Search Results (368)

Today, the rapid progress in non-invasive light–matter interaction analysis is transforming the landscape of biomedical and life sciences driven by low-intensity light detection technologies. As the complexity of photonic applications continues to grow, the importance of single-photon detection techniques becomes pivotal. Among them, Time-Correlated Single-Photon Counting (TCSPC) has become the gold standard for precise, time-resolved reconstruction of rapid and faint optical signals. However, TCSPC has long been constrained by pile-up distortion, which worsens with increasing acquisition speed, typically limiting it to 5% of the excitation frequency. To overcome the operational constraints of conventional implementations, a novel TCSPC acquisition methodology has been introduced, independent of photodetector dead time, excitation intensity, and prior optical signal knowledge, still enabling distortion-free reconstruction of the measured light profiles. In this context, the development of single-photon detectors with short dead time and low timing jitter becomes crucial. This work presents a single-photon detection module based on a Silicon Photomultiplier, which delivers 750 ps FWHM output pulses with a 33.5 ps RMS IRF. Its performance is showcased through fluorescence measurements employing the constraint-free TCSPC methodology, achieving a photon count rate up to 166% of the excitation frequency with a minimal lifetime estimation error of just −1.46%. Full article

Dry eye disease (DED) is a chronic inflammatory disorder of the ocular surface, characterized by tear film homeostasis imbalance, with aging being identified as a crucial independent risk factor. Oxidative stress, which refers to the excessive production of reactive oxygen species (ROS) and reactive nitrogen substances during mitochondrial metabolism and the weakened protective effect of antioxidants, plays a central role in this process. With aging, the mitochondrial function of ocular surface tissues, such as the corneal epithelium, meibomian glands, and lacrimal glands, declines. Concurrently, the activity of endogenous antioxidant enzymes (such as superoxide dismutase and glutathione peroxidase) decreases, and the levels of tear antioxidants such as lactoferrin also decrease. These age-related changes collectively lead to excessive accumulation of ROS, triggering oxidative stress that directly damages biomacromolecules in ocular surface cells and impairs the stability of the tear film. Furthermore, we have summarized the current therapeutic strategies for oxidative stress in DED, including both conventional antioxidants and emerging approaches such as eye drops based on nanoenzymes, thermosensitive hydrogels, intense pulsed light therapy, and drug-eluting contact lenses. By combining the new progress in the delivery systems of biomaterials-based drugs with mechanism-guided interventions, this review systematically establishes the intimate functional linkages between mitochondrial dysfunction, oxidative stress, and the pathogenesis of DED and focuses on elaborating the translational potential of advanced biomaterials-based antioxidant regimens, aiming to provide novel foundations and insights theoretical for the development of more effective and precise therapeutic strategies for DED. Full article

Light-based therapies are becoming increasingly = more mainstream, not only within the medical science space, but also within the fields of cosmetic dermatology and personal grooming. Intense Pulsed Light (IPL) harnesses the ability of the natural chromophore–melanin to absorb light energy, which is translated into heat energy and consequently results in targeted thermolysis of cells rich in melanin. This mechanistic pathway lends itself to a wide range of applications, including long-term hair removal, skin rejuvenation, the treatment of unwanted pigmentation, and the treatment of ophthalmic conditions. The development of home use devices (HUDs) for the delivery of IPL-mediated hair removal has facilitated the self-administration of photothermal treatments and reduced reliance on clinical settings. In this study, we demonstrate a pioneering approach to model aspects of IPL-induced thermal induction and selective thermolysis in a complex human skin tissue equivalent. Our approach utilised a deactivated HUD with disabled safety features that allowed for the exposure of tissue constructs to high-fluence IPL. We demonstrate an increase in biomarkers consistent with increased cellular temperature, induction of apoptosis, and increased pro-inflammatory cytokine release following extreme treatment regimens, all of which correlate with an increased fluence and/or increased number of IPL pulses delivered. This method allowed for the identification of cellular events evoked by increasing fluence and extreme-exposure regimes. Full article

