Pulsed Laser Excitation Research Articles

A Cu(I)-Based MOF with Nonlinear Optical Properties and a Favorable Optical Limit Threshold.

The exploitation of high-performance third-order nonlinear optical (NLO) materials that have a favorable optical limit (OL) threshold is essential due to a rise in the application of ultra-intense lasers. In this study, a Cu-based MOF (denoted as Cu-bpy) was synthesized, and its third-order NLO and OL properties were investigated using the Z-scan technique with the nanosecond laser pulse excitation set at 532 nm. The Cu-bpy exhibits a typical rate of reverse saturable absorption (RSA) with a third-order nonlinear absorption coefficient of 100 cm GW-1 and a favorable OL threshold of 0.75 J cm-2 (at a concentration of 1.6 mg mL-1), which is lower than that of most NLO materials that have been reported on so far. In addition, a DFT calculation was performed and was in agreement with our experimental results. Furthermore, the mechanism of the third-order NLO properties was illustrated as one-photon absorption (1PA). These results investigate the relationship between the structure and the nonlinear optical properties of Cu-bpy, and provide an experimental and theoretical basis for its use in optical limiting applications.

Measurement of the 13S1→23S1 interval in positronium using field ionization of Rydberg states

We report a 40 parts per 109 measurement of the positronium 13S1→23S1 interval using pulsed two-photon optical spectroscopy. The transition is detected via field ionization of atoms excited from the 2S to the 20P Rydberg state. Precise Monte Carlo line-shape simulations allow for the accounting of effects such as Doppler and ac Stark shifts, while an optical heterodyne measurement of the excitation laser pulse is used to correct for laser frequency chirp. A value of 1233607210.5±49.6MHz is obtained. This scheme allows for the measurement of the velocity distribution of positronium atoms to correct for the second-order Doppler effect. This is a major source of systematic uncertainty expected for future measurements of this transition with a cw laser; thus, our technique paves the way toward a new generation of a high-precision determination of this interval in positronium. Published by the American Physical Society 2025

Unveiling the Influence of Hot Carriers on Photovoltage Formation in Perovskite Solar Cells

The experimental and theoretical study of photovoltage formation in perovskite solar cells under pulsed laser excitation at 0.53 μm wavelength is presented. Two types of solar cells were fabricated on the base of cesium-containing triple cation perovskite films: (1) Csx(FA0.83MA0.17)(1−x)Pb(I0.83Br0.17)3 and (2) Csx(FA0.83MA0.17)(1−x)Pb0.8Sn0.2(I0.83Br0.17)3. It is found that photovoltage across the solar cells consists of two components, U = Uph + Uf. The first one, Uph, is the traditional photovoltage arising due to laser radiation-induced electron-hole pair generation. The second one, Uf, is the fast component following the laser pulse and has a polarity opposite to that of Uph. It is shown that the fast photovoltage component results from the laser radiation-caused heating of free carriers. The transient photovoltage measurements show that the values of the fast component Uf are nearly the same in both types of perovskite solar cells. The magnitude of the traditional photovoltage of mixed Pb-Sn perovskite solar cells is lower than that of Pb-based cells.

FULLY ANALYTICAL SOLUTION FOR THE FIRST SPECTRAL MOMENT OF A FLUOROPHORE IN SOLUTION

One of the common methods for assessing the solvation dynamics of a fluorescent system in a polar medium is the analysis of the first spectral moment behavior. So there is a need to build a model that takes into account important physical processes and at the same time is not demanding in terms of calculations. In this paper, an approach is proposed that considers the parameters of the exciting laser pulse and intramolecular vibrational relaxation for constructing the solvation dynamics. A method for building an analytical solution for the dynamics of the first spectral moment is presented. This model is free of numerical methods using, and it is a simple construction built by basics functions and an additional error function. The influence of all key parameters on the system relaxation is illustrated. It is shown that delocalization in time of the pump pulse suppresses the oscillatory behavior of the first moment and hides information about the damped intramolecular mode. The similar effect is also observed with the diffusion and inertial processes contribution insreasion to the reorganization energy at early stages of relaxation. The presented model can be generalized to take into account quantum transitions between vibrational sublevels of high-frequency intramolecular vibrations.

An overview of the use of non-titanium MXenes for photothermal therapy and their combinatorial approaches for cancer treatment.

