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The temperature coefficient of resistivity (θ T) of carbon-based materials is a critical property that directly determines their electrical response upon thermal impulses. It could have metal- (positive) or semiconductor-like (negative) behavior, depending on the combined temperature dependence of electron density and electron scattering. Its distribution in space is very difficult to measure and is rarely studied. Here, for the first time, we report that carbon-based micro/nanoscale structures have a strong non-uniform spatial distribution of θ T. This distribution is probed by measuring the transient electro-thermal response of the material under extremely localized step laser heating and scanning, which magnifies the local θ T effect in the measured transient voltage evolution. For carbon microfibers (CMFs), after electrical current annealing, θ T varies from negative to positive from the sample end to the center with a magnitude change of >130% over <1 mm. This θ T sign change is confirmed by directly testing smaller segments from different regions of an annealed CMF. For micro-thick carbon nanotube bundles, θ T is found to have a relative change of >125% within a length of ∼2 mm, uncovering strong metallic to semiconductive behavior change in space. Our θ T scanning technique can be readily extended to nm-thick samples with μm scanning resolution to explore the distribution of θ T and provide a deep insight into the local electron conduction. [ABSTRACT FROM AUTHOR]

The article presents the estimation of temperature and emissivities of niobium and 100c6 steel around their melting points using techniques based on the minimization of the least squares norm or on Bayesian inference. Two models were considered for the spectral emissivity, including a linear variation with respect to the wavelength and independent spectral values. The measured data used for the solution of the parameter estimation problem were radiative fluxes collected from a five-wavelength pyrometer. The experimental apparatus used in this work was designed for the characterization of metal samples with sizes of few millimeters at high temperatures, combining aerodynamic levitation and laser heating. The use of the linear spectral emissivity model provided quite consistent results with the ordinary least squares estimator and with stochastic simulations using the Metropolis-Hastings algorithm. Similarly, the model of independent spectral emissivities resulted in accurate emissivities, but it required an informative prior for temperature, such as the known melting point of the metal sample. Therefore, whatever the inverse method used, a priori supplementary information in terms of emissivities or temperatures are needed due to the temperature-emissivity correlation and the unknow emissivity behavior. [ABSTRACT FROM AUTHOR]

Single-crystal germanium, as an excellent infrared optical material, has been widely applied in X-ray monochromators, night vision systems, and gamma radiation detectors. However, how to obtain high-quality optical lenses on their surfaces still faces challenges due to their hard and brittle properties. To this end, this paper proposes the in situ laser-assisted diamond turning (ILADT) process, which is the combination of a laser heating technique and a single-point diamond turning process. The in situ laser heating technique is employed to enhance the surface quality of the workpiece material, while the single-point diamond turning process is utilized to fabricate optical lenses. Experimental results showed that optical lenses with high surface quality were successfully machined. The profile error is 0.135 μm, indicating the high machining accuracy. The surface roughness Sa of the aspheric lens is 0.909 nm, indicating the high machining quality achieved by the proposed ILADT process. Therefore, this study provides an effective approach for producing high-quality optical lenses on single-crystal germanium surfaces, which holds great promise for future applications in the manufacturing of optical lenses with exceptional quality. [ABSTRACT FROM AUTHOR]

The thermal conductivity of bridgmanite, the primary constituent of the Earth's lower mantle, has been investigated using diamond anvil cells at pressures up to 85 GPa and temperatures up to 3,100 K. We report the results of time‐domain optical laser flash heating and X‐ray Free Electron Laser heating experiments from a variety of bridgmanite samples with different Al and Fe contents. The results demonstrate that Fe or Fe,Al incorporation in bridgmanite reduces thermal conductivity by about 50% in comparison to end‐member MgSiO3 at the pressure‐temperature conditions of Earth's lower mantle. The effect of temperature on the thermal conductivity at 28–60 GPa is moderate, well described as k=k300(300/T)a ${k={k}_{300}(300/T)}^{a}$, where a is 0.2–0.5. The results yield thermal conductivity of 7.5–15 W/(m × K) in the thermal boundary layer of the lowermost mantle composed of Fe,Al‐bearing bridgmanite. Plain Language Summary: Heat transport from the Earth's core and mantle to the surface drives plate tectonics and is crucial for sustaining the magnetic field which shields the surface from the solar wind. To quantify the heat transport process across the core‐mantle boundary layer, it is important to know thermal conductivity of major constituent minerals of the lower mantle in the region. Bridgmanite, which was called silicate perovskite, is the most abundant mineral in the lower mantle. Here we measured thermal conductivity on lab‐grown bridgmanite with different Fe and Al compositions compressed at the tips of two opposing diamonds to reproduce relevant pressures in the mantle. To obtain thermal conductivity, we applied optical and X‐ray Free Electron Lasers combined with optical spectroscopy and X‐ray diffraction to heat and measure time‐dependent temperature distributions of the sample. Our study provides relevant high pressure‐temperature data sets to better constrain the heat flux across the core‐mantle boundary. Key Points: We measured thermal conductivity of Fe,Al‐bearing bridgmanite, the most abundant mineral in the Earth's lower mantle, up to 85 GPa and 3,100 KFinite‐element calculations to temperatures obtained from laser flash and X‐ray Free Electron Laser heating measurements are fitted to evaluate temperature effect on conductivityWe assessed pressure, temperature, composition effects on thermal conductivity of bridgmanite at the thermal boundary layer of the lowermost mantle [ABSTRACT FROM AUTHOR]

Laser irradiation can induce local modulations of functional material properties, such as a decreased resistivity or a variation in reflectance. Recent studies investigated the laser-induced phase separation of 4 H-SiC into carbon and silicon on top of regrown SiC to customize its electrical conductivity for the application in electronic devices. To understand the physical processes leading to the laser-induced phase separation, time-resolved pump-probe measurements represent a suitable tool. This study advances the state of the art by characterizing the transient reflectance changes in 4 H-SiC upon irradiation by spatially resolved pump-probe reflectometry. Since the laser heating alters the reflectance of the sample, the spatially resolved measurement enables to observe the heat conduction from the irradiated to the non-irradiated areas, which sustains for several milliseconds. Numerical simulations of the temperature evolution reveal a restricted one-dimensional heat conduction into depth due to the broad lateral extent of the irradiated area. The associated sustained increased temperature within the irradiated area most certainly abets the feasibility of the phase separation. These findings offer practical insights for optimizing the applied laser parameters to tailor the material properties via phase separation. [ABSTRACT FROM AUTHOR]

