Search Results (49)

Amplified Spontaneous Emission (ASE) sources are widely employed as highly stable broadband sources in fields such as high-precision navigation and optical detection. Erbium-doped fiber (EDF), as the core active component in ASE sources, has long been a key subject of thermal stability research. We fabricated a low-doped EDF with an 80 μm-cladding using the vapor phase doping (VPD) technique. This EDF was compared with a commercial 125 μm-cladding EDF using a double-pass forward (DPF) optical path configuration with a narrowband filter. We investigated the temperature-dependent characteristics of the ASE spectra generated by the two EDFs with different parameters. The temperature drift performance of the two EDFs was analyzed based on three critical indicators of the spectrum: mean wavelength, spectral bandwidth, and output power. In comparison with the commonly used EDF, the results show that a properly designed small-cladding EDF with an appropriate length can deliver higher ASE output power and exhibit a lower mean-wavelength temperature drift. This study provides an important guideline for promoting the miniaturization of high-precision fiber-optic sensing devices. Full article

Background: Radiotherapy is essential for skull base tumor management but carries the risk of radiation-induced brain injury (RIBI). This spectrum ranges from transient radiation-induced contrast enhancement (RICE) to irreversible necrosis. Distinguishing these entities from tumor progression is critical, particularly with the increasing adoption of proton therapy. Methods: A comprehensive narrative review of the peer-reviewed literature was conducted up to October 1, 2025. The search strategy focused on adult patients treated for skull base malignancies, synthesizing data on dose–volume metrics, incidence rates, and modality-specific toxicity profiles. Results: RIBI represents a pathophysiological continuum. (a) Descriptive imaging patterns: In prospective proton therapy series, focal RICE occured in 15% of patients, typically at a median of 12 months, and often resolved spontaneously. (b) Modality comparison: Although proton therapy reduces integral brain dose versus photon therapy, elevated linear energy transfer (LET) at the distal Bragg peak may contribute to focal radiation-associated image changes (RAIC), particularly in the temporal lobes. (c) Risk stratification and diagnosis: Risk increased when >1% of the healthy brain received >57.6 Gy (Relative Biological Energy (RBE)) or when V67Gy exceeded 0.17 cc. Advanced MRI and amino acid positron emission tomography (PET) improved differentiation between radiation effects and tumor recurrence. Conclusions: Post-radiation imaging changes are common and often benign. Distinguishing RICE from progression requires multimodal imaging and adherence to specific dose constraints. Management should prioritize surveillance for asymptomatic lesions. Full article

Light–matter interactions in optical microcavities attract much attention due to their potential for controlling properties of materials. Among the various types of optical microcavities, porous silicon microcavities (pSiMCs) are of special interest because of their relatively simple fabrication procedure, tunable porosity, and large specific surface area, which make them highly suitable for a wide range of optoelectronic and sensing applications. However, the fabrication of pSiMCs with precisely controlled parameters, which is crucial for effective light–matter coupling, remains challenging due to the multiple variables involved in the process. In addition, the parameter characterizing the capacity of pSiMCs for confining light inside the cavity (the quality factor, QF) rarely exceeds 100. Here, we present advanced methods and protocols for controlled fabrication of pSiMCs at room temperature, combining theoretical and numerical simulations and experimental validation of microcavity structural parameters for enhancing light–matter interactions. This systemic approach has been used to design and fabricate pSiMCs with an about twofold increased QF and correspondingly improved optical performance; the theoretical modeling shows that its further development is expected to increase the QF even more. In addition, we fabricated hybrid fluorescencent structures with the R6G dye embedded into the optimized pSiMCs. This provided a 5.8-fold narrowing of the R6G fluorescence spectrum caused by light–matter coupling, which indicated enhancement of the fluorescence signal at the eigenmode wavelength due to an increased rate of spontaneous emission in the cavity. The proposed methodology offers precise theoretical simulation of microcavities with the parameters required for specific practical applications, which facilitates optimization of microcavity design. The controllable optical properties of pSiMCs make them promising candidates for a wide range of applications where improved spectral resolution, and increased luminescence efficiency are required. This paves the way for further innovations in photonic systems and optoelectronic devices. Full article