Radiation of X-ray pulsars is powered by accretion on the neutron star surface from a binary companion under the influence of a strong magnetic field. We study the beaming of this radiation in the case of subcritical X-ray pulsars, where it is formed in the accretion channel close to the neutron star surface. We solve equations of the hydrodynamics and radiative transfer of two coupled polarization modes in the accretion channel numerically, taking into account resonant Compton scattering and vacuum polarization. The beaming patterns are obtained for different accretion rates, photon energies, and polarizations, as well as for different models of the neutron star surface radiation. The calculated beaming patterns are converted into light curves for both the intensity and polarization, taking into account the effects of General Relativity. These beaming patterns and light curves are found to be strongly affected by the resonant Compton scattering for photon energies comparable with the electron cyclotron energy. In particular, the angular redistribution of radiation near the cyclotron resonance may reduce the light-curve modulation amplitude, which is consistent with observational indications of a suppressed pulsed fraction at these energies. Full article

Polarity-tunable photocurrents provide an intrinsic decision variable that enables in-sensor computing within a single device, moving beyond simple intensity detection toward next-generation intelligent vision, yet traditional photodetectors are limited by static doping profiles and fixed junction polarities. To overcome this bottleneck, we propose a Te_0.61Se_0.39 nanowire device with polarity-tunable photoresponse for broadband optoelectronic logic operation via photocarrier diffusion under localized light illumination. By simultaneously harnessing temporal (pulse width), spatial (light positions), amplitude (light intensity), and bias, our polarity-tunable devices deterministically realize the four fundamental Boolean logic gates (AND, NAND, XNOR, XOR), with a responsivity of 1.39 A/W and a specific detectivity of 1.75 × 10¹⁰ Jones across the visible to mid-wave infrared spectrum. We further showcased its scalability by constructing a two-layer composite Boolean circuit through the integration of optoelectronic AND and NAND gates. Practical applications in optical encoding/decoding transmission and differential perception highlight its broad functional adaptability. This work establishes a paradigm for broadband polarity devices in low-dimensional nanowires, providing a versatile platform for optoelectronic logic and differential imaging applications. Full article

Artificial lighting is a central and resource-intensive component of controlled environment agriculture, directly regulating plant physiological processes while influencing energy efficiency and production outcomes. Chlorophyll fluorescence analysis, particularly pulse-amplitude-modulated fluorometry, provides a rapid and non-destructive method for assessing plants’ photosynthetic efficiency. However, the extent to which chlorophyll fluorescence reflects plant responses to different light spectra across species remains insufficiently understood. In this study, species-specific photoresponses of leafy vegetables (Amaranthus tricolor, Barbarea verna, Chrysanthemum coronarium, Perilla frutescens) to different light spectra were investigated by integrating chlorophyll fluorescence with growth, antioxidant, and pigment traits. Plants were cultivated under monochromatic red, blue, and combined red–blue light, with additional far-red supplementation. Correlation analysis was performed among growth, antioxidant parameters, pigment contents, and chlorophyll fluorescence parameters. The obtained results show that chlorophyll fluorescence parameters respond selectively, but species-specifically, to applied lighting-spectrum conditions. Relationships between fluorescence indices and physiological traits varied between species, and no single parameter consistently reflected plant performance across all crops. Therefore, to employ chlorophyll fluorescence as a useful proxy for assessing plant responses to lighting spectrum, a species-specific and context-dependent approach is required. Full article