Nanometre- to micrometre-sized solid dust particles play a vital role in star and planet formations. Despite of their importance, however, our understanding of physical and chemical properties of dust particles is still provisional. We have conducted a condensation experiment of the vapour generated from a solid starting material having nearly cosmic proportions in elements. A laser flash heating and subsequent cooling has produced a diverse type of nanoparticles simultaneously. Here we introduce four types of nanoparticles as potential dust particles in space: amorphous silicate nanoparticles (type S); core/mantle nanoparticles with iron or hydrogenized iron core and amorphous silicate mantle (type IS); silicon oxycarbide nanoparticles and hydrogenized silicon oxycarbide nanoparticles (type SiOC); and carbon nanoparticles (type C), all produced in a single heating–cooling event. Type IS and SiOC nanoparticles are new for potential astrophysical dust. The nanoparticles are aggregated to a wide variety of structures: compact, fluffy, and networked. A simultaneous formation of these nanoparticles, which are diverse in chemistry, shape, and structure, prompts a re-evaluation of astrophysical dust particles. [ABSTRACT FROM AUTHOR]

Multilayer core–shell microparticles with a liquid core and a polycomposite light-absorbing shell (microcapsules) are important components of modern bio- and medical technologies. Opening of the microcapsule shell and payload release can be realized by optical radiation. The photophoretic force is due to the radiation-stimulated thermal gradient and arises from the temperature inhomogeneity of the microparticle. Photophoretic forces, as well as radiation pressure forces, are inherently mechanical forces and can cause microcapsules to move during the opening cycle. We numerically simulate the microcapsule photophoretic motion when illuminated by an intense laser pulse. Numerical calculations of the temperature field in a spherical microcapsule are carried out using the finite element method, taking into account the auxiliary nanoparticles, which are randomly distributed around the capsule and serve to enhance the heating of the capsule under short pulse exposure. The spatial distribution of the absorbed optical power as well as the temporal dynamics of microcapsule heating depending of its size are investigated in detail. We show, for the first time to our knowledge, that under the joint action of light pressure and photophoretic forces, the microcapsule can move along the laser incidence direction both forward and backward at the distance of several tens of nanometers depending on the particle size and conditions of optical absorption. [ABSTRACT FROM AUTHOR]

With the advent of toroidal and double-stage diamond anvil cells (DACs), pressures between 4 and 10 Mbar can be achieved under static compression, however, the ability to explore diverse sample assemblies is limited on these micron-scale anvils. Adapting the toroidal DAC to support larger sample volumes offers expanded capabilities in physics, chemistry, and planetary science: including, characterizing materials in soft pressure media to multi-megabar pressures, synthesizing novel phases, and probing planetary assemblages at the interior pressures and temperatures of super-Earths and sub-Neptunes. Here we have continued the exploration of larger toroidal DAC profiles by iteratively testing various torus and shoulder depths with central culet diameters in the 30–50 µm range. We present a 30 µm culet profile that reached a maximum pressure of 414(1) GPa based on a Pt scale. The 300 K equations of state fit to our P–V data collected on gold and rhenium are compatible with extrapolated hydrostatic equations of state within 1% up to 4 Mbar. This work validates the performance of these large-culet toroidal anvils to > 4 Mbar and provides a promising foundation to develop toroidal DACs for diverse sample loading and laser heating. [ABSTRACT FROM AUTHOR]

AbstractSimulations on the interaction between laser pulses with materials during pulsed laser ablation require information on the characteristics of both laser and material. While details on material properties are extensively studied, the temporal profile of the laser source term is rarely studied and is generally assumed to be Gaussian. This article explores the effects of non-Gaussian temporal laser source terms (TLSTs) in simulating the heat diffusion within a metal upon irradiation of femtosecond pulsed lasers. We employed the Two-Temperature Model (TTM) to simulate the temperature evolution on the surface of copper upon irradiation of a 100-fs laser pulse with different TLSTs at different laser repetition modes (single-shot, burst, and biburst). We used a constant total fluence of 3J/cm 2 in all cases and subsequently calculated the ablation depths based on the resulting temperature values. Our results show that non-Gaussian TLSTs generate lower electron and lattice temperatures, resulting in shallower crater depths compared to a Gaussian TLST. However, under burst and biburst modes, particularly with higher subpulse number repetition time, the results of non-Gaussian TLSTs approximate those of Gaussian TLSTs. To initiate laser ablation in such cases, higher laser fluence might be required. Our work on non-Gaussian temporal profiles in TTM simulations can be applied to other computational methods in describing laser-matter interaction. [ABSTRACT FROM AUTHOR]

Specific features of thermal transformations of ferrocene Fe(C5H5)2 at a pressure of 10 GPa upon laser heating to 2200 K have been investigated in diamond anvil cells. Maps of the temperature distribution on the sample during the heating have been obtained. The structure and properties of the transformation products have been studied by X-ray diffraction analysis, transmission electron microscopy, and Mössbauer spectroscopy. It is established that a characteristic feature of ferrocene transformations upon laser heating is the simultaneous formation of nanoparticles of iron (α-Fe) and iron carbide (Fe7C3) crystalline phases. The presence of α-Fe in the products of thermal transformations of ferrocene at high pressures has been observed for the first time. Possible mechanisms of the simultaneous formation of these nanoparticles during ferrocene transformations are discussed. [ABSTRACT FROM AUTHOR]

The thermo-mechanical coupled behavior of biological tissues excited by a transient heating has been studied in this paper, in which the temperature-dependent physical properties are considered. A non-linear bio-thermo-mechanical coupled model with variable physical parameters has been proposed firstly in the context of the generalized theory with the dual-phase relaxation mechanism. An effective procedure constructed on an explicit finite difference scheme is then implemented to solve this non-linear model numerically. On this basis the thermo-mechanical coupled response and relative thermal damage within a skin tissue irradiated by a pulse laser has been explored. The temporal and spatial distributions of each physical field resulting from various cases have been obtained and illustrated. The results stated that the thermo-mechanical interaction induced by a laser heating would be inhibited by temperature-dependent physical parameters and this inhibition is more significant on the tissue displacement and normal stresses than tissue temperature. The thermal damage is also inhibited when the temperature dependence is considered and the time that healthy tissues can be tolerated would be a larger extension for its accumulative effect with tissue temperature. [ABSTRACT FROM AUTHOR]

