Threshold Laser Energy Research Articles

Reversible Single‐Pulse Laser‐Induced Phase Change of Sb2S3 Thin Films: Multi‐Physics Modeling and Experimental Demonstrations

AbstractPhase change materials (PCMs) have gained a tremendous interest as a means to actively tune nanophotonic devices through the large optical modulation produced by their amorphous to crystalline reversible transition. Recently, materials such as Sb2S3 emerged as particularly promising low loss PCMs, with both large refractive index modulations and transparency in the visible and near‐infrared. Controlling the local and reversible phase transition in this material is of major importance for future applications, and an appealing method to do so is to exploit pulsed lasers. Yet, the physics and limits involved in the optical switching of Sb2S3 are not yet well understood. Here, the reversible laser‐induced phase transition of Sb2S3 is investigated, focusing specifically on the mechanisms that drive the optically induced amorphization, with multi‐physics considerations including the optical and thermal properties of the PCM and its environment. The laser energy threshold for reversibly changing the phase of the PCM is determined through both theoretical analysis and experimental investigation, not only between fully amorphous and crystalline states but also between partially recrystallized states. Then, the non‐negligible impact of the material's polycrystallinity and anisotropy on the power thresholds for optical switching is revealed. Finally, the challenges related to laser amorphization of thick Sb2S3 layers are addressed, as well as strategies to overcome them. These results enable a qualitative and quantitative understanding of the physics behind the optically‐induced reversible change of phase in Sb2S3 layers.

Laser‐Induced Nucleation of Acetaminophen through the Addition of Insoluble Impurities and Acidic Polymers

AbstractThis study investigates the crystallization of acetaminophen (ACET) in ultrapure water and a 10 wt.% aqueous polyacrylic acid (PAA) solution using non‐photochemical laser‐induced nucleation (NPLIN) for the first time. Using a 532 nm nanosecond laser, two distinct crystal morphologies—rhombic and tetragonal plate‐like—are formed in both solvents after adding impurities. Notably, the PAA solution showed a reduced number of crystals and slower growth rates compared to ultrapure water, suggesting that the acidic polymer modulates crystal growth. Interestingly, crystals are not induced by the laser without impurities. However, impurities like copper phthalocyanine (CuPc) or boron carbide (CB4) enabled successful NPLIN, with CB4 showing higher nucleation efficiency than CuPc. The study also explores how laser power affects nucleation probability and identifies potential laser energy thresholds. Experimental data on ACET crystal sizes over time are fitted to derived equations, which accurately represented trends and predicted results. The nanoparticle heating mechanism and the role of acidic polymers in affecting nucleation probability and growth rate are discussed, along with potential mechanisms for changes in crystal morphology.

Comparative study of the multiple wavelength lasing of nitrogen ions: the role of vibrational level-dependent photoionization

We report on an optical amplification and energy threshold of the two most prominent emission lines, 391.4 and 427.8 nm, of the cavity-less lasing of nitrogen ions pumped by femtosecond laser pulses. It was found that the two transitions both show optical amplification under a low gas pressure condition, while the 391.4 nm emission is barely amplified under high gas pressure. Moreover, the 427.8 nm emission presents a significant lower pump laser energy threshold and a larger gain factor than the 391.4 nm emission. Numerical simulations based on a three-state coupling model suggest that the smaller ionization Franck–Condon factor from the ground state of N2 to the vibrational level ν = 1 in X2Σ g + state of N2+ favors the formation of population inversion corresponding to the 427.8 nm emission. Meanwhile, the competition between the strong field ionization and excitation induced by the pumping laser requires higher laser intensity to acquire the population inversion for the 391.4 nm radiation, leading to a corresponding larger energy threshold.

Advancing carbohydrate quantification in MALDI mass spectrometry by the rapidly freeze-drying droplet (RFDD) method.

Quantitative carbohydrate analysis faces challenges in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), including insufficient sensitivity and inconsistent spatial distribution of ion intensity. This study introduces an innovative sample preparation approach, the Rapidly Freeze-Drying Droplet (RFDD) method, aimed at overcoming these challenges by enhancing the homogeneity of the sample morphology and signal intensity in MALDI. Compared to conventional preparation methods, the RFDD method reduces the laser energy threshold and demonstrates a remarkable increase in signal intensity for carbohydrates, facilitating the detection of high-molecular-weight polysaccharides (>10 kDa). The RFDD-prepared samples exhibit a uniformly distributed signal intensity that overcomes the 'sweet spot' issue in MALDI. The enhanced signal intensity and reproducibility lead to reliable quantitative analysis of carbohydrates, eliminating the need for expensive isotopic standards in each sample. A straightforward and accessible approach is presented for general laboratories, revolutionizing carbohydrate analysis in MALDI-MS.