Since the initial publication on the first Ti3C2T x MXene in 2011, there has been a significant increase in the number of reports on applications of MXenes in various domains. MXenes have emerged as highly promising materials for various biomedical applications, including photothermal therapy (PTT), drug delivery, diagnostic imaging, and biosensing, owing to their fascinating conductivity, mechanical strength, biocompatibility and hydrophilicity. Through surface modification, MXenes can mitigate cytotoxicity, enhance biological stability, and improve histocompatibility, thereby enabling their potential use in in vivo biomedical applications. MXenes are also known for their ability to absorb light in the near-infrared (NIR) region and generate heat by localised surface plasmon resonance (LSPR) effects and electron-phonon coupling. Optical excitation laser pulses result in hot photocarrier distribution in MXenes, which quickly transfers surplus energy to the crystal lattice and results in the internal conversion of light into heat with nearly 100% efficiency. The relaxation of hot carrier distribution by electron-phonon interactions leads to the cooling of the lattice by dissipating thermal energy to the surrounding environment. This heating effect of MXenes makes them potential photothermal agents (PTAs), particularly for PTT applications. The adjustable surface of MXenes and their high surface area-to-volume ratios are ideal for the combinatorial approach of PTT along with drug delivery, photodynamic therapy (PDT), bone regeneration and other applications. Since non-Ti MXenes are more biocompatible than Ti MXenes, they are promising candidates for different biomedical applications. This comprehensive review provides a concise overview of the current research patterns, properties, and biomedical applications of non-Ti MXenes, particularly in PTT and its combinatorial approaches.

Super-Resolved Fluorescence Lifetime Imaging of Single Cy3 Molecules and Quantum Dots Using Time-Correlated Single Photon Counting with a Four-Pixel Fiber Optic Array Camera.

Time-resolved single molecule localization microscopy (TR-SMLM) with a 2 × 2 pixel fiber optic array camera was combined with time-correlated single photon counting (TCSPC) to obtain super-resolved fluorescence lifetime images of individual Cy3 dye molecules and individual colloidal CdSe/CdS/ZnS core/shell/shell semiconductor quantum dots (QDs). The characteristic blinking and bleaching behavior of the Cy3 and the blinking behavior of the QD emitters were used as distinguishing optical characteristics to isolate them and determine their centroid locations with spatial resolution below the optical diffraction limit. TCSPC was used to characterize the fluorescence lifetime and intensity corresponding to each emitter location. The mean centroid locations of the QDs could be determined with a precision of ∼1-4 nm, and the mean centroid locations of the Cy3 molecules could be determined with a precision of ∼2-9 nm, depending on the number of photons collected during the observation time. In a super-resolved fluorescence lifetime image with a single Cy3 dye molecule and a single QD separated by ∼34 nm, the two emitters were distinguished based on the average photon arrival times with respect to the excitation laser pulse observed during time intervals when only one emitter was in the on state, ∼6 ns for Cy3 and ∼17 ns for the QD. The mean distance between the two emitters was determined with a precision of ∼8 nm. The feasibility of using this super-resolved fluorescence lifetime imaging technique to investigate QD-dye complexes that use Förster resonance energy transfer (FRET) and/or electron transfer to form optical biosensors is discussed.

Mechanisms of Separation of the Elastic Step and the Thermal Step

AbstractThe elastic interaction causes a two‐step conversion from the low‐spin (LS) to the high‐spin state (HS) following a femtosecond laser pulse excitation. These steps occur on different timescales: a spin conversion (elastic step) in a short time due to pressure propagation and a late spin conversion (thermal step) resulting from heat diffusion. In this paper, we provide a brief review of models for spin crossover phenomena, emphasizing the role of the difference of degeneracy of the HS state and LS state and elastic interaction due to changes in local structures. We also review theoretical approaches to these effects. Additionally, to analyze the dynamical process of spin conversion after photo‐irradiation, it is necessary to consider mechanisms of heat transfer among spins. Recently, we proposed a two‐temperature model that incorporates both lattice and spin temperatures, which enables us to reproduce the two steps under an early uniformization of the lattice temperature, highlighting the importance of the timescales of these processes. Furthermore, we explore possible mechanisms to separate the two steps by examining the different timescales of processes of spin conversions by mechanical and entropic forces, and also by considering changes of local temperature due to spin conversion.