Ultrashort pulse laser processed sulfur hyperdoped black silicon represents a promising silicon-based material for infrared optoelectronic applications due to its high sub-bandgap optical absorptance. Non-thermal melting and resolidification processes associated with such laser processing, however, result in amorphous and polycrystalline phases which may be detrimental for this purpose. Furthermore, the sulfur impurities are electrically inactive, impeding the formation of a rectifying junction. This work demonstrates an ultrafast laser heating process based on heat accumulation with laser pulses of 10 ps pulse duration at high repetition rates of 41 MHz and peak fluences between 33% and 66% of the ablation threshold as a method to (i) recrystallize the material and (ii) electrically activate the sulfur dopants while (iii) maintaining the sub-bandgap absorption. Furthermore, laser heating recovers the optical activity of sulfur states that have been previously deactivated by thermal annealing. The demonstrated process can have versatile applications in material functionalization due to its highly localized heat input accompanied by high cooling rates. [ABSTRACT FROM AUTHOR]

In this study, we report the synthesis of a new cubic neodymium-rhenium metallic alloy NdRe2 through the utilization of high pressure and laser heating in a diamond anvil cell. NdRe2 crystallizes in the … space group with a lattice parameter equal to 7.486 (2) Å and Z = 8 at 24 (1) GPa and 2,200 (100) K. It was studied using high-pressure single-crystal X-ray diffraction. The compound crystallizes in the cubic MgCu2 structure type. Its successful synthesis further proves that high-pressure high-temperature conditions can be used to obtain alloys holding a Laves phase structure. Ab initio calculations were done to predict the mechanical properties of the material. We also discuss the usage of extreme conditions to synthesize and study materials present in the nuclear waste. [ABSTRACT FROM AUTHOR]

The macrosegregation evolution kinetics of undercooled Cu60Fe40 immiscible alloy during slow cooling and rapid cooling processes were investigated by laser heating and glass fluxing techniques. The critical undercooling for the occurrence of metastable phase separation (MPS) was determined as 41 K. As the undercooling rised, MPS always occurred even if the undercooling rised to the largest value of 482 K (0.28 TL) and the nucleation temperature of primary phase was below the peritectic temperature for the first time. Meanwhile, both the phase separation time and the volume fraction of Fe-rich zone gradually increased under the two conditions. However, the phase separation time and the volume fraction of Fe-rich zone under the laser heating condition were much smaller than that under the glass fluxing state. At slight undercoolings, MPS preferentially happened at the bottom region of laser-heated sample and glass-fluxed sample, and the microstructure in other regions appeared as well-defined αFe dendrites in the (Cu) matrix phase. In highly undercooled state, macrosegregation morphologies composed of floating Fe-rich zones and sinking Cu-rich zones were preserved. The critical undercooling for the macrosegregation formation of glass-fluxed sample was relatively larger. Moreover, the Fe-rich zone completely floated to the top of glass-fluxed sample while that located in the middle region of laser-heated sample. The higher the bulk undercooling, the lower the lattice constant of (Cu) phase and the greater the lattice constant of αFe phase. The calculations and analyses of temperature field and fluid dynamics demonstrated that the difference of heat transfer mechanisms between laser-heated sample and glass-fluxed sample was responsible for the distinctions of macrosegregation evolution kinetics in the two experiments. [ABSTRACT FROM AUTHOR]

Stimuli-responsive polymers are an important class of materials with many applications in nanotechnology and drug delivery. The most prominent one is poly-N-isopropylacrylamide (PNIPAm). The characterization of the kinetics of its change after a temperature jump is still a lively research topic, especially at nanometer-length scales where it is not possible to rely on conventional microscopic techniques. Here, we measured in real time the collapse of a PNIPAm shell on silica nanoparticles with megahertz x-ray photon correlation spectroscopy at the European XFEL. We characterize the changes of the particles diffusion constant as a function of time and consequently local temperature on sub-microsecond timescales. We developed a phenomenological model to describe the observed data and extract the characteristic times associated to the swelling and collapse processes. Different from previous studies tracking the turbidity of PNIPAm dispersions and using laser heating, we find collapse times below microsecond timescales and two to three orders of magnitude slower swelling times. [ABSTRACT FROM AUTHOR]

Recently, there has been a high demand for elucidating kinetics and visualizing reaction processes under extreme dynamic conditions, such as chemical reactions under meteorite impact conditions, structural changes under non-equilibrium conditions, and in situ observations of dynamic changes. To accelerate material science studies and Earth science fields under dynamic conditions, a submillisecond in situ X-ray diffraction measurement system has been developed using a diamond anvil cell to observe reaction processes under rapidly changing pressure and temperature conditions replicating extreme dynamic conditions. The development and measurements were performed at the high-pressure beamline BL10XU/SPring-8 by synchronizing a high-speed hybrid pixel array detector, laser heating and temperature measurement system, and gas-pressure control system that enables remote and rapid pressure changes using the diamond anvil cell. The synchronized system enabled momentary heating and rapid cooling experiments up to 5000 K via laser heating as well as the visualization of structural changes in high-pressure samples under extreme dynamic conditions during high-speed pressure changes. [ABSTRACT FROM AUTHOR]

The effects of subsonic plasma flows of carbon dioxide and pure nitrogen combined with additional laser irradiation on silicon carbide material were investigated. Silicon carbide samples were exposed to temperatures from 1480 to 1620°C (in the carbon dioxide plasma flow) and from 1600 to 1960°C (in the pure nitrogen plasma flow) at a constant pressure in the test chamber of 1 × 104 Pa and gas mass flow rate of 2.4 g/s. Significant differences in the heat transfer and behavior of the samples were observed depending on the plasma composition. The microstructure and surface profiles of the samples before and after different exposures were compared. Surface peculiarities were detected in the areas where the maximum laser irradiation intensity was applied. [ABSTRACT FROM AUTHOR]