Experimental investigation of various energy-absorbing layer materials and sodium alginate viscosities on the jet formation in laser-induced-forward-transfer (LIFT) bioprinting

Laser-induced-forward-transfer (LIFT) bioprinting technology has been viewed as a regenerative medicine technology because of its high printing quality and good cell viability. To stabilize the jet to achieve high-quality printing, an energy-absorbing layer (EAL) can be introduced. In this study, three materials (graphene, gelatin, and gold) were utilized as the EAL. The effect of each EAL on the jet generation process was investigated. Besides, the effect of graphene EAL thickness was addressed for various experimental conditions. The jet generation process using sodium alginate solutions with different concentrations (1 and 2 wt. %) was also discussed to investigate the effect of viscosity. The time sequence images of the formed jets utilizing three EALs showed that both graphene EAL and gelatin EAL can promote the formation of jet flow. For the gold EAL, no jet flow was observed. This study provides experimental verifications that the interaction between laser and EAL materials can result in different jets due to various dominant interaction mechanisms. For example, strong absorption in the infrared range for the graphene EAL, strong scattering loss for the gelatin EAL, and strong absorption in the ultraviolet range but weak absorption in the infrared for the gold EAL. We also observed the holes left on the EAL after the printing was completed. The thermal effect is dominant to create regular and round shape holes for the graphene EAL, but it changes to the mechanical effect for the gold EAL because of the existence of irregular and unorganized holes. In addition, we identified the existence of an input laser energy threshold value for a certain thickness graphene EAL. More laser energy is required to break down thicker graphene EALs, which will result in a higher initial jet velocity. Furthermore, we explored the effect of sodium alginate (SA) solution's viscosity on the generated jet. We found that a high-viscosity SA solution can result in a low initial jet velocity, a short jet, and small droplets on the receiving substrate. The findings from this study help determine the mechanisms of EAL–laser interaction with different EAL materials in the LIFT process. This work aims to facilitate the development of new EAL and bioink to achieve stable jet formation and high printing quality in future LIFT bioprinting.

Mechanisms responsible for the onset of selective laser flash sintering of 8‐YSZ

AbstractSelective laser flash sintering (SLFS) is a variation of flash sintering where the only external heat source is a scanning laser. The scanning laser locally heats a region of the sample between two electrodes, initiating measured current flow at a threshold electric field and laser energy density. This study focuses on understanding how charge transport occurs during stage I SLFS in 8 mol% yttria stabilized zirconia. Two potential charge transport mechanisms are considered: (1) a continuous current moving along a hot line between electrodes and (2) charge transported in a discrete bundle within a hot spot, localized to the area under the laser beam. Two laser scan patterns are employed to experimentally determine how charge is transported during stage I SLFS. Numerical modeling is used to estimate the temperatures at which SLFS initiates, which allows the calculation of charge carrier densities and mobilities relevant for the onset of SLFS. Results demonstrate that both a discrete bundle of charges and continuous flow of charge carriers contribute to the current at the onset of SLFS.

Influence of Asymmetric Agglomerations Effects over the Photothermal Release of Liposome-Encapsulated Nanodiamonds Assisted by Opto-Mechanical Changes

An analysis of optical effects exhibited by blood plasma under healthy/unhealthy conditions, and of the penetrating evolution of nanovehicles conformed by nanodiamonds (NDs) encapsulating liposomes (L) within these biofluids, is presented. Optical ablation of liposome clusters was actuated and controlled by a standard two-wave mixing (λ = 532 nm, τp = 4 ns) laser light method. Radiant time exposure effects (30 min) and threshold laser energy parameters (250 mJ/cm2 numerical; 181 mJ/cm2 experimental) necessary to release NDs were identified and confirmed with similar experiments in the literature. Interactions during the sedimentation process between nanovehicles and the laser beams barrier were considered as the principal thermal damage process to achieve the release and transportation of drugs within these static fluids. The mechanical response during the release of NDs focuses on the temperature propagation, dynamic effects of nanovehicles associated with the diffusion coefficient, and some agglomeration effects. The principal findings of this research concern the threshold temperature (51.85 °C) of liposomes for the release of NDs with respect to that typically quoted in the literature (40–70 °C) for pure liposomes. The assessment of the release of NDs focuses on the numerical magnitude of Quantum Yield. Furthermore, the optical contrast enhancement was associated with NDs size agglomerations and the healthy/unhealthy conditions of fluids. This research aims to be a first proof approximation for delivery and transportation approaches to guide and interpret outcomes when combined with the vectorial nature basis of laser light and further effects once the cargo is retained in the fluids.

