Search Results (282)

The photoreceptor bacteriorhodopsin (HsBR) from Halobacterium salinarum is a model system for studying ultrafast photoinduced reactions in proteins. Recent time-resolved serial femtosecond crystallography (TR-SFX) experiments require high pump energies, raising concerns about nonlinear excitation and multi-photon effects. Here, we systematically investigate the influence of excitation energy, pulse duration and the sign of the chirp on the initial HsBR photo-reaction using femtosecond Vis-pump IR-probe spectroscopy in the retinal C=C stretching region. An acousto-optic programmable dispersive filter enabled independent control of pulse energy and chirp. Within the tested range, the retinal dynamics were independent of pulse duration and chirp, indicating that fluence alone does not fully describe excitation conditions. Increasing excitation energy leads to nonlinear saturation of the retinal signals and the appearance of an additional band near 1550 ${\mathrm{cm}}^{-1}$. However, this band rises linearly with the excitation energy. Hence, the additional band is not directly caused by non-resonant multi-photon absorption. Spectral decomposition reveals two components: a low-energy contribution consistent with the known retinal isomerization dynamics and a high-energy contribution attributed to a small population of photo-damaged HsBR likely formed via a resonant two-photon process. These findings clarify the role of excitation conditions in ultrafast HsBR spectroscopy and suggest that spectral changes at high pump energies mainly arise from damaged species upon resonant two-photon excitation. Full article

Terahertz radiation exhibits significant potential for communications, imaging, and spectroscopy. However, the development of efficient and low-cost THz detectors remains challenging due to limitations such as insufficient sensitivity, slow response speed, and poor room temperature stability. This work presents an innovative quasi-2D perovskite/Weyl semimetal (Co₃Sn₂S₂) heterojunction THz detector that combines complementary material properties via band engineering. The device achieves a remarkable responsivity of 374.15 A/W, a specific detectivity of 6.27 × 10¹¹ cm·Hz^1/2·W⁻¹, and a noise-equivalent power of 0.29 pW·Hz^−1/2 at 0.1 THz. This performance stems from the strong THz absorption of the perovskite layer combined with the high carrier mobility and topological surface states of the Co₃Sn₂S₂, which collectively enable ultrafast carrier extraction and suppressed interfacial recombination. This heterojunction design offers a novel strategy for high-performance terahertz detection and facilitates its integration into next-generation portable, integrated devices. Full article

Ultrafast fiber lasers operating near 2 μm have emerged as a critical platform for advancing mid-infrared photonics due to their narrow pulse durations, high peak powers, and broad tunability. These sources exploit the rich energy-level structures of Tm³⁺ and Ho³⁺ doped fibers and reside within an atmospheric transmission window, enabling applications spanning nonlinear microscopy, precision micromachining, optical frequency metrology, biophotonics, and free-space optical communication. Recent progress in low-loss fiber fabrication, dispersion-engineered cavity design, and mode-locking technologies has significantly expanded the performance boundaries of 2 μm ultrafast fiber lasers. This review systematically examines the underlying pulse-formation mechanisms and categorizes state-of-the-art mode-locking approaches. Representative laser architectures are compared with respect to pulse duration, energy scalability, repetition-rate enhancement, spectral characteristics, and environmental stability. Key application pathways in high-resolution spectroscopy, biomedical diagnostics, and mid-IR supercontinuum generation are highlighted. Finally, the remaining challenges and prospective research directions are discussed to inform the development of next-generation ultrafast photonic sources in the 2 μm band. Full article

Topological insulators (TIs) feature unique Dirac fermion-hosting surface states with exceptional electronic properties, rendering them promising candidates for optoelectronic and spintronic applications. Herein, we investigate the relaxation dynamics of photoexcited carriers in Bi₂Se₃ films via optical pump–terahertz (THz) probe spectroscopy (OPTP) at room temperature. Under 800 nm pump pulse excitation, the time-dependent real part of the pump excitation conductivity Δσ exhibits a positive-to-negative sign reversal as carriers relax toward equilibrium, which is further validated by frequency-dependent conductivity spectra at varied pump-probe delays. The initial positive Δσ originates dominantly from bulk carrier contributions, while the negative component at prolonged delays is ascribed to Dirac surface states, driven by enhanced scattering of photoexcited carriers. Using the Drude–Smith model to fit the differential conductivity spectra, we quantitatively extracted time-dependent transport parameters of bulk and surface states. These results unravel the comprehensive carrier relaxation mechanism in Bi₂Se₃, clarify the distinct roles of surface and bulk contributions, and lay the groundwork for designing TI-based THz devices. Full article