The effects of heat treatment with continuous laser radiation on samples of the Fe–18Cr–10Ni alloy of the austenitic-martensitic class that have undergone preliminary megaplastic torsional deformation in the Bridgman chamber are investigated. It is established that the combined application of deformation (deformation in the Bridgman chamber) and thermal (laser heating) effects to the alloy forms the structure of metastable austenite (γ phase), which differs from stable austenite in higher strength characteristics. The nature of this phenomenon is discussed. [ABSTRACT FROM AUTHOR]

Two-dimensional nanomaterials have obvious advantages in thermoelectric device development. It is rare to use the same experimental system to accurately measure multiple thermoelectrical parameters of the same sample. Therefore, scholars have developed suspended microdevices, T-type and H-type methods to fulfill the abovementioned requirements. These methods usually require a direct-current voltage signal to detect in Seebeck coefficient measurement. However, the thermoelectric potential generated by the finite temperature difference is very weak and can be easily overwritten by the direct-current voltage, thereby affecting the measurement accuracy. In addition, these methods generally require specific electrodes to measure the thermoelectric potential. We propose a measurement method that combines laser heating with an H-type device. By introducing a temperature difference in two-dimensional materials through laser heating, the thermoelectric potential can be accurately measured. This method does not require specific electrodes to simplify the device structure. The thermoelectrical parameters of supported graphene are successfully measured with this method; the results are in good agreement with the literature. The proposed method is unaffected by material size and characteristics. It has potential application value in the characterization of thermoelectric physical properties. [ABSTRACT FROM AUTHOR]

The field of nanowire (NW) technology represents an exciting and steadily growing research area with applications in ultra-sensitive mass and force sensing. Existing detection methods for NW deflection and oscillation include optical and field emission approaches. However, they are challenging for detecting small diameter NWs because of the heating produced by the laser beam and the impact of the high electric field. Alternatively, the deflection of a NW can be detected indirectly by co-resonantly coupling the NW to a cantilever and measuring it using a scanning probe microscope. Here, we prove experimentally that co-resonantly coupled devices are sensitive to small force derivatives similar to standalone NWs. We detect force derivatives as small as 10−9 N/m with a bandwidth of 1 Hz at room temperature. Furthermore, the measured hybrid vibration modes show clear signatures of avoided crossing. The detection technique presented in this work verifies a major step in boosting NW-based force and mass sensing. Flexural oscillations of singly-clamped nanowires can be detected by interferometry for diameters above 50 nm, while below such diameter the detection becomes challenging. The authors detect force derivatives as small as 10-9 N/m at room temperature by measuring hybrid vibration modes originated by coupling a nanowire and a cantilever. [ABSTRACT FROM AUTHOR]

Boron particles in solid-fuel ramjet combustion chambers typically exist in agglomerated form, and the gas composition within the chamber includes not only air but also propellant combustion products such as water vapor and CO2. This study investigates the thermal behavior, laser heating characteristics, and condensed-phase heating products of boron agglomerates in six distinct atmospheres: N2, O2, air, water vapor, CO2, and Ar. Thermal oxidation tests revealed that the reaction between boron and O2 dominates in an air atmosphere, while boron can still react with N2 in air to form granular boron nitride. Laser-induced heating resulted in ejection phenomena occurring in boron agglomerates when subjected to N2, air, water vapor, Ar, or O2 atmospheres, with the O2 atmosphere being the most conducive, exhibiting an average of 47 occurrences for individual agglomerates. The ejection process and frequency were found to be comparable in the air, Ar, and water vapor atmospheres, with an average ejection frequency ranging from 7 to 11 times. Although the ejection phenomenon occurred in the N2 atmosphere, its frequency was low, with an average of only two occurrences. Agglomerates underwent significant expansion before ejection, while single-particle boron did not exhibit ejection or expansion in any of these atmospheres. The highest surface temperatures of boron agglomerates upon laser heating in air, water vapor, N2, and Ar atmospheres were 2697.7 K, 2416.2 K, 2408.9 K, and 2392.1 K, respectively. Analysis of condensed-phase heating products revealed that boron agglomerates reacted with N2 or CO2 to form boron nitride or boron carbide, respectively. [ABSTRACT FROM AUTHOR]

The expansion and collapse of a cavitation bubble during laser heating and subcooled boiling of water in the vicinity of the tip of an optical fiber (laser heating element) installed in a water-filled glass tube with two open ends is studied experimentally and numerically. Cavitation, initiated by continuous laser radiation, is accompanied by the pushing and pulling movement of the heated liquid in the tube and outside it. For the first time, it has been shown that in a tube with an installed laser heating element in a liquid flow moving behind the walls of the bubble, when it collapses at the pole of the bubble surface remote from the end, a liquid jet appears, directed through the bubble to the end of the optical fiber. The jet speeds up the process of sucking liquid into the tube. [ABSTRACT FROM AUTHOR]

Time-domain thermoreflectance (TDTR) is a well-established pump–probe method for measuring thermal conductivity and interface conductance of multilayers. Interpreting signals in a TDTR experiment requires a thermal model. In standard front/front TDTR experiments, both pump and probe beams typically irradiate the surface of a multilayer. As a result, existing thermal models for interpreting thermoreflectance experiments assume that the pump and probe beams both interact with the surface layer. Here, we present a frequency-domain solution to the heat-diffusion equation of a multilayer in response to nonhomogeneous laser heating. This model allows analysis of experiments where the pump and probe beams irradiate opposite sides of a multilayer. We call such a geometry a front/back experiment to differentiate such experiments from standard TDTR experiments. As an example, we consider a 60nm amorphous Si film. We consider how signals differ in a front/front vs front/back geometry and compare thermal model predictions to experimental data. [ABSTRACT FROM AUTHOR]