A general relativistic model of an astrophysical hypermassive extremely magnetized ultra-compact self-bound quark–gluon plasma (QGP: ALICE/LHC) object that is supported against its ultimate gravitational implosion by the simultaneous action of the vacuum polarization driven by nonlinear electrodynamics (NLED: ATLAS/LHC: light-by-light scattering)—the vacuum “awakening”—and the asymptotic freedom, a key feature of quantum chromodynamics (QCD), is presented. These QCD stars can be the final figures of the equilibrium of collapsing stellar cores permeated by magnetic fields with strengths well beyond the Schwinger threshold due to being self-bound, and for which post-supernova fallback material pushes the nascent remnant beyond its stability, forcing it to collapse into a hybrid hypermassive neutron star (HHMNS). Hypercritical accretion can drive its innermost core to spontaneously break away color confinement, powering a first-order hadron-to-quark phase transition to a sea of ever-freer quarks and gluons. This core is hydro-stabilized by the steady, endlessly compression-admitting asymptotic freedom state, possibly via gluon-mediated enduring exchange of color charge among bound states, e.g., the odderon: a glueball state of three gluons, or either quark-pairing (color superconductivity) or tetraquark/pentaquark states (LHCb Coll.). This fast—at the QGP speed of sound—but incremental quark–gluon deconfinement unbinds the HHMNS’s baryons so catastrophically that transforms it, turning it inside-out, into a neat self-bound QGP star. A solution to the nonlinear Tolman–Oppenheimer–Volkoff (TOV) equation is obtained—that clarifies the nonlinear effects of both NLED and QCD on the compact object’s structure—which clearly indicates the occurrence of hypermassive QGP/QCD stars with a wide mass spectrum ($0\lesssim {\mathrm{M}}_{\mathrm{Star}}^{\mathrm{QGP}}\lesssim$ 7 M_⊙ and beyond), for star radii ($0\lesssim R_{\mathrm{Star}}^{\mathrm{QGP}}\lesssim 24$ km and beyond) with B-fields (${10}^{14}\le {\mathrm{B}}_{\mathrm{Star}}^{\mathrm{QGP}}\le {10}^{16}$ G and beyond). This unexpected feature is described by a novel mass vs. radius relation derived within this scenario. Hence, endowed with these physical and astrophysical characteristics, such QCD stars can definitively emulate what the true (theoretical) black holes are supposed to gravitationally do in most astrophysical settings. This color quark star could be found through a search for its eternal “yo-yo” state gravitational-wave emission, or via lensing phenomena like a gravitational rainbow (quantum mechanics and gravity interaction), as in this scenario, it is expected that the light deflection angle—directly influenced by the larger effective mass/radius (${\mathrm{M}}_{\mathrm{Star}}^{\mathrm{QGP}}\left(B\right)$, ${\mathrm{R}}_{\mathrm{Star}}^{\mathrm{QGP}}\left(B\right)$) and magnetic field of the deflecting object—increases as the incidence angle decreases, in view of the lower values of the impact parameter. The gigantic—but not infinite—surface gravitational redshift, due to NLED photon acceleration, makes the object appear dark. Full article

The main characteristic of a reflective semiconductor optical amplifier chip (RSOA) is that it does not generate optical resonance under electric pumping and maintains the operation state of spontaneous emission. In this paper, a Nb₂O₅/SiO₂/Nb₂O₅/SiO₂ (four-layer Nb₂O₅/SiO₂) film system is employed as the coating material for the output facet of the RSOA. The 3 dB spectral width of the spontaneous emission spectrum from this RSOA reaches 79.4 nm, with a ripple of less than 1 dB occurring across this wavelength range. Notably, around the 1550 nm wavelength, the ripple is as low as 0.5 dB. This represents the best performance reported for this type of chip. The RSOA is packaged as a narrow-linewidth external cavity laser. Under test conditions of 25 °C and 180 mA, the external cavity laser produces an output power of 12.6 mW and achieves a linewidth of 299.8 Hz. Furthermore, by adjusting the Fabry–Pérot (FP) standard cavity, filtering, and other external cavity parameters, the lasing spectrum of the narrow-linewidth external cavity laser based on the RSOA is tunable across a wavelength range from 1535.83 nm to 1561.42 nm, which shows the usability of the proposed ROSA for a C-band external cavity narrow-linewidth laser. Full article