We report on sub-50 fs pulse generation from a diode-pumped mode-locked laser based on an ytterbium-doped monoclinic potassium yttrium double tungstate crystal operating in the 1 μm spectral region. Pumping by a low-power, spatially single-mode, fiber-coupled laser diode at 976 nm, a maximum continuous-wave output power of 433 mW at 1066.1 nm was obtained. Using a quartz-based intracavity Lyot filter, an exceptionally broad continuous-wavelength tuning range of 98 nm was achieved. In the mode-locked regime, the diode-pumped Yb:KY(WO₄)₂ laser delivered soliton pulses as short as 46 fs at a central wavelength of 1069.2 nm by employing a SEmiconductor Saturable Absorber Mirror. To the best of our knowledge, these results represent the broadest continuous-wave tuning range and the shortest pulse duration ever reported for lasers based on ytterbium-doped monoclinic double tungstate crystals. Full article

Ultrafast spin dynamics is a core research focus for advancing ultrafast spintronic devices, yet its accurate quantitative probing remains a challenge with conventional time-resolved techniques. Herein, we employ double-pump optical pump–terahertz emission spectroscopy (OPTE) to investigate the ultrafast spin dynamics of a Pt/Gd₁₉(Co_0.8Fe_0.2)₈₁/Ta ferrimagnetic rare-earth–transition-metal heterostructure. Experimental measurements resolve a single-step ultrafast demagnetization process with a characteristic time of ~0.42 ± 0.02 ps, followed by two-stage magnetic recovery involving a fast relaxation and a slow relaxation process. The fast and slow recovery time constants show a distinct positive dependence on the control pump fluence, increasing from 2.49 ± 0.11 ps to 3.28 ± 0.03 ps and 57.36 ± 11.28 ps to 164.96 ± 1.61 ps, respectively, as the pump fluence rises from 0.80 to 1.19 mJ/cm². The ~0.42 ps demagnetization timescale is consistent with that of 3d transition metals, indicating the transient magnetic response of the low-Gd-concentration heterostructure is dominated by the CoFe sublattice. Our findings validate that OPTE is an effective approach for the quantitative characterization of electron–lattice–spin coupling processes in spin-based heterostructures and provide critical experimental insights for controllable manipulation of ultrafast spin dynamics, laying a foundation for the design of ultrafast terahertz spintronic devices. Full article

The widespread presence of antibiotic residues in aquatic environments poses severe ecological risks. While photocatalytic oxidation offers a promising, eco-friendly remediation technology, developing stable and high-efficiency photocatalysts remains a significant challenge. This study investigates the synthesis of Bi₂O₃/TiO₂ heterojunction with tailored morphological structures to enhance the degradation of tetracycline (TC). A series of Bi₂O₃/TiO₂ photocatalysts were prepared via a solvothermal method using mixed alcohol solvents (ethylene glycol and ethanol) to regulate morphology. Comprehensive characterization was performed using XRD, BET, TEM, XPS, UV-Vis, and PL spectroscopy. Photocatalytic activity was evaluated by monitoring TC removal efficiency under light irradiation. The optimized catalyst of BT5-EG3 (n(Bi)/n(Ti) = 0.05; V(EG):V(ethanol) = 1:3) achieved the highest TC conversion of 93.9% within 120 min. This superior performance is attributed to a large specific surface area, abundant lattice oxygen, and a narrowed band gap of 2.52 eV, which significantly promoted the spatial separation of photogenerated charge carriers and suppressed their ultrafast recombination. The reaction followed pseudo-first-order kinetics, and the catalyst demonstrated excellent stability, providing a robust strategy for treating antibiotic-polluted water. Full article