This work reports results on the simultaneous spectroscopy of the specific heat and thermal expansivity of glycerol by making use of a wideband time-resolved thermal lens (TL) technique. An analytical model is presented which describes TL transients in a relaxing system subjected to impulsive laser heating. Experimentally, a set of TL waveforms, from 1 ns to 20 ms, has been recorded for a glycerol sample upon supercooling, from 300 to 200 K. The satisfactory fitting of the TL signals to the model allows the assessment of relaxation strength and relaxation frequency of the two quantities up to sub-100 MHz, extending the specific heat and thermal expansion spectroscopy by nearly three and eight decades, respectively. Fragility values, extracted from the relaxation behavior of the specific heat and the thermal expansion coefficient, are found to be similar, despite a substantial difference in relaxation strength. [ABSTRACT FROM AUTHOR]

We report the P-V-T equation of state measurements of B4C to 50 GPa and approximately 2500 K in laser-heated diamond anvil cells. We obtain an ambient temperature, third-order Birch–Murnaghan fit to the P-V data that yields a bulk modulus K0 of 221(2) GPa and derivative, (dK/dP)0 of 3.3(1). These were used in fits with both a Mie–Grüneisen–Debye model and a temperature-dependent, Birch–Murnaghan equation of state that includes thermal pressure estimated by thermal expansion (α) and a temperature-dependent bulk modulus (dK0/dT). The ambient pressure thermal expansion coefficient (α0 + α1T), Grüneisen γ(V) = γ0(V/V0)q and volume-dependent Debye temperature, were used as input parameters for these fits and found to be sufficient to describe the data in the whole P-T range of this study. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'. [ABSTRACT FROM AUTHOR]

The features of oxidation of ultra-high-temperature ceramic material HfB2-30 vol.%SiC modified with 1 vol.% graphene as a result of supersonic flow of dissociated CO2 (generated with the use of high-frequency induction plasmatron), as well as under the influence of combined heating by high-speed CO2 jets and ytterbium laser radiation, were studied for the first time. It was found that the addition of laser radiation leads to local heating of the central region from ~1750 to ~2000–2200 °C; the observed temperature difference between the central region and the periphery of ~300–550 °C did not lead to cracking and destruction of the sample. Oxidized surfaces and cross sections of HfB2-SiC-CG ceramics with and without laser heating were investigated using X-ray phase analysis, Raman spectroscopy and scanning electron microscopy with local elemental analysis. During oxidation by supersonic flow of dissociated CO2, a multilayer near-surface region similar to that formed under the influence of high-speed dissociated air flows was formed. An increase in surface temperature with the addition of laser heating from 1750–1790 to 2000–2200 °C (short term, within 2 min) led to a two to threefold increase in the thickness of the degraded near-surface area of ceramics from 165 to 380 microns. The experimental results indicate promising applications of ceramic materials based on HfB2-SiC as part of high-speed flying vehicles in planetary atmospheres predominantly composed of CO2 (e.g., Venus and Mars). [ABSTRACT FROM AUTHOR]

Combining experimental set up and ab initio molecular dynamics simulations, we were able to follow the time evolution of the X-ray absorption near edge spectrum (XANES) of a dense copper plasma. This provides a deep insight into femtosecond laser interaction with a metallic copper target. This paper presents a review of the experimental developments we made to reduce the X-ray probe duration, from approximately 10 ps to fs duration with table-top laser systems. Moreover, we present microscopic scale simulations, performed with Density Functional Theory, as well as macroscopic simulations considering the Two-Temperature Model. These tools allow us to get a complete picture of the evolution of the target at a microscopic level, from the heating process to the melting and expansion stages, with a clear view of the physics involved during these processes. This article is part of the theme issue 'Dynamic and transient processes in warm dense matter'. [ABSTRACT FROM AUTHOR]

Ochratoxin A (OTA) is a widespread mycotoxin that causes contamination in a variety of foodstuffs and environments, inducing great health risks to humans and animals. Rapid and sensitive detection of OTA is necessary for food safety, environmental health, and risk assessment. Herein, we report an aptamer microscale thermophoresis (MST) assay for OTA, with the unique merits of ratiometric analysis, rapid measurement, simple operation, high sensitivity, low sample consumption, and high throughput. A fluorescein (FAM)-labeled high-affinity DNA aptamer with a G-quadruplex and duplex structure was used as the recognition element for OTA, and MST, which measures the fluorescence responses of the sample solution inside capillaries to a mild temperature increase generated by infrared laser heating, was employed for signal generation. Upon OTA binding, the FAM-labeled aptamer probe underwent changes in conformation and stability, and the bound and unbound aptamer probes showed significant differences in their MST signals. To achieve sensitive detection of OTA with a large signal change, we systematically characterized aptamers with different stem lengths, which had large effects on the MST responses of the aptamer probes to OTA. We found that a 32-mer aptamer with FAM label at the 3′ end gave a sensitive MST response to OTA, allowing OTA detection within seconds with a detection limit of 0.98 nM under optimal experimental conditions. This aptamer MST assay shows potential in real sample analysis and broad applications. [ABSTRACT FROM AUTHOR]

This paper studies the effect of the laser melting process (LMP) on the microstructure and hardness of a new modified AlCuMgMn alloy with zirconium (Zr) and Yttrium (Y) elements. Homogenized (480 °C/8 h) alloys were laser-surface-treated at room temperature and a heating platform with in situ heating conditions was used in order to control the formed microstructure by decreasing the solidification rate in the laser-melted zone (LMZ). Modifying the AlCuMgMn alloy with 0.4 wt% Zr and 0.6 wt% Y led to a decrease in grain size by 25% with a uniform grain size distribution in the as-cast state due to the formation of Al3(Y, Zr). The homogenization dissolved the nonequilibrium intermetallic phases into the (Al) matrix and spheroidized and fragmentized the equilibrium phase's particles, which led to the solidification of the crack-free LM zone with a nonuniform grain structure. The microstructure in the LMZ was improved by using the in situ heating approach, which decreased the temperature gradient between the BM and the melt pool. Two different microstructures were observed: ultrafine grains at the boundaries of the melted pool due to the extremely high concentration of optimally sized Al3(Y, Zr) and fine equiaxed grains at the center of the LMZ. The combination of the presence of ZrY and applying a heating platform during the LMP increased the hardness of the LMZ by 1.14 times more than the hardness of the LMZ of the cast AlCuMgMn alloy. [ABSTRACT FROM AUTHOR]