Thermal-induced effects on ultrafast laser filamentation in ethanol

Fs laser filamentation in ethanol is studied for bottom-up nanomaterials synthesis at different laser repetition rate. Measurements of energy loss, visible conical images, transmitted beam profile and the optical emission spectra show that laser repetition rate affects ultrafast laser filamentation in ethanol significantly because of the induced thermal processes. Firstly, near the threshold laser energy for self-focusing, high laser repetition rate could interfere with the process, via thermal defocusing that inhibits the onset of filamentation. An enlarged, near flat-top laser beam is produced for the conditions that favor thermal lensing. Secondly, at high laser energy, thermal defocusing effect is saturated as convective heat dissipation occurs. Thus, self-focusing prevailed and led to filamentation at all repetition rates. The strong convection at high laser repetition rate increases the rate of reactions for nanodiamonds synthesis, as the flow of fresh ethanol precursor to the localized filamentation zone is enhanced.

Displacement damage and single event effects of SiC diodes and MOSFETs by neutron, heavy ions and pulsed laser

SiC diodes and MOSFETs (device under test, DUTs) have been tested by neutron and heavy ions, pulsed laser separately or both. Neutron displacement damage (DD) results show that up to 1E12/cm2 neutrons there is no significant leakage current increasing; DUTs have been tested by heavy ion and pulsed laser to get their single event burnt-out (SEB) threshold at some working voltages, results show that pulsed laser and heavy ion are consistent with each other. Then one of the diodes and MOSFETs which has been tested by neutron was tested by pulsed laser to get SEB laser energy threshold, results show after neutron test SEB threshold laser energies will decrease obviously, with laser energy equivalence linear energy transfer (ELET) decrease much more. All the results mentioned above show that DD will distinctly affect SEB capabilities of SiC chips, DD will induce a leakage current path, which will decrease SEB threshold LET when SEE will also cause a leakage current path.

Core‐Shell Hetero‐Framework derived Copper Azide Composites as Excellent Laser‐Ignitable Primary Explosives

AbstractLaser initiation has attracted increasing interest owing to its extraordinary safety and high reliability. However, traditional metal complex‐based laser‐ignitable primary explosives are limited by high input laser energy and low detonation ability. In this study, an efficient laser‐ignitable primary explosive‐based copper azide is prepared by constructing core‐shell hetero‐framework Cu‐MOF@COF as the precursor. The pyrolysis of Cu‐MOF@COF hybrid material affords copper azide (CA) nanoparticle confined in a porous carbon shell, referred to CA@C Shell. The evenly coated porous carbon shell functions as light‐to‐heat conversion layer efficiently promoting the laser initiation process of inside CA. Consequently, CA@C Shell can be initiated at lower laser energy thresholds (0.80 mJ at 1064 nm). This value is significantly lower than typical laser ignitable metal complex tetraamine‐cis‐bis(5‐nitro‐2H‐tetrazolato‐N2)cobalt(III)perchlorate (726 mJ at 808 nm). Moreover, the CA@C Shell successfully detonates the secondary explosives CL‐20 by laser energy when it is assembled in a micro‐detonator system. This study offers a unique method for constructing high performance laser‐ignitable primary explosives for micro‐detonator applications.

Laser-Induced Plasmonic Nanobubbles and Microbubbles in Gold Nanorod Colloidal Solution.