Understanding the effects of light on the body at different times of the 24 h solar day is a topic of increasing interest. In this paper, we use a mathematical model from the literature to simulate what would be expected of the human circadian clock on different light schedules. We first reproduce an influential experiment which found eBooks, when compared to a paper book, delayed sleep by roughly 10 min and melatonin onset by 1.5 h. The model is able to match the delay in sleep onset but struggles to reproduce the melatonin phase delay. However, certain initial conditions and parameters are capable of phase shifts consistent with the original study’s magnitude, suggesting that the original study’s finding may have been influenced by the pre-study entrainment or variability among the participants. We next simulate the same protocol under higher daytime light levels (increasing baseline illumination from 90 to 500 lux) and find that brighter daytime exposure reduces both sleep onset latency and the variability in phase delay attributable to evening eBook light. Finally, we explore how the timing of a bright light pulse during the day changes outcomes, such as sleep onset and circadian amplitude, and how these effects interact with light during the other hours of the 24 h day. Together, these modeling results suggest robust daytime light exposure confers resilience against the circadian-disruptive effects of evening light, generating testable predictions regarding the timing and intensity of beneficial light interventions for maintaining circadian alignment. Full article

Background: Melasma is a chronic hypermelanosis requiring effective therapies. Methods: This prospective, randomized controlled trial evaluated intense pulsed light (IPL) and topical tranexamic acid (TXA) versus IPL with placebo. Thirty-three patients completed the 5-month study (group A: TXA + IPL, n = 17; group B: Placebo + IPL, n = 16). Outcome included VISIA analysis, modified Melasma Area and Severity Index (mMASI), skin melanin index (MI) and erythema index (EI) measurement. Results: At Month 5, both groups showed improved mMASI scores; however, group A demonstrated a significantly greater reduction than group B (−50.52% vs. −38.49%; mean difference −12.03%, 95% CI −23.74% to −0.32%; p < 0.05). Excellent improvement was achieved in 70.59% of Group A versus 25% of Group B. Furthermore, Group A exhibited a significant decrease in MI (−36.31%) compared to a negligible change in Group B (−1.28%), with a significant between-group difference (p = 0.02). VISIA analysis confirmed superior improvements in brown spots and texture for Group A (p < 0.05). No adverse events occurred. Conclusions: Combining topical TXA with IPL is a safe and significantly more effective treatment for melasma than IPL alone, offering superior pigment reduction without increased risks. Full article

Optical klystrons have been developed in storage ring free-electron lasers (FELs) as insertion devices to increase the FEL gain in a straight section with limited length. By adjusting the magnetic field in the dispersion section of the optical klystron to shift the relative delay between the electron bunch and FEL pulse from an integer multiple of the FEL wavelength, FELs can oscillate at two wavelengths. The electron density of the electron bunch that interacts with the FEL pulse in a small-signal regime is modulated at the FEL wavelength period. When the FEL oscillates simultaneously at two wavelengths, the electron density of the electron bunch beats through the modulation with two periods. This beat generates long-wavelength coherent edge radiation at a bending magnet located in the straight section containing the optical klystron. Difference-frequency waves induced by dual-wavelength ultraviolet free-electron lasers generate a high-intensity mid-infrared monochromatic beam. Our findings will lay the foundation for the development of the difference-frequency waves of soft X-rays and extreme ultraviolet light using hard X-ray FELs. Full article

This study investigated the impact of the pretreatment of pea plants (Pisum sativum L. Ran 1) for five days by three times higher light intensity (360 μmol m⁻² s⁻¹) than the intensity for their cultivation (120 μmol m⁻² s⁻¹) on the photosynthetic apparatus’s ability to withstand moderately high temperatures. Photosystem II (PSII) performance was assessed by pulse amplitude-modulated (PAM) fluorometry—evaluation of F_v/F_m, Chl fluorescence decrease ratio—R_Fd, excitation pressure on PSII (1 − qP), non-photochemical quenching (NPQ) analysis, and PsbA (D1) abundance. The redox state of P700 was used to examine photosystem I (PSI), and the redox kinetics of P700 was evaluated as an estimate of cyclic electron flow (CEF). The energy distribution and interaction between the two photosystems were assessed by 77 K chlorophyll fluorescence. Diphenylhexatriene (DPH) fluorescence polarization and PsbS accumulation were followed to estimate alterations in thylakoid membrane characteristics. Our data show that pea plants pretreated with a higher level of light intensity showed higher resistance to temperature increase, maintaining R_Fd values similar to control plants, and the effect of high temperature on PSII excitation pressure (1 − qP) was mitigated. A significant difference between the two groups of plants was observed in terms of quantum yields in both types of non-photochemical quenching, with light pretreated plants showing no change in the energy partitioning ratio while the exposure of non-high light pretreated plants to elevated temperatures led to a more significant increase in quantum yield of constitutive non-photochemical quenching. When plants were exposed to higher temperature, the accumulation of PsbS, induced by high light treatment, was accelerated, and stabilization of thylakoid membrane also occurred. A complex mechanism behind the enhanced tolerance to higher temperature includes the reorganization of membrane pigment–protein complexes, which is regulated by the buildup of PsbS and the accompanying redistribution of excitation energy. Full article