The heat transfer to a cylindrical water-cooled copper model was experimentally investigated in an induction VGU-4 high-frequency (HF) plasmatron of the Institute for Problems in Mechanics of the Russian Academy of Sciences. The model, 30 mm in diameter, equipped with a calorimetric transducer with a heat-adsorbing graphite surface, 13.8 mm in diameter, was exposed to the surface heating in the combined regime by nitrogen plasma and laser radiation and in the cases of the heating with only laser radiation or a nitrogen plasma jet. The experiments in the HF-plasmatron jets were performed at the pressure in the setup low-pressure chamber p = 1 × 104 Pa, nitrogen mass flow rate G = 2.4 g/s, and the plasmatron HF-generator anode power Na.p. = 22 kW. It is established that in the chosen experimental regimes the dissociated-nitrogen jet and the high-frequency induction discharge do not produce a considerable effect on the laser beam passing through them. The values of the heat flux density are obtained as functions of the laser radiation power delivered. The subsonic nitrogen plasma flow in the quartz discharge channel and in the low-pressure chamber of the VGU-4 setup is numerically modeled under the experimental conditions basing on the solution of the complete Navier–Stokes equations using the Patankar–Spalding method. [ABSTRACT FROM AUTHOR]

In this paper, a thermal–mechanical–oxidation coupling experimental system based on laser heating is developed, containing two modes of Gaussian and flat-top lasers, which has a series of advantages such as high temperature range, rapid heating rate, and convenient observation. The system adopts active illumination and an optical filter to solve the problem where it is difficult for traditional digital-image correlation technology to image clearly under laser heating. A biaxial mechanical test machine is used to simulate the complex load by applying biaxial tension or compression loads on the material. Combined with the radiation temperature measurement and controllable flow field device, the thermal-mechanical-oxygen coupling experiment of high temperature resistant materials under aerobic environment can be carried out. The maximum uniform heat flux output density is 27.2 kW/cm2, and the maximum Gaussian heat flux output density is 105 kW/cm2. The thermal-mechanical-oxygen coupling experimental system and method are of great significance to the development of new high temperature resistant materials and thermal barrier coatings. [ABSTRACT FROM AUTHOR]

Through a series of high-pressure x-ray diffraction experiments combined with in situ laser heating, we explore the pressure–temperature phase diagram of germanium (Ge) at pressures up to 110 GPa and temperatures exceeding 3000 K. In the pressure range of 64–90 GPa, we observe orthorhombic Ge-IV transforming above 1500 K to a previously unobserved high-temperature phase, which we denote as Ge-VIII. This high-temperature phase is characterized by a tetragonal crystal structure, space group I4/mmm. Density functional theory simulations confirm that Ge-IV becomes unstable at high temperatures and that Ge-VIII is highly competitive and dynamically stable at these conditions. The existence of Ge-VIII has profound implications for the pressure–temperature phase diagram, with melting conditions increasing to much higher temperatures than previous extrapolations would imply. [ABSTRACT FROM AUTHOR]

The combination of laser irradiation heating and synchrotron X-ray sources has made it possible to observe the fiber-structure development that occurs at sub-millisecond timescales after necking during continuous drawing. Through wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) analysis of poly(ethylene terephthalate) fibers of three different molecular weights drawn under equivalent stresses, a good correlation was observed between the d-spacing of smectic (001ʹ) diffraction extrapolated to the necking point and the strength of the drawn fiber. This indicates that the molecular chains that bear the drawing stress also bear most of the applied stress during tensile testing of the resultant fiber. In addition, considering the drawing-stress dependence of the d-spacing and the molecular weight distribution of the fiber revealed that molecular chains with molecular weights over 23,000 g/mol bear the majority of tensile force applied to the fiber. [ABSTRACT FROM AUTHOR]

An experimental installation for laser heating (ULN-1) has been developed to implement a technique for identifying mathematical models of radiative-conductive heat transfer without using contact measurements. A substantiation of the choice of the system components and of the procedure for its application is given. Approbation of the installation and of the identification technique was carried out on the example of determining the thermophysical characteristics of a thin plate made of an opaque material. [ABSTRACT FROM AUTHOR]

Three different types of TiO2 nanoparticles in anatase and rutile phases were subject to nanosecond 532‐nm laser pulses in aqueous solution for enhanced reactivity in photocatalytic applications. Color changes observed during the laser processes resulted from laser pulse‐induced heating of TiO2 surfaces to form surface disorder with surface defects. Interestingly, TiO2 nanoparticles with different size and bulk phases undergo different changes in surface morphology, bulk phase, and defect density under the same laser pulses. The results are related with the differences in the absorption by initial defects on the TiO2 surface. Our results show that the type and density of initial defects within TiO2 matrix are important in determining subsequent thermal equilibrium‐driven changes. It is suggested that nanosecond laser pulses with energies lower than the bandgap of the semiconductor materials provide a chance for selective modification of oxide nanomaterials such as TiO2 for a new photoresponsive functionality in diverse applications. [ABSTRACT FROM AUTHOR]

Threshold properties and pulsed output of AlGaInP visible-emitting lasers with an asymmetric waveguide structure and a bulk active layer are analysed. The effects of the current leakage, increased by the heating of the laser due to the proximity of the electrical pulse source and the Joule heating in and around this source are analysed. When optimising the laser design, waveguiding properties of the bulk active layer are shown to be important, leading to threshold currents decreasing, and injection efficiency increasing, with active layer thickness in lasers with moderately thick (< 0.1 μm) active layers. [ABSTRACT FROM AUTHOR]

Double layers of deuterated and hydrogenated amorphous silicon (a‐Si:H) on glass are heated in the ambient by scanning with a green (532 nm) continuous wave laser. The hydrogen diffusion length in the laser spot is obtained from the deuterium (D)–hydrogen (H) interdiffusion measured by secondary ion mass spectrometry (SIMS), the temperature in the laser spot is obtained by calculation. Under certain conditions, detachment of the deuterated layer from the hydrogenated layer is observed in the SIMS depth profiles, visible by rising oxygen and carbon signals at the D/H interface attributed to in‐diffusion of atmospheric gas species like water vapor, oxygen, and carbon oxide. Stacks involving both undoped and boron‐doped a‐Si:H films show disintegration. The results suggest that the parameters leading to the disintegration effects are the presence of a plane of reduced material cohesion at the D/H interface, a sizeable H diffusion length and a rather high heating rate. Herein, it is likely considered that the observed layer disintegration process is involved in the peeling of a‐Si:H films upon fast heating. Furthermore, the results show that rapid laser heating can be used to detect planes of reduced material cohesion which may compromise the electronic properties of a‐Si:H‐based stacks. [ABSTRACT FROM AUTHOR]