Spices and aromatic herbs are important components of everyday nutrition in several countries and cultures, thanks to their capability to enhance the flavor of many dishes and convey significant emotional contributions by themselves. Indeed, spices as well as aromatic herbs are to be considered not only for their important values of antimicrobial agents or flavor enhancers everybody knows, but also, thanks to their olfactory and gustatory spectrum, as drivers to stimulate the consumers’ memories and, in a stronger way, emotions. Considering these unique characteristics, spices and aromatic herbs have caught the attention of consumer scientists and experts in sensory analysis for their evaluation using semi-quantitative approaches, with interesting evidence. In this pilot study as a first step, each studied botanical, belonging to Piperaceae or aromatic herbs, has been subjected to headspace solid phase micro-extraction (HS-SPME) coupled with gas-chromatography mass spectrometry (GC-MS) analysis to assess their spontaneous volatile emission, representing the complex chemical pattern, which encounters the consumers’ olfactory perception. Furthermore, the present investigation, performed on 12 individuals, outlines the administration of a pilot study, merging the typical sensory analysis with emotional data collection and the innovative contribution related to the study around the Autonomic and Central Nervous System activation in consumers, performed using wearable technologies and related signal processing. The results obtained by our study, beyond demonstrating the feasibility of the approach, confirmed, both in terms of emotional responses and biomedical signals, the significant emotional potential of spices and aromatic herbs, most of which featuring an overall positive valence, yet with inter-subjects’ variations. Future investigations should aim to increase the number of volunteers evaluated with such an approach to draw more stable conclusions and attempting a customization of product preferences based on both implicit and explicit sensory responses. Full article

Organic solid-state lasers are highly promising devices known for their low-cost fabrication processes and compact sizes and the tunability of their emission spectrum. These lasers are in high demand across various industries including biomedicine, sensors, communications, spectroscopy, and military applications. A key requirement for light-emitting materials used in a light-amplifying medium is a low threshold value of the excitation energy of the amplified spontaneous emission (ASE). A newly synthesized non-symmetric red-light-emitting laser dye, Ethyl 2-(2-(4-(bis(2-(trityloxy)ethyl)amino)styryl)-6-tert butyl-4H-pyran-4-ylidene)-2-cyanoacetate (KTB), has shown great promise in meeting this requirement. KTB, with its attached bulky trityloxyethyl groups, has the ability to form amorphous thin films from a solution using a wet-casting method. Recent experiments have demonstrated that KTB exhibits a low ASE threshold value. This study focused on investigating the optical and amplified spontaneous emission properties of KTB in poly(N-vinylcarbazole) (PVK), polysulfone (PSU), and polystyrene (PS) matrices at various concentrations. The results showed that as the concentration of the dye increased, a redshift of the photoluminescence and ASE spectra occurred due to the solid-state solvation effect. The lowest ASE threshold value of 9 µJ/cm² was achieved with a 20 wt% concentration of KTB in a PVK matrix, making it one of the lowest excitation threshold energies reported to date. Full article

In order to address the ‘capacity crisis’ caused by the narrow bandwidth of the current C band and the demand for wide-spectrum sensing sources and tunable fiber lasers, a broadband luminescence covering the C + L bands using Er³⁺/Yb³⁺ co-doped fluorotellurite glass fiber is investigated in this paper. The optimal doping concentrations in the glass host were determined based on the intensity, lifetime, and full width at half maximum (FWHM) of the fluorescence centered at 1.5 µm, which were found to be 1.5 mol% Er₂O₃ and 3 mol% Yb₂O₃. We also systematically investigated this in terms of optical absorption spectra, absorption and emission cross-sections, gain coefficients, Judd–Ofelt parameters, and up-conversion fluorescence. The energy transfer (ET) mechanism between the high concentrations of Er³⁺ and Yb³⁺ was summarized. In addition, a step-indexed fiber was prepared based on these fluorotellurite glasses, and a wide bandwidth of ~112.5 nm (covering the C + L bands from 1505.1 to 1617.6 nm) at 3 dB for the amplified spontaneous emission (ASE) spectra has been observed at a fiber length of 0.57 m, which is the widest bandwidth among all the reports based on tellurite glass. Therefore, this kind of Er³⁺/Yb³⁺ co-doped fluorotellurite glass fiber has great potential for developing broadband C + L band amplifiers, ultra-wide fiber sources for sensing, and tunable fiber lasers. Full article