Oxygenic and anoxygenic photosynthesis are initiated through the absorption of light by chlorophyll and bacteriochlorophyll photosynthetic pigments, respectively, which function as light-harvesting (antenna) and redox pigments on the photosynthetic membrane that trap and convert the absorbed optical energy into chemical energy. While several studies have characterized the ultrafast spectra, kinetics, and structures of the light-harvesting and reaction center complexes that contain the photosynthetic pigments, a detailed understanding of how the ultrafast excited-state dynamics vary across different photosynthetic pigments is lacking. Such information is critical in understanding the molecular mechanisms of both artificial and natural photosynthetic systems. In this study, we conducted ultrafast time-resolved absorption spectroscopy on chlorophyll and bacteriochlorophyll photosynthetic pigments at room temperature to directly compare the spectra and kinetics of their transient, excited electronic states formed following photon absorption. The recorded ultrafast spectral and kinetic data, spanning the femtosecond to sub-microsecond timescales, show interesting similarities and differences between these two distinct types of photosynthetic pigments. These experimental results help clarify the relationship between photosynthetic pigment structure and the resultant ultrafast processes in the oxygenic and anoxygenic photosynthetic reaction mechanisms. Full article

This study presents the synthesis and electrochemical characterization of meso-tetracyanobutadiene (TCBD)-functionalized diphenylporphyrin (DPP) complexes incorporating copper (Cu) and nickel (Ni) metals. These push–pull metallo diphenylporphyrin–TCBD complexes were synthesized via a [2 + 2] cycloaddition–retroelectrocyclization reaction between 5-bromo-15-formyl-10,20-diphenylporphyrin metal(II) complexes (M = Cu, Ni) and tributyl(phenylethynyl)stannate, followed by tetracyanoethylene (TCNE) addition. The resulting TCBD-functionalized porphyrins were obtained in moderate yields (70–75%) and thoroughly characterized by ¹H and ¹³C NMR, UV-Vis spectroscopy, MALDI-TOF-MS, and single-crystal XRD. Although the single-crystal X-ray structure of NiDPP was solved, DFT calculations were used to determine the structures of the donor–acceptor MDPP-TCBD systems and to visualize their electronic structures. HOMO on the porphyrin π system and LUMO on the TCBD entity were observed, and energy level diagrams clearly laid out the electron donor and acceptor parts of the molecular systems. As expected, these novel donor–acceptor porphyrinoid assemblies exhibited enhanced push–pull properties in both the ground and excited states. Femtosecond transient absorption studies revealed that both NiDPP-TCBD and CuDPP-TCBD populate the charge-transfer state upon photoexcitation, with lifetimes of 383.1 ps and 484.7 ps, respectively, in benzonitrile. The charge-transfer states populated the triplet or doublet states (in the case of CuDPP) before returning to the ground state. Full article

The attosecond (10⁻¹⁸ s) light pulse represents the fastest time scale currently mastered by the scientific community, which enables the observation of electron dynamics within atoms and molecules, offering powerful tools to probe chemical reaction mechanisms and advance research in photovoltaic materials and biological processes. In this work, we investigate the generation of visible attosecond optical pulses via spectral broadening in Hollow-Core Fiber (HCF), followed by coherent recombination using a Three-Channel Light Field Synthesizer (TCLFS). The influence of the input pulse duration on Group Delay Dispersion (GDD), Third-Order Dispersion (TOD), and spectral broadening is systematically analyzed. Furthermore, the effects of GDD, TOD, and the carrier–envelope phase (CEP) on waveform synthesis are quantitatively examined for the first time. These findings provide valuable insights into dispersion management strategies essential for developing high-quality visible attosecond light sources, paving the way for future applications in ultrafast spectroscopy and light field-driven electron dynamics. Full article