An improved dual-phase-lagging model which reflects size effects caused by nanostructures is utilized to investigate the 2-D thermal conduction of nanosilicon films irradiated by ultrafast laser. The integral transformation method is used to solve the conduction governing equation based on the improved dual-phase-lagging model. The variation of the internal temperature along the thickness direction and the radial direction of the thin film is analyzed. We find that the temperature increases rapidly in the heated region of the film, and as time goes by, the energy travels from the heated end to another end in a form of wave. Although both the improved dual-phase-lagging model and the dual-phase-lagging model can obtain similar thermal wave temperature fields, the temperature distribution in the film obtained by the improved dual-phase-lagging model is relatively flat, especially for high Knudsen number. Under the same Knudsen number, the temperature obtained by the 2-D improved dual-phase-lagging model is higher than that obtained by the 1-D model, and the temperature difference becomes larger and larger as time elapses. [ABSTRACT FROM AUTHOR]

During pulsed laser-assisted manufacturing, the extremely high-temperature gradient in space will lead to very high-stress waves that play a critical role in structuring. Both shear and normal stress waves emerge in space. This work provides a review and perspective based on our past work spanning theoretical analysis, 1D molecular dynamics (MD) modeling, 3D MD modeling, and experimental characterization. Discussions are given on the non-Fourier effect during ultrafast laser-material interaction, stress-induced structural defects in recrystallization, and ablation confinement by ambient gas and nanotip during nanotip-assisted near-field nanomanufacturing. The presence of stress waves in space could cause permanent and temporary damages, and these damages are more caused by the shear stresses than the normal ones where the compressive component usually is much stronger than the tensile part. Due to the fact of very fast stress waves propagation and slow cooling and solidification, it is very challenging to conduct MD modeling of the entire domain even using stage-of-the-art parallel computation. Hybrid modeling that combines MD and macroscale modelings provides a better choice to tackle this problem. Time-resolved ultrafast temperature and stress characterization are still highly needed to provide deep physics understanding of laser-material interaction toward process control and optimization. [ABSTRACT FROM AUTHOR]

3D printing of continuous fiber reinforce plastics (CCFRP) with fused deposition modeling is a burgeoning manufacturing method because of its exceptional mechanical properties. Nevertheless, it cannot manufacture parts at high speeds. Using laser heating instead of the traditional resistive heating in 3D printing of CCFRP has the potential to improve printing speed owing to its high heating efficiency. In this article, a process of laser‐assisted rapid 3D printing of CCFRP is proposed. The heating process of CCFRP by laser is analyzed and verified. The linear relation between printing speed and laser power is established. The experiments demonstrate that the printing speed is increased to 30 mm/s with the laser. The mechanical properties of printed parts, though enhanced as the printing speed and laser power increase, are better than those obtained by traditional methods. Scanning electron microscope images and experiments reveal that proper laser power is conducive to the melting of plastics, strengthening interlayer bonding, and reducing voids under roller pressure. Nonetheless, excessive laser power ablates the plastic, resulting in increased voids. [ABSTRACT FROM AUTHOR]

To improve the processibility of high-volume fraction SiC p /Al composites and reduce the surface defects after machining, a machining method of laser-ultrasonic vibration assisted machining (L-UVAM) were presented in this paper. Aiming to study the mechanism of material deformation and surface formation in L-UVAM, a finite element model (FEM) of L-UVAM was developed and the corresponding experiments were conducted. The results combined simulation and experiments revealed that particle fracture, interface failure and crack propagation were the main forms of material deformation, and the support of the matrix for particles was weakened because of the softening effect caused by laser heating, which makes it easier for the tool to push particles distribution along the shear plane. In addition, the failure of the particles depended on its relative position to the tool. Compared with traditional machining, the surface quality of L-UVAM was better, and there were fewer broken particles and defects in the processed surface. The results obtained by simulation are in close agreement with cutting experiments. Therefore, L-UVAM can be applied in efficient machining of SiC p /Al composites. [ABSTRACT FROM AUTHOR]

A three-dimensional model of heating an anisotropic sample by laser radiation is presented. The influence of an oblique incidence of the beam and different orientations of the material structure relative to the Cartesian coordinate system is studied. It is shown that in the case of Ti-6Al-4V sintered powder, an inclusion of these phenomena into consideration has a significant effect on the maximum heating temperature and heating depth. [ABSTRACT FROM AUTHOR]

As device length scales trend downward, small feature sizes and steep temperature gradients require thermometers with increasingly fine spatial resolution in order to capture the true peak temperature. Here, we develop analytical expressions for the true and measured temperature rises as a function of thermometer size for Gaussian, disk-shaped, and rectangular surface heat sources. We find that even a thermometer the same size as the hotspot can underestimate the true peak temperature rise by more than 15%, and this error frequently exceeds 75% and can approach 90% for certain geometries when the thermometer is ten times larger than the measured hotspot. We show that a thermometer with resolution approximately two times smaller than the hotspot size is required to measure the peak temperature rise with less than 5% error for several common hotspot geometries. We also experimentally demonstrate that a 50 × 50 × 50 nm3 individual upconverting NaYF4:Yb3+,Er3+ nanoparticle thermometer captures the peak temperature rise due to laser heating more accurately than conventional diffraction limited optical techniques that our modeling results show would underestimate this value. In contrast to apparent self-heating effects that spuriously increase the nanoparticle thermometry signal at high excitation intensities, we measure true laser heating, as confirmed by comparing measurements on glass and diamond substrates. [ABSTRACT FROM AUTHOR]