The existence of amplified spontaneous emission (ASE) is a fundamental principle of laser dyes. ASE indicates the spectral variation of the optical gain of a laser dye. Analyzing the spectral distribution of ASE is important for designing lasers. We demonstrate ASE investigations on planar waveguides made of a (co-)polymer. Similar to organic DFB (distributed feedback) lasers, a line grating allows a partial decoupling of the guided radiation. This decoupled radiation is detected as an indicator of the guided radiation. The diffraction of the radiation is utilized to perform a spectrally selective investigation of the ASE by spatially splitting it. This analysis method reduces the influence of isotropic photoluminescence and allows ASE to be analyzed across its entire spectrum. We were able to observe ASE in F8BT over a range from ${\lambda }_{ASE,min}$ = 530 nm to ${\lambda }_{ASE,max}$ = 570 nm and determine ASE threshold power densities lower than $E_{ASE}<$ 2.57 μJ/cm². The study of the power density of the ASE threshold is performed spectrally selectively. Full article

An easy-to-implement and cost-effective Fiber Bragg Grating (FBG) sensor interrogation technique based on a ring Erbium-Doped Fiber Laser (EDFL) topology is proposed and experimentally assessed. The FBG sensor is part of the EDFL cavity and must have a central wavelength located within the linear region of the EDF’s amplified spontaneous emission (ASE) spectrum, which occurs at between 1530 and 1540 nm. In this manner, the wavelength-encoded response of the FBG under strain is converted to a linear variation in the laser output power, removing the need for spectrum analysis as well as any limitations from the use of external edge-filtering components. In addition, the laser linewidth is significantly reduced with respect to the FBG bandwidth, thus improving the resolution of the system, whereas its sensitivity can be controlled through pumping power. The performance of the system has been characterized by modeling and experiments for EDFs with different lengths, doping concentrations, and pumping power levels. The influence of mode-hopping in the laser cavity on the resolution and accuracy of the system has also been investigated. Full article

In this study, we investigate the time–frequency-resolved resonant photon emission from a molecular vibrational oscillator driven by a monochromatic coherent external field. Using the complex spectral analysis of the Liouvillian, which integrates irreversible dissipative phenomena into quantum theory, we elucidate the fundamental processes of photon emission. Indeed, our analytical approach successfully decomposes the emission spectrum into two intrinsic contributions: one from a resonance eigenmode and another from continuous eigenmodes. These components are responsible for incoherent luminescence and coherent scattering photon emission processes, respectively. Our results show that while spontaneous emission dominates in the early stages of the emission process, coherent scattering gradually becomes more pronounced with time. Furthermore, destructive quantum interference between the two components plays a key role in determining the overall shape of the emission spectrum. Full article