A novel hydrodynamic semiconductor model under Hall current effect and laser pulsed excitation

This paper presents a novel investigation into the effects of a strong external magnetic field on a hydro-poroelastic semiconductor model within the framework of photo-thermoelasticity theory in two dimensions. This study focuses on generating a Hall current and its impact on the coupled behavior of thermal, mechanical, and electronic fields in a semiconductor medium saturated with fluid. Using the normal mode analysis, we derive and analyze the wave propagation characteristics of key physical fields, including the non-dimensional temperature, displacement, mechanical stresses, carrier density, and excess pore water pressure, in response to the imposed magnetic field. Boundary conditions relevant to real-world applications are incorporated to assess the interactions between these fields. The results provide insight into the dynamic coupling of electromagnetic, thermal, and mechanical phenomena in porous semiconductor materials and offer potential applications in the design of magneto-sensitive semiconductor devices as well as in geophysical and biomedical engineering fields where such multi-field interactions are critical. The results obtained are plotted with some comparisons.

Photoremixing of Photosegregated Formamidinium/Cesium Lead Iodide/Bromide Thin Films under Pulsed Laser Excitation

Photoremixing of Photosegregated Formamidinium/Cesium Lead Iodide/Bromide Thin Films under Pulsed Laser Excitation

The substituent effect on pulsed laser beam self-action manifestation in azo-azomethine PMMA composites thin films in visible and near IR ranges

Efficiency of nonlinear optical response was studied for a set of azo-azomethines dyes with substituted electron-withdrawing/donating groups, being embedded in poly(methyl methacrylate) (PMMA) matrix, via self-action effects manifestation of mode-locked Nd:YAG laser single pulses in visible at 532 nm, and in near IR at 1064 nm ranges. Photoinduced variations of refractive index and optical absorption/bleaching are crucially dependent on electron-donating/accepting substituents' properties with |Re(χ(3))| ∼ 10−7 esu and |Im(χ(3))| ∼ 10−9 esu efficiencies correspondingly at moderate laser excitation up to 10 MW/cm2. Incorporation of the azomethine group has provided tendency for fractional self-focusing effect manifestation in visible range against reference Azo dye, while at 1064 nm – self-defocusing one. For some dyes magnitudes of |Re(χ(3))| in near IR range are comparable and even higher than for the corresponding ones at 532 nm due to resonant cascaded three photon excitation into the peak vicinity of π→π∗ transitions of the dyes. It was established linear relationship between second-order hyperpolarizabilities under pulsed and CW laser excitation in visible range, being preliminary irradiated within full spectra of UV lamp for CW laser diagnostics mode. It proofs a suggestion that picosecond range single pulses transfer dyes into the same excited state as full spectrum of a mercury lamp irradiation – conventional tool for the smart molecules’ isomerization. Analysis of the experimental data has shown a high potential for the azo-azomethines dyes doped polymer composites in nonlinear optical applications.

Charge Carrier Dynamics at the Perovskite Interface with Self-Assembled Monolayers.

Self-assembled monolayers (SAMs) deposited on the hole-collecting electrodes of p-i-n perovskite solar cells effectively replace bulky hole transporting layers. However, the mechanism by which monolayers control the electronic processes and how they depend on the properties of the monolayer molecules remain poorly understood. In this study, we developed a simplified perovskite solar cell imitator with blocked electron extraction to investigate the photocurrent dynamics between the perovskite and the hole-collecting ITO electrode. We investigated the photoluminescence and photovoltage dynamics under short laser pulse excitation and addressed the influence of bulky and monomolecular hole transport layers. Our findings reveal that the photovoltage dynamics is significantly affected by the properties of the transport and perovskite layers, which in turn depend on the methods of sample preparation and exploration. Photocurrent dynamics is determined by several processes, including charge carrier displacement in the local electric field, hole transport to ITO, trapping of holes in interface trap states, and electron-hole recombination at the interface. We propose a model that takes into account molecular dipole moments and their ionization potentials to partially explain the different influences of different monolayers on the hole extraction and interfacial recombination rates. Additionally, the photovoltage dynamics also strongly depends on the illumination of the sample and shows memory effects that persist over minutes and hours and are attributed to the redistribution of ions.