A simple kHz-rate spectral phosphor thermometry technique with sub-millisecond temporal resolution for contactless point measurements of short duration transient surface temperature changes was developed by employing a compact high-speed fiber-optic spectrometer, a high repetition rate pulsed green laser, and a fast decaying thermographic phosphor. Temperature changes were determined from the temperature-dependent emission spectra of the YAG:Ce phosphor using a spectral slope method. The precision of single-shot temperature measurements was better than 4% for temperatures up to 700 K. An application of the technique for time-resolved measurements of local transient temperature changes at 5 kHz during repetitive long CO2 laser pulse heating is presented. The measured temperature transients are well-predicted using a two-dimensional axisymmetric heat transfer model. [ABSTRACT FROM AUTHOR]

We have developed nano/microscale thermal impulse (TI) (i.e., temperature and duration) sensors for use in extreme environments such as explosions, furnaces, and combustion experiments. These sensors consist of chemically bonded precursor Eu : ZrO 2 and precursor Dy : Y 2 O 3 , which are prepared via mixed coprecipitation. In this study, we demonstrate their functionality for subsecond pulsed laser heating (isothermal duration of ≈ 10 ms) up to 1773 K, with evidence suggesting functionality to even higher temperatures. This large range is due to the formation of a new mixed-material phase (similar to yttria-stabilized zirconia) that results in spectral features that are not seen in the component materials on their own. To the best of our knowledge, this material has the largest functional temperature range of any ex situ TI sensor reported in the literature. [ABSTRACT FROM AUTHOR]

Pentazolate compounds have attracted extensive attention as high energy density materials. The synthesis and recovery of pentazolate compounds is of great importance for their potential applications. Here, we report the synthesis of Pmn 21-NaN5 and Pm -Na2N5 through compressing and laser heating pure NaN3 at ∼ 60 GPa. Upon decompression, the pressure-induced structural transition from Pmn 21-NaN5 into Cm -NaN5 is observed in the pressure range of 14–23 GPa for the first time. The cyclo- N 5 − can be traced down to 4.7 GPa at room temperature and recovered to ambient pressure under low temperature condition (up to 160 K). The Pm -Na2N5 is suggested to decompose into the P 4/ mmm -NaN2 at 23 GPa, and be stable at ambient conditions. This work provides insight into the high-pressure behaviors of pentazolate compounds and an alternative way to stabilize energetic polynitrogen compounds. [ABSTRACT FROM AUTHOR]

In this study, we propose a new sub-diffusion two-temperature model and its accurate numerical method by introducing the Knudsen number ( K n ) and two Caputo fractional derivatives ( 0 < α , β < 1 ) in time into the parabolic two-temperature model of the diffusive type. We prove that the obtained sub-diffusion two-temperature model is well posed. The numerical scheme is obtained based on the L 1 approximation for the Caputo fractional derivatives and the second-order finite difference for the spatial derivatives. Using the discrete energy method, we prove the numerical scheme to be unconditionally stable and convergent with O (τ min { 2 − α , 2 − β } + h 2) , where τ , h are time and space steps, respectively. The accuracy and applicability of the present numerical scheme are tested in two examples. Results show that the numerical solutions are accurate, and the present model and its numerical scheme could be used as a tool by changing the values of the Knudsen number and fractional-order derivatives as well as the parameter in the boundary condition for analyzing the heat conduction in porous media, such as porous thin metal films exposed to ultrashort-pulsed lasers, where the energy transports in phonons and electrons may be ultraslow at different rates. [ABSTRACT FROM AUTHOR]

In this study, the effects of laser light on the heat transfer of a thin beam heated by an applied current and voltage are investigated. Laser heating pulses are simulated as endogenous heat sources with discrete temporal properties. The heat conduction equation is developed using the energy conservation equation and the modified Moore–Gibson–Thompson (MGT) heat flow vector. Thermal and structural analysis of Euler–Bernoulli microbeams is provided with the support of visco-Pasternak's base with three parameters. Using the Laplace transform method, an approximation of an analytical solution is found for the field variables being examined. A comparison was made of the impacts of laser pulse length, the three foundation coefficients, and the thermal parameters on the responses to changes in measured thermophysical fields, such as deflection and temperature. [ABSTRACT FROM AUTHOR]

The dielectric metasurface has become a powerful tool for compact optical components with various wavefront controlling functionalities accompanied by negligible losses at the corresponding working frequencies. In this work, we propose a tunable all-dielectric metasurface as an optical filter with high resolution covering different optical communication bands, where tunability is realized by a combination of changing the incident angle and modulating the refractive index of an optical phase changing material (OPCM). When the incident angle varies, our optical filter based on a two-dimensional bound state in continuums (BIC) metasurface can achieve sequential, extremely sharp resonances. In addition, the resonance peaks could be further shifted to a different frequency band by the refractive index change of OPCM via pulsed laser heating. The proposed scheme can offer optical filters with high spectral resolution and large tunable working wavelength range, which greatly benefits from the topological property of BIC and large modulation depth of OPCM. [ABSTRACT FROM AUTHOR]

In this work, laser heating is used to experimentally investigate the high-temperature behavior of the U-Fe-Zr-O system using arc-melted samples with various nominal compositions. Three-phase transitions are observed in the vicinity of ~1100, ~1700, and ~2200 K. Principal component analysis of the phase transition temperatures in the course of laser-heating thermal cycling indicates that the phase transition around ~1100 K is driven by the interaction of stainless steel (SS) with metallic U, the phase transition around ~1700 K by the melting of stainless steel, and the phase transition above ~2000 K by the eutectic melting of UO2. The results also reveal two hitherto overlooked interactions in the U-Fe-Zr-O system, which could have severe consequences for the containment of corium inside the reactor pressure vessel (RPV). First, the phase transition temperatures of the samples varied extensively as a result of the laser-driven rapid thermal cycling. Variations of up to 390 K were observed in the phase transition temperatures, suggesting that depending on the initial conditions of corium formation, the corium-driven ablation of the RPV wall could commence significantly earlier than the current state-of-the-art severe accident codes would predict. Additionally, evidence of a large exothermic reaction between zirconium and molten steel was observed upon SS melting. Such phenomenon may also be driven by material segregation during fast heating and cooling. If such a mechanism is activated during a severe nuclear accident, it can have an important impact on the overall thermal balance of the RPV. [ABSTRACT FROM AUTHOR]