An ultrafast laser system combined with an optical delay line allowed ablation and in-scription at 1 kHz and 1 GHz pulse burst within transparent polyimide films. The two-photon-induced absorption results in clean surface ablation, while inscription results in polymer decomposition, creating carbonised regions within the polymer. Three pulse bursts at 1 GHz increased the observed coupling to the material significantly. Modified regions (with linewidths down to a few microns) were investigated using optical microscopy, white light interferometry, SEM and Raman spectroscopy, supporting the increasing carbon density relative to the pristine polymer. As depth of field was only a few microns at high NA, 3D micro-structuring was achieved. Polymer decomposition produces gaseous products, resulting in internal stress and thus affecting inscription fidelity. An inscribed subsurface electrode with dimensions of 5 mm × 0.3 mm × 3 μm connected to conducting vias had a resistance of R = 10.6 ± 0.2 kΩ, along with resistivity of ρ ~ 0.19 Ω cm; hence, it had DC conductivity, σ ~ 5.3 Scm⁻¹. This conductivity is similar to that of bulk graphite and could well form the basis of future flexible sensors, demonstrating single-step 3D subsurface inscription of carbon or laser-induced graphene structures. Full article

Topological 3D Dirac semimetals are characterized by bulk Dirac cone band crossings and nontrivial topological surface states, giving rise to a wealth of exotic physical properties and attracting considerable attention in recent years. Understanding the nonequilibrium dynamics of Dirac semimetals in micro-size provides critical guidance for the design of micro- and nanoscale optoelectronic and ultrafast photonic devices. In this work, we employ time-resolved microscopic transient spectroscopy to investigate the nonequilibrium photocarrier and lattice dynamics in microcrystalline Dirac semimetal NiTe₂, a prototypical 3D Dirac semimetal. Following photoexcitation at 390 nm, the transient reflectivity kinetics of NiTe₂ can be well described with a triple-exponential decay function. The fastest relaxation component occurs on a sub-picosecond timescale and increases with pump fluence, which originates from electron-optical phonon coupling. An intermediate relaxation process with a characteristic time of ~8 ps is attributed to electron–hole recombination, while a slower decay component on the order of ~20–30 ps can be assigned to the anharmonic decay of optical phonons into acoustic phonons. Polarization-resolved measurements reveal nearly in-plane isotropic transient responses, which are insensitive to the polarization of probe light. These findings contribute to the physical insights for the development of future photonics and optoelectronic devices based on topological Dirac semimetals. Full article

Lithium-ion batteries suffer from severe capacity fading and start-up failure at low temperatures owing to restricted Li⁺ transport and deteriorated interfacial kinetics. To enable rapid and safe activation under such conditions, this study designs a microwave-driven dual-layer leakage-proof composite phase-change module (EPG–BN–CF–PAG), comprising an epoxy–graphene–boron nitride outer encapsulation and a ceramic fiber–boron nitride porous inner scaffold that adsorbs a paraffin–graphene phase-change core. The synergy between the dense outer shell and the internal adsorption framework affords excellent shape stability, with an enthalpy retention exceeding 95% and no visible leakage after 20 heating–cooling cycles. Owing to the strong microwave-absorption capability of graphene, the module can be rapidly heated from −10 °C to ~60 °C within 60 s while establishing a homogeneous and stable temperature field. Combined simulations and experiments show that the module efficiently transfers heat to a lithium-ion cell, raising its temperature from −10 °C to ~30 °C within 60 s and thus bringing it into a practical operating window. Electrochemical impedance spectroscopy further reveals that the thermally induced activation markedly improves interfacial kinetics, reducing the bulk resistance from 500 Ω to 30 Ω and the charge-transfer resistance from 800 Ω to 30 Ω. This microwave-driven phase-change heating strategy features ultrafast response, excellent anti-leakage performance, and favorable thermal properties, providing an engineering-feasible thermal-management solution for the rapid cold start of lithium-ion batteries under extremely low-temperature conditions. Full article

