band. However, achieving a compact, octave-spanning MIR Kerr microcomb remains a challenge due to the lack of suitable MIR photonic materials for the core and cladding of integrated devices and appropriate MIR continuous-wave (CW) pump lasers. Here, we propose a novel slot concentric dual-ring (SCDR) microresonator based on an integrated chalcogenide glass chip, which offers excellent transmission performance and flexible dispersion engineering in the MIR band. This device achieves both phase-matching and group velocity matching in two separated anomalous dispersion regions, enabling phase-locked, two-color solitons in the MIR region with a commercial 2-μm CW laser as the pump source. Moreover, the spectral locking of the two-color soliton enhances pump wavelength selectivity, providing precise control over soliton dynamics. By leveraging the dispersion characteristics of the SCDR microresonator, we have demonstrated a multi-octave-spanning, two-color soliton microcomb, covering a spectral range from 1156.07 to 5054.95nm (200 THz) at a -40dB level, highlighting the versatility and broad applicability of our approach. And the proposed multi-octave MIR frequency comb is relevant for applications such as dual-comb spectroscopy and trace-gas sensing.

Photocatalytic Reactions over TiO2-Based Interfacial Charge Transfer Complexes

The present review is related to the novel approach for improvement of the optical properties of wide bandgap metal oxides, in particular TiO2, based on the formation of the inorganic–organic hybrids that display absorption in the visible spectral range due to the formation of interfacial charge transfer (ICT) complexes. We outlined the property requirements of TiO2-based ICT complexes for efficient photo-induced catalytic reactions, emphasizing the simplicity of the synthetic procedure, the possibility of the fine-tuning of the optical properties supported by the density functional theory (DFT) calculations, and the formation of a covalent linkage between the inorganic and organic components of hybrids, i.e., the nature of the interface. In addition, this study provides a comprehensive insight into the potential applications of TiO2-based ICT complexes in photo-driven catalytic reactions (water splitting and degradation of organic molecules), including the identification of the reactive species that participate in photocatalytic reactions by the spin-trapping electron paramagnetic resonance (EPR) technique. Considering the practically limitless number of combinations between the inorganic and organic components capable of forming oxide-based ICT complexes and with the knowledge that this research area is unexplored, we are confident it is worth studying, and we emphasized some further perspectives.

Four-level diffractive photon sieves by deep-UV femtosecond laser ablation

A growing demand for complex light manipulation and miniaturization of optics necessitates advanced optical elements, operating on light diffraction phenomena, capable not only of reshaping the intensity distribution but also integrating many optical functions in a compact, durable device. The prevailing fabrication methods for these elements often involve multi-step lithographic processes. In contrast, direct laser ablation offers a single-step, cost-effective, and maskless alternative. However, using solid-state laser systems’ fundamental wavelength (in the IR range) for ablation lacks the precise depth control required for multi-level diffractive optical element fabrication. In this paper, we present the first experimental proof that femtosecond direct laser ablation in the UV spectral range is a reliable method for fabricating diffractive optical elements. We demonstrate the high-quality production of compact photon sieve focusing elements with the shortest focal length ever reported at 9 mm. Furthermore, we report an efficiency of 3.3%, which, to our knowledge, is the highest for elements with such a small focal length and not far from the theoretical efficiency limit of 4.46% (considering perfect cylindrical ablated pits). Moreover, our fabricated elements focus light to a 2.3% smaller focal spot if compared to the refractive lens with the same parameters. This fabrication method shows great promise for advanced applications that require precise depth control in wide band gap materials, such as the fused quartz used in this study.

A Quad‐Port MIMO Antenna With Improved Isolation Developed by Colored Resin Fiber Material for Wideband Applications

ABSTRACTThe article explores a quad‐port compact (56 × 56 × 1.5 mm3) multiple‐input multiple‐output (MIMO) antenna developed on a colored resin fiber material encompassing enhanced isolation for wideband applications. The design antenna configuration incorporates four ground stubs positioned among antenna pairs on the upper section of the substrate and eight rectangular‐shaped ground slots to enhance antenna isolation. The antenna functions over a broad spectral range from 4.21 to 10.95 GHz, providing coverage for WLAN (5.15–5.35 GHz/5.725–5.825 GHz), C band uplink (5.925–6.425 GHz), downlink defense (7.2–7.7 GHz), and ITU band (8–8.5 GHz), with 88.91% fractional bandwidth. The antenna design ensures exceptional isolation, exceeding 21 dB among orthogonal antennas and 25 dB between oppositely placed antennas across the entire functioning bandwidth. Across the working band, the antenna showcases favorable diversity characteristics, including a lower envelope correlation coefficient (ECC &lt; 0.085), higher diversity gain (DG &gt; 9.95 dB), minimal channel capacity loss (&lt; 0.39 bits/s/Hz), and negligible magnitude variation in mean effective gain among the antenna ports (&lt; 0.1 dB). The acquired total active reflection (TARC) curve exhibits the antenna's robust resonance features over the application band and commendable time domain properties in the active spectral region. The findings of the simulation and measurements revealed a close alignment.

Ultra‐Broadband Visible‐DUV Supercontinuum Generation by Non‐Resonant Coherent Raman Scattering in Air

AbstractTo date, supercontinuum light in the visible and near‐infrared ranges is readily realizable by the optical Kerr effect through self‐phase modulation of ultrashort laser pulses in transparent media. However, it is still a challenge to extend the supercontinuum spectrum down to the deep‐ultraviolet (DUV) range, which is particularly needed for exploring ultrafast dynamics in chemistry, materials, and biology. Here, an approach of non‐resonant coherent Raman scattering is developed to generate ultra‐broadband visible‐DUV supercontinuum in ambient air with a spectral range spanning over 250 nm and a wavelength down to 220 nm. A rovibrational coherence is established in air molecules by filamentation of a near‐infrared femtosecond 800 nm pulse and two femtosecond Raman laser pulses at 267 and 400 nm are introduced into the coherent media to induce non‐resonant coherent Stokes and anti‐Stokes Raman scatterings, which serve as the spectral bridges to link the neighboring Raman pump laser spectra, resulting in ultra‐broadband supercontinuum light. The mechanism is further verified by examining the broadening of picosecond N2+ laser lines with narrow bandwidths (10–30 cm−1), which forms a supercontinuum spectrum spanning over 150 nm. The work provides a viable route for the establishment of coherent DUV supercontinuum in the gas media at designed wavelength ranges.

High-Performance Vis–NIR Photodetectors Based on Two-Dimensional Bi2Te3 Thin Film and Applications

Two-dimensional materials have excellent optoelectronic properties and have great significance in the field of photodetectors. We have prepared a thin film photodetector based on bismuth telluride (Bi2Te3) topological insulator using dual-temperature-zone vapor deposition technology. Due to the high-quality lattice structure of Bi2Te3 and the uniform and dense surface morphology of the Bi2Te3 thin film, the device exhibits excellent photoelectric response and Vis–NIR spectral range. Under 405 nm illumination, the responsivity is 5.6 mA/W, the specific detectivity is 1.22 × 107 Jones, and the response time is 262/328 ms. We designed a photodetector single-point scanning imaging system and successfully achieved high-resolution imaging at a wavelength of 532 nm. This work provides guidance for the application of two-dimensional materials, especially Bi2Te3, in the fields of photodetectors and imaging.