Growth of dendritic CuS nanostructures for photoacoustic image guided Chemo-Photothermal therapy

Herein, we report a unique method for design and development of carboxyl enriched dendritic CuS nanostructures (CuS NSs) for photoacoustic image guided chemo-photothermal therapy. The dendritic network was grown on the surface of CuS nanoparticles via layer-by-layer assembly of amino acid. XRD and TEM studies established the formation of crystalline well-spherical nanosized hexagonal covellite (CuS) phase. The successful growth of dendritic structure was apparent from the rise in surface charge, hydrodynamic diameter and characteristic vibrational band intensity of peptide bonds. The developed different generations of dendritic CuS NSs (D0-CuS NSs, D1-CuS NSs, D2-CuS NSs and D3-CuS NSs) displayed wide-ranging absorption band in near infrared (NIR) zone and exhibited good photothermal heating efficacy upon irradiation of 980 nm laser light. From in-vitro cellular studies, it has been found that the NIR irradiation effectively enhanced the photothermal toxicity of D3-CuS NSs towards cancer cells. Moreover, these negatively charged water-dispersible D3-CuS NSs were conjugated with positively charged anticancer drug, doxorubicin hydrochloride (DOX) through electrostatic interaction. The DOX loaded D3-CuS NSs (DOX@D3-CuS NSs) revealed pH dependent drug release behaviour and their considerable uptake in breast cancer cells (MCF-7). Further, DOX@D3-CuS NSs exhibited a much higher toxicity towards cancer cells upon NIR light over individual counterparts suggesting their strong ability for chemo-photothermal therapy. Moreover, these biocompatible CuS NSs have shown excellent concentration dependent photoacoustic properties at pulse laser excitation (850 nm) and thus, they can be found potential application in chemo-photothermal therapy.

High-spectral-resolution quantum Fourier-transform infrared spectroscopy with pulsed laser excitation

High-spectral-resolution quantum Fourier-transform infrared spectroscopy with pulsed laser excitation

Time-dependent configuration-interaction simulations for exciton-exciton fusion in perylene dimers after laser pulse excitation

Time-dependent configuration-interaction simulations for exciton-exciton fusion in perylene dimers after laser pulse excitation

Photothermal measurement of material properties for translucent thermal barrier coatings

In this study, a photothermal nondestructive method was proposed to measure the material parameters of semi-transparent or translucent thermal barrier coatings (TBCs). We derived a theoretical model for the photothermal signal from a two-layer semi-infinite material system with a translucent first layer after a pulse laser excitation. Its solution was verified by numerical solution. A data regression algorithm based on a least-squares fitting was used for the determination of the material parameters in the translucent first layer material. To verify this new method, an experimental system was set up with a pulse laser for thermal excitation and an infrared camera for image acquisition of the thermal emission transient from several translucent EBPVD TBC samples. The predicted coating thickness is consistent with the measured value by an optical microscope. The predicted thermal conductivity and optical attenuation coefficients in the absorption and emission band are found to be in good agreement with reference values.

Synthesis, Optical Spectroscopy, and Laser and Biomedical Imaging Application Potential of 2,4,6-Triphenylpyrylium Tetrachloroferrate and Its Derivatives.

Synthesis, optical spectroscopic properties, two-photon (TP) absorption-induced fluorescence, and laser and bioimaging application potentials of 2,4,6-triphenylpyrylium tetrachloroferrate (1),4-(4-methoxyphenyl)-2,6-diphenylpyrylium tetrachloroferrate (2), 2,6-bis(4-methoxyphenyl)-4-phenylpyrylium tetrachloroferrate (3), and 2,4,6-tris(4-methoxyphenyl)pyrylium tetrachloroferrate (4) are presented. The synthesis involves the conversion of pyrylium tosylates to pyrylium chlorides, followed by transformation into 1-4 on heating to reflux with FeCl3 in acetonitrile. They are characterized using 1H and 13C NMR spectra in CD3OD, and FTIR and Raman spectroscopic techniques. The salts dissolve in organic solvents and water (pH = 7 to 3) even at high concentrations (10-3 M). These solutions absorb light strongly from 500-300 nm. Solutions of 1, 3, and 4 fluoresce with high quantum yield in the 500-700 nm spectral range. Salts 1 and 4 exhibit fluorescence lifetime shortening, line width narrowing, and free-running laser action under intense pulsed laser excitation. Toxicity and cell imaging studies using human cancer cell lines reveal that salts 1 and 3 function as cellular fluorophores in vitro and have no adverse effects on cellular viability at nanomolar ranges. Furthermore, acetonitrile and methanol solutions of salts 1, 3, and 4 exhibit strong two-photon absorption-induced fluorescence, opening potential applications in biomedical imaging and microscopy.