In this work, we studied the initiated plasmonic nanobubbles and the follow-up microbubble in gold nanorod (GNR) colloidal solution induced by a pulsed laser. Owing to the surface plasmon resonance (SPR)-enhanced photothermal effect of GNR, several nanobubbles are initiated at the beginning of illumination and then to trigger the optical breakdown of water at the focal spot of a laser beam. Consequently, microbubble generation is facilitated; the threshold of pulsed laser energy is significantly reduced for the generation of microbubbles in water with the aid of GNRs. We used a probing He-Ne laser with a photodetector and an ultrasonic transducer to measure and investigate the dynamic formations of nanobubbles and the follow-up microbubble in GNR colloids. Two wavelengths (700 nm and 980 nm) of pulsed laser beams are used to irradiate two kinds of dilute GNR colloids with different longitudinal SPRs (718 nm and 966 nm). By characterizing the optical and photoacoustic signals, three types of microbubbles are identified: a single microbubble, a coalesced microbubble of multiple microbubbles, and a splitting microbubble. The former is caused by a single breakdown, whereas the latter two are caused by discrete and series-connected multiple breakdowns, respectively. We found that the thresholds of pulsed energy to induce different types of microbubbles are reduced as the concentration of GNRs increases, particularly when the wavelength of the laser is in the near-infrared (NIR) region and close to the SPR of GNRs. This advantage of a dilute GNR colloid facilitating the laser-induced microbubble in the NIR range of the bio-optical window could make biomedical applications available. Our study may provide an insight into the relationship between plasmonic nanobubbles and the triggered microbubbles.

Rapid Selective Ablation and High-Precision Patterning for Micro-Thermoelectric Devices Using Femtosecond Laser Directing Writing.

Highly integrated miniature thermoelectric (TE) devices are desirable for applications of chip thermal management and self-powered energy harvesting. Currently, further performance improvement of micro-TE devices is largely limited by micro-nano-patterned processing, which shows the incompatibility with high-performance TE material fabrication or contradiction between machining accuracy and efficiency. This work presents a useful method to flexibly achieve high-precision array patterning for the micro-TE device through the femtosecond laser direct writing technique. By experimentally examining the material ablation process and numerically analyzing the electron-lattice temperature, the laser energy threshold for different materials is determined to obtain the selective removal between TE materials and metallic electrodes. Furthermore, the evaluation criteria are established between the formation quality of microgroove in the array structure and the laser pulse energy distribution, and the shape-control and property-control pattern processing can be realized through the reasonable control of the laser energy. Consequently, the Bi2Te3-based TE pattern with a competitive leg density (496 pairs/cm2) and a high filling factor (55%) is successfully constructed.

Research on Single Event Burnout of GaN power devices with femtosecond pulsed laser

The femtosecond pulsed laser is used to study the quantitative evaluation technology of the single event burnout (SEB) effect in GaN power devices. In this work, we establish two pulsed-laser effective energy transmission models for different device structures, analyzing and verifying the equivalent relationship between the effective laser energy and the heavy ion linear energy transmission (LET). The critical parameters of models are confirmed, including laser parameters and device parameters. The interface reflectivity between the layers is mainly considered. Meanwhile, the parameters are corrected by the multiple reflections between the interfaces, and the laser energy of the second reflection of the metal layer is considered. These measures can be used to reduce the error of the effective energy in the device active area. In addition, we validate the models experimentally. A gallium nitride high electron mobility transistor (GaN HEMT) and a schottky barrier diode (SBD) power device are used in the experiment on the irradiation by a femtosecond pulse laser. The effective laser energy thresholds and the laser equivalent LET threshold with two incident wavelengths of the SEB are calculated. The theoretical calculation value and the actual measured value are compared. The selcction basis of the laser wavelengths is given by the detailed study. The support for the laser quantitative evaluation and the protection design of the SEB in GaN power devices is provided by this work.

Nanosecond laser shock detonation of nanodiamonds: from laser-matter interaction to graphite-to-diamond phase transition

Nanodiamonds (NDs) have been widely explored for applications in drug delivery, optical bioimaging, sensors, quantum computing, and others. Room-temperature nanomanufacturing of NDs in open air using confined laser shock detonation (CLSD) emerges as a novel manufacturing strategy for ND fabrication. However, the fundamental process mechanism remains unclear. This work investigates the underlying mechanisms responsible for nanomanufacturing of NDs during CLSD with a focus on the laser-matter interaction, the role of the confining effect, and the graphite-to-diamond transition. Specifically, a first-principles model is integrated with a molecular dynamics simulation to describe the laser-induced thermo-hydrodynamic phenomena and the graphite-to-diamond phase transition during CLSD. The simulation results elucidate the confining effect in determining the material’s responses to laser irradiation in terms of the temporal and spatial evolutions of temperature, pressure, electron number density, and particle velocity. The integrated model demonstrates the capability of predicting the laser energy threshold for ND synthesis and the efficiency of ND nucleation under varying processing parameters. This research will provide significant insights into CLSD and advance this nanomanufacturing strategy for the fabrication of NDs and other high-temperature-high-pressure synthesized nanomaterials towards extensive applications.