Rosacea is a chronic inflammatory skin disease characterized by erythematous, papular, and pustular lesions. Treatment for rosacea is tailored to the type and severity of lesions and the individual needs of the patient. The primary therapy involves topical and systemic treatments. Laser therapy is also an effective method. This review summarizes current knowledge on the application of pulsed dye lasers (PDLs), potassium titanyl phosphate (KTP) lasers, intense pulsed light (IPL), neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers, carbon dioxide (CO₂) lasers, and erbium-doped yttrium aluminum garnet (Er:YAG) lasers in the treatment of rosacea. Research confirms that the PDL remains the gold standard, demonstrating excellent clinical efficacy. The KTP and IPL lasers provide comparable outcomes, with relatively fewer adverse effects. Due to its greater depth of penetration, the Nd:YAG laser is used to treat lesions in the deeper layers of the skin. In advanced forms of rosacea, such as rhinophyma, ablative lasers, including CO₂ and Er:YAG, are employed. This review summarizes the mechanisms of action, therapeutic applications, and adverse effects associated with the use of various laser types in the management of rosacea. Full article

This paper investigates a novel optical method that uses a high-responsivity a-Si:H photodiode for label-free detection of luminescence from HeLa cervical cancer cells excited by a blue LED. We examine the energy distribution of the energy-gap density of states (DOS) from the photodiode’s long-time transient current, which shows exponential decay kinetics in the HeLa cell reaction. We analysed the transient response of a-Si:H p-i-n photodiode upon the illumination of the analyte with a pulsed blue LED light to better understand the HeLa cells activity and the fundamental defect kinetics processes in the a-Si:H material. Results suggest that the characteristic very low-level, time-varying light response of HeLa cells is due to chemiluminescence within cells, resulting from the reaction between nitric oxide (NO) and hydrogen peroxide (H₂O₂). Given the low signal intensity and noise, we applied a Savitzky–Golay (SG) filter to post-process the data. By reducing noise without attenuating chemiluminescent peaks, the Savitzky–Golay filter enabled accurate, reproducible quantification of the photocurrent response, reflecting the kinetics of cellular reactions. Further studies and more precise measurement instruments are needed for this real-time, label-free, non-destructive method, which applies SG-filtered signal processing to microfluidic optical biosensors. Full article