The interaction of nanostructured metal particles with the molecular components of biosystems differs significantly from the processes that take place in the presence of ions of the same metals. This unequivocally indicates the need to take into account not only the course of chemical processes but also implies to discuss certain physical effects that are usually neglected when considering such interactions. In this work, we studied the interaction of silver nanoparticle dispersion (Ag-NP) in ethylene glycol with a particle size less than 100 nm (Sigma-Aldrich 658804) with glutathione in a water and carbonate buffer (pH 10). The choice of glutathione (GSH) is due to the fact that it plays a significant role in intracellular processes, participating in the protection of intracellular components from the toxic effects of heavy metal ions; at the same time, differences in its interaction with silver ions and nanoparticles were experimentally demonstrated. A series of optical studies of the absorption and emission spectra of solutions of silver nanoparticles with GSH was carried out in order to establish the dominant processes in the system. It was shown that the above-mentioned silver nanoparticles in aqueous solutions spontaneously decompose over time, while glutathione differently affects these processes in water and carbonate buffer. It was shown that not only the local surface plasmon resonance bands but also the emission spectra of Ag-NP~GSH solutions in the region of 350–550 nm change with time. The sources of such radiation can be carbon quantum dots (CQD), which, according to published data, can be formed during the synthesis of silver nanoparticles and effectively luminesce in this region of the spectrum. Raman spectroscopy data confirm the presence of CQD in the Ag-NPs solution. The presence of quantum dots in the system makes it possible to indirectly track the presence of silver nanoparticles, which are booster centers, enhancing the emission of CQDs. The studies allow us to state that the interaction of glutathione with silver nanoparticles is a complex topochemical process in which, in addition to chemical reactions, the processes of transformation of silver nanoparticles and changes in the distribution of their sizes and chemical/physical functionality take place. Full article

We examine theoretically the effect of bismuth chalcogenide microparticles on the spontaneous emission of a double-V-type quantum emitter in free space. We have found, in particular, that the presence of a single microparticle causes a high degree of quantum interference in the way the quantum emitter releases energy in the process of spontaneous emission. This, in turn, leads to significant changes in the spectrum of the emitted energy. The quantum emitter’s initial state is crucial to how the energy is released in the presence of the microparticle. This observation has potential implications for quantum computing, particularly for reading the state of atomic qubits. When two microparticles are present, the effect is more pronounced, particularly when the quantum emitter is located in the gap between the particles. Full article

This paper presents a real-time remote water level monitoring system based on dense wavelength division multiplexing (DWDM)-passive optical fiber sensor (OFS) network for the application of the Internet of Things (IoT). This network employs a broadband light source based on amplified spontaneous emission (ASE) as a seed light. This ASE light is spectrum-sliced by an athermal type arrayed waveguide grating (200 GHz × 16 channel), then distributed towards multiple sensing units (SU). Here, 16 SUs are installed vertically at the specified height in the water pool according to the design specification (i.e., spatial resolution). Then, each SU reflects an optical spectrum having a different reflection coefficient depending on the surrounding medium (e.g., air or water). By measuring these reflected optical spectra with an optical spectrum analyzer, the water level can be easily recognized in real time. However, as the sensing distance increases, system performance is severely degraded due to the Rayleigh Back-Scattering of the ASE light. As a result, the remote sensing capability is limited at a short distance (i.e., <10 km). To overcome this limitation, we propose a simple signal processing technique based on feature extraction of received optical spectra, which includes embedding a peak detection algorithm with a signal validation check. For the specific, the proposed signal processing performs the peak power detection, signal quality monitoring, and determination/display of the actual water level through three function modules, i.e., data save/load module, signal processing module, and Human–Machine Interface display module. In particular, the signal quality of the remote sensing network can be easily monitored through several factors, such as the number of spectral peaks, the wavelength spacing between neighboring peaks and the pattern of detected peak power. Moreover, by using this validation check algorithm, it is also possible to diagnose various error types (such as peak detection error, loss of data and so on) according to the pattern of measured optical spectra. As a result, the IoT sensor network can recognize 17 different level statuses for the water level measurement from a distance of about 25 km away without active devices such as optical amplifiers (i.e., passive remote sensing). Full article

The introduction of biuret hydrogen-bonding sites onto chiral binaphthalene-based chromophores was investigated as a route to sub-micron-sized, vesicle-like aggregates endowed with chiroptical properties. The synthesis was conducted from the corresponding chiral 4,4′-dibromo-1,1′-bis(2-naphthol) via Suzuki–Miyaura coupling to afford luminescent chromophores whose emission spectrum could be tuned from blue to yellow-green through extension of the conjugation. For all compounds, the spontaneous formation of hollow spheres with a diameter of ca. 200–800 nm was evidenced by scanning electron microscopy, along with strong asymmetry in the circularly polarized absorption spectra. For some compounds, the emission also displayed circular polarization with values of g_lum = ca. 10^–3 which could be increased upon aggregation. Full article