Numerical and experimental investigation of laser shock microhydroforming technology for microforming thin-walled LA103Z alloy foil with complex microfeatures

In this work, laser shock microhydroforming technology was further investigated. This technology employs liquid as the laser-induced shock wave transmission medium to microform a thin-walled LA103Z magnesium–lithium (Mg-Li) alloy foil with six bump features. A finite element model established by Hypermesh/LS-DYNA was used to illustrate the dynamic transmission of the liquid shock wave and the dynamic plastic deformation of the workpiece. The mechanism by which the liquid shock wave interacted with the closed liquid chamber to generate a homogenised shock wavefront was revealed. The dynamic loading form of the liquid shock wave and the characteristics of the microfeatures of the workpiece resulting from this dynamic loading form were also analysed mechanically. A comparison of the effects of liquid type and laser energy in this process showed that using castor oil as the liquid medium at threshold laser energy achieved the best plastic forming effect of the workpiece. Analysis of the thickness distribution of the workpiece revealed that the rupture was concentrated in the shear thinning region at the edge of the bump features caused by the transient large stress when the laser energy exceeded the threshold value.

Diode-pumped all-fiber-optic liquid dye laser

We report the experimental results of a fiber-based Fabry–Perot cavity dye laser structure. The structure is transversely pumped by a pulsed blue laser diode through an optical fiber. The active medium used consists of the dye fluorescein sodium dissolved in glycerine. A lasing around 580 nm has been observed when the laser threshold energy of about 46 nJ pulse−1 is reached. The results will contribute to the creation of a fully integrated diode-pumped all-fiber-optic dye laser source.

Simulation of impulsively induced viscoelastic jets using the Oldroyd-B model

Abstract

Phase Transition Photodetection in Charge Density Wave Tantalum Disulfide.

The charge density wave (CDW) phase is a macroscopic quantum state with periodic charge density modulation accompanied by periodic lattice distortion in low-dimensional metals. External fields, such as an electric field and optical excitation, can trigger the transitions among different CDW states, leaving an under-explored mechanism and attracting great interest toward optoelectronic applications. Here, we explore a photoinduced phase transition in 1T-TaS2 under an electrical field. By analyzing the phase transition probability, we obtained a linear dependence of the phase transition barrier on the electric field and laser energy density. Additionally, the threshold laser energy for the phase transition decreases linearly with an increasing applied electrical field. Finally, picojoule photodetection was realized in the visible and near-infrared ranges near the CDW transition edge. Our work will promote the understanding of the CDW phase transition mechanism as well as open pathways for optoelectronic applications.

Application of Two-Photon-Absorption Pulsed Laser for Single-Event-Effects Sensitivity Mapping Technology.

Single-event effects (SEEs) in integrated circuits and devices can be studied by utilizing ultra-fast pulsed laser system through Two Photon Absorption process. This paper presents technical ways to characterize key factors for laser based SEEs mapping testing system: output power from laser source, spot size focused by objective lens, opening window of Pockels cell, and calibration of injected laser energy. The laser based SEEs mapping testing system can work in a stable and controllable status by applying these methods. Furthermore, a sensitivity map of a Static Random Access Memory (SRAM) cell with a 65 nm technique node was created through the established laser system. The sensitivity map of the SRAM cell was compared to a map generated by a commercial simulation tool (TFIT), and the two matched well. In addition, experiments in this paper also provided energy distribution profile along Z axis that is the direction of the pulsed laser injection and threshold energy for different SRAM structures.

Prediction of the spatial location of a laser-induced breakdown in argon

A modelling of the laser-induced breakdown spatial location is presented and compared to experiments where the considered variables are the incident laser energy and the initial pressure of argon in the vessel. The proposed modelling is based on the assumption that the conservation of the threshold laser energy per unit surface needs to produce a breakdown. The experiment consists in 100 consecutive laser shots for eight laser energies from 4.48 to 147.81 mJ at λ = 532 nm and four initial pressures, from 0.25 to 1 bar. A dimensionless number, E/Eth, is also proposed to compare all obtained data to each other with E the incident energy and Eth the threshold energy below the one no breakdown appears. The proposed modelling is in good agreement with observed values (<10% in most experiments) and is particularly interesting for laser-induced breakdown spectroscopy in gas where the location of the plasma is of great importance.