We present a rapid, energy-efficient, and ecofriendly route for the synthesis of alkaline earth titanate perovskites—CaTiO₃, SrTiO₃, and BaTiO₃—using an affordable, commercially available CO₂ laser engraver, commonly found in makerspaces and small-scale workshops. The method involves direct laser irradiation of compacted pellets composed of low-cost, abundant, and non-toxic precursors: TiO₂ and alkaline earth carbonates (CaCO₃, SrCO₃, BaCO₃). CaTiO₃ and BaTiO₃ were synthesized with phase purities exceeding 97%, eliminating the need for conventional high-temperature furnaces or prolonged thermal treatments. X-ray diffraction (XRD) coupled with Rietveld refinement confirmed the formation of orthorhombic CaTiO₃ (Pbnm), cubic SrTiO₃ (Pm3⁻m), and tetragonal BaTiO₃ (P4mm). Raman spectroscopy independently corroborated the perovskite structures, revealing vibrational fingerprints consistent with the expected crystal symmetries and Ti–O bonding environments. All samples contained only small amounts of unreacted anatase TiO₂, while BaTiO₃ exhibited a partially amorphous fraction, attributed to the sluggish crystallization kinetics of the Ba–Ti system and the rapid quenching inherent to laser processing. Transmission electron microscopy (TEM) revealed nanoparticles with average sizes of 50–150 nm, indicative of localized melting followed by ultrafast solidification. This solvent-free, low-energy, and highly accessible approach, enabled by widely available desktop laser systems, demonstrates exceptional simplicity, scalability, and sustainability. It offers a compelling alternative to conventional ceramic processing, with broad potential for the fabrication of functional oxides in applications ranging from electronics to photocatalysis. Full article

Emerging research indicates that neuronal activity is maintained by an architectural system of protons in a multi-scale fashion. Proton architecture is formed when organelles (such as mitochondria, endoplasmic reticulum, lysosomes, synaptic vesicles, etc.) are coupled together to produce dynamic energy domains. Techniques have been developed to visualize protons in neurons; recent advances include near-atomic structural imaging of organelle interfaces using cryo-tomography and nanoscale resolution imaging of organelle interfaces and proton tracking using ultra-fast spectroscopy. Results of these studies indicate that protons in neurons do not diffuse randomly throughout the neuron but instead exist in organized geometric configurations. The cristae of mitochondrial cells create oscillating proton micro-domains that are influenced by the curvature of the cristae, hydrogen bonding between molecules, and localized changes in dielectric properties that result in time-patterned proton signals that can be used to determine the metabolic load of the cell and the redox state of its mitochondria. These proton patterns also communicate to the rest of the cell via hydrated aligned proton-conductive pathways at the mitochon-dria-endoplasmic reticulum junctions, through acidic lipid regions, and through nano-tethered contact sites between mitochondria and other organelles, which are typically spaced approximately 10–25 nm apart. Other proton architectures exist in lysosomes, endosomes, and synaptic vesicles. In each of these organelles, the V-ATPase generates steep concentration gradients across their membranes, controlling the rate of cargo removal from the lumen of the organelle, recycling receptors from the surface of the membrane, and loading neurotransmitters into the vesicles. Recent super-resolution pH mapping has indicated that populations of synaptic vesicles contain significant heterogeneity in the amount of protons they contain, thereby influencing the amount of neurotransmitter released per vesicle, the probability of vesicle release, and the degree of post-synaptic receptor protonation. Additionally, proton gradients in each organelle interact with the cytoskeleton: the protonation status of actin and microtubules influences filament stiffness, protein–protein interactions, and organelle movement, resulting in the formation of localized spatial structures that may possess some type of computational significance. At multiple scales, it appears that neurons integrate the proton micro-domains with mechanical tension fields, dielectric nanodomains, and phase-state transitions to form distributed computing elements whose behavior is determined by the integration of energy flow, organelle geometry, and the organization of soft materials. Alterations to the proton landscape in neurons (e.g., due to alterations in cristae structure, drift in luminal pH, disruption in the hydration-structure of the cell, or imbalance in the protonation of cytoskeletal components) could disrupt the intracellular signaling network well before the onset of measurable electrical or biochemical pathologies. This article will summarize evidence indicating that proton–organelle interaction provides a previously unknown source of energetic substrate for neural computation. Using an integrated approach combining nanoscale proton energy, organelle interface geometry, cytoskeletal mechanics, and AI-based multiscale models, this article outlines current principles and unresolved questions related to the subject area as well as possible new approaches to early detection and precise intervention of pathological conditions related to altered intracellular energy flow. Full article