Mid-infrared laser pulse excitation for terahertz generation from organic liquids molecules

Strong laser field is able to rotate gas molecules and the rotated gas molecules would emit electromagnetic waves when these molecules transition to the lower rotational energy levels. However, related investigation on liquid molecule rotation has not been reported, let alone the radiation falls in terahertz (THz) range. Here, a theoretical model is proposed to study the mid-infrared femtosecond laser driving organic liquid molecules such as methanol, ethanol, and acetic acid molecules to emit THz radiation. The interaction between laser electric field and liquid molecules are analyzed based on quantum mechanics theory. It is found that the spectrum of the THz radiation from methanol molecules range from 0.1 to 5 THz, while the spectra from ethanol and acetic acid molecules show nearly the same frequency range of 0.1–2 THz. These results indicate that broadband THz radiation can be generated through the transitions of rotational energy levels of the rotational liquid molecules excited by a linear polarization mid-infrared laser.

Micro/nano-scale transient thermo-viscoelastic responses for 1D temperature-dependent polymer-based rod heated by the ultra-short pulse laser based on nonlocal single-phase-lag heat conduction and Eringen’s differential elasticity

Micro/nano-scale transient thermo-mechanical responses are significantly important with rapid development and applications of ultra-short pulse in micro-machining of viscoelastic structure. This work aims to establish non-Fourier thermo-viscoelastic model based on nonlocal single-phase-lag heat conduction and Eringen’s differential elasticity. The developed model is applied to study thermo-viscoelastic responses for 1D temperature-dependent polymer-based rods subjected to non-Gaussian laser pulse excitation by Kirchhoff and Laplace transformation techniques. The results reveal that the parameters of the deformation, pulse laser, and nonlocal single-phase-lag heat conduction remarkably affect the wave propagations and thermo-viscoelastic response at micro/nano-scale nanoscale.

Photonic-Cavity-Enhanced Laser Writing of Color Centers in Diamond.

Color centers in diamond have widespread utility in quantum technologies, but their creation process remains stochastic in nature. Deterministic creation of color centers in device-ready diamond platforms can improve the yield, scalability, and integration. Recent work using pulsed laser excitation has shown impressive progress in deterministically creating defects in bulk diamond. Here, we extend this laser-writing process into nanophotonic devices etched into diamond membranes, including nanopillars and photonic resonators with writing and subsequent readout occurring in situ at cryogenic temperatures. We demonstrate the optically driven creation of carbon vacancy (GR1) and nitrogen vacancy (NV) centers in diamond nanopillars and observe enhanced photoluminescence collection from them. We also fabricate bullseye resonators and leverage their cavity modes to locally amplify the laser-writing field, yielding defect creation with picojoule write-pulse energies 100 times lower than those typically used in bulk diamond demonstrations.

Mediating coherent acoustic phonon oscillation of a 2D semiconductor/3D dielectric heterostructure by interfacial engineering

Abstract Coherent acoustic phonon (CAP) oscillation of 2D layered semiconductor/3D dielectric heterostructure generated by femtosecond laser pulse excitation can realize ultrafast photoacoustic conversion, while the photoacoustic conversion efficiency suffers from interfacial phonon scatterings of simultaneously laser-induced lattice heat. Here, taking advantage of graphene’s high thermal conductivity and large acoustic impedance, we demonstrate that phonon scatterings can be markedly mediated in a MoS$_2$/graphene/glass heterostructure via femtosecond laser pump-probe measurements. Equilibrium temperatures of MoS$_2$ lattice have been cooled down by about 45 %. As a benefit, both lifetime of CAP oscillations and pump pulse-picosecond acoustic pulse energy conversion efficiency have been enhanced by a factor of about 2. Our results constitute insights into CAP manipulations via interfacial engineering, that are fundamentally important for ultrafast photoacoustics based on 2D layered semiconductors.