All-optical memristors possess light-sensing and storage capabilities while simultaneously simulating human synaptic functions, demonstrating immense potential in the field of brain-inspired computing for realizing bionic synapses and brain-like intelligence. In this work, we successfully produced ε-Ga₂O₃ films, ε/β-Ga₂O₃ mixed-phase films, and β-Ga₂O₃ films via chemical vapor deposition (CVD). The optical output and optical response characteristics of the thin films are investigated under 254 nm and 365 nm lasers. The CVD-grown ε-Ga₂O₃ is found to process a small amount of defects and insignificant memristive properties and the β-Ga₂O₃ obtained from the annealing of ε-Ga₂O₃ exhibits superior crystal quality but lacks memristive properties, while the ε/β-Ga₂O₃ mixed-phase films grown directly by CVD contain a fair amount of defects and demonstrate persistent resistance retention exceeding 104 s. Based on the excellent memristive properties of ε/β-Ga₂O₃ mixed-phase films, we conducted experiments simulating optical synapses. By adjusting optical pulse parameters (intensity, repetition rate, and duration), we successfully modeled the short-term plasticity (STP) and long-term plasticity (LTP) observed in biological synapses. Experiments confirm that light stimulation can effectively induce synaptic behaviors, such as the progressive conversion of short-term memory (STM) into long-term memory (LTM), and further fully reproduce the neuroplasticity process of “learning-forgetting-relearning.” This study demonstrates a photoconductive synapse memristor based on the wide-bandgap material gallium oxide, exhibiting exceptional air stability with sustained photoconductivity maintained for over a year. This study provides new insights into the practical application feasibility of all-optical artificial synapses based on gallium oxide. Full article

Background/Objectives: Septic shock involves severe circulatory and microcirculatory dysfunction and often requires vasopressors to maintain adequate mean arterial pressure (MAP). Conventional monitoring mainly reflects macrocirculation and may not capture changes in vascular tone or microcirculation. Remote photoplethysmography (rPPG) is a contactless optical method that analyzes peripheral pulse waveforms and may offer additional physiological insight during vasopressor therapy. The aim of this study was to assess the feasibility of rPPG for detecting pulse waveform changes associated with norepinephrine administration in septic shock. Methods: Prospective case series included three adult patients (n = 3) with septic shock admitted to the intensive care unit at Pauls Stradins Clinical University Hospital, Riga, Latvia. All patients received standard sepsis treatment, including fluid resuscitation and titrated norepinephrine to maintain MAP ≥ 65 mmHg. Continuous invasive arterial pressure monitoring was performed alongside rPPG signal acquisition from the palmar skin surface under controlled lighting. From averaged rPPG waveforms, perfusion index (PI), dicrotic notch amplitude (c-wave), and diastolic wave amplitude (d-wave) were extracted. Correlations between norepinephrine dose, MAP, and rPPG parameters were explored. Results: Increasing norepinephrine doses were associated with higher MAP and PI in all patients. Dicrotic notch and diastolic wave amplitude decreased consistently. These changes occurred alongside macrocirculatory stabilization and are consistent with increased vascular tone and altered arterial compliance. Conclusions: rPPG demonstrated feasibility for detecting pulse waveform changes during norepinephrine therapy in septic shock; however, larger controlled studies are required for validation. Full article

Newborns are unable to reliably express changes in their physical condition due to their physiological immaturity and limited capacity for communication; therefore, continuous and systematic monitoring during phototherapy is essential to ensure timely detection of adverse responses and maintenance of therapeutic safety. This study extends our prior work, which introduced an indirect method for measuring light intensity to improve precision in monitoring newborn skin illumination. Light-emitting diode (LED) phototherapy has attracted considerable attention as an effective treatment for neonatal jaundice (NNJ). This study introduces an three-dimensional configuration of blue LEDs. An Arduino Mega 2560 microcontroller with pulse-width modulation (PWM) technology was employed to independently regulate the intensity of LED strips, enabling precise control of light output. The strips were mounted on an arc-shaped structure that can be adjusted mechanically and electronically through pre-programmed instructions embedded in the microcontroller. The results demonstrate that blue light at a wavelength of 460 ± 10 nm aligns with the peak absorption spectrum of bilirubin, thereby optimizing the efficacy of phototherapy for NNJ. Both observed absorption peaks were within the therapeutically effective range. Computer simulations confirmed that stable output contours can be achieved using rapid electronic scanning with a PID control algorithm to dynamically adjust the duty cycle. Experimental data showed that LED radiation output was largely linear. This supports the use of linear control algorithms and confirms the platform’s feasibility for future research. Full article