Threshold Energy Density Research Articles

Theoretical analysis and experimental verification of scintillator luminescence nonlinearity based on carrier quenching model

<sec>The scintillator detector is one of the most important detectors in the field of radiation detection and radiation physics. The characteristics and performance of scintillator that is a core part of the measurement system, are widely studied. Especially, the nonlinearity of scintillators under high excitation density has received more attention because of its direct influence on the measurement results. In this paper, physical modeling and experimental research on this problem are carried out in-depth.</sec><sec>First, the second-order quenching effect of excitons on the scintillator luminescence process is quantitatively analyzed based on the carrier dynamic equation. The luminescence attenuation curves of scintillator under different initial carrier concentrations generated by different excitation densities are obtained. The relationship of the light yield and the efficiency of scintillator with the initial carrier concentration is analyzed, and the results show that with the increase of the initial carrier concentration, the light yield tends to be saturated and the light efficiency decreases. Then CeF<sub>3</sub> scintillator is studied in the Z-scan photoluminescence experiment. The relationship between the light yield and the excitation density is obtained, and the experimental data can be fitted by the carrier quenching model well, which verifies the physical model. At the same time, the energy density threshold corresponding to the 10% nonlinearity of CeF<sub>3</sub> scintillator is obtained.The physical model established in this paper can be used to predict and explain the nonlinear luminescence of various scintillation materials according to different parameters of crystal materials, which is important to understand and solve the nonlinearity problem of scintillators under high excitation density in practical application of radiation detection.</sec>

Compaction Quality Fine Control of Fresh Concrete Based on Vibration Energy

To solve the problem of difficulty in controlling the construction quality of fresh concrete due to the low applicability and accuracy for the existed referencing vibration time when using internal vibrator, an innovative parameter of vibration energy density is created based on concept of energy and a hardened porosity prediction model is constructed considering the parameter and mix characteristics. The model is used to obtain the minimum porosity value of concrete and corresponding energy density threshold under certain ratio conditions. Finally, the accuracy and effectiveness of method are verified by field tests. The results show the method can realize precise quantitative quality control of concrete vibration and guide the construction work.

Transmission electron microscopy study of extended defect evolution and amorphization in SiC under Si ion irradiation

ABSTRACTThe damage induced in 3C‐SiC epilayers on a silicon wafer by 2.3‐MeV Si ion irradiation for fluences of 1014, 1015, and 1016 cm−2, was studied by conventional and high‐resolution transmission electron microscopy (TEM/HRTEM). The evolution of extended defects and lattice disorder is followed in both the 3C‐SiC film and Si substrate as a function of ion fluence, with reference to previous FTIR spectroscopy data. The likelihood of athermal unfaulting of native stacking faults by point defect migration to the native stacking faults is discussed in relation to damage recovery. Threshold energy densities and irradiation doses for dislocation loop formation and amorphous phase transformation are deduced from the damage depth profile by nuclear collisions. The role of electronic excitations on the damage recovery at high fluence is also addressed for both SiC and Si.

Surface integrity control of laser cleaning of an aluminum alloy surface paint layer.

Removal of a paint layer of 2024 aluminum alloy was studied using a nanosecond fiber pulsed laser with a maximum power of 30 W and the influence of laser cleaning energy density on the surface integrity of the substrate was explored. The cleaning energy density threshold of the paint layer is 17.69J/cm2 and the damage energy density threshold is 24.77J/cm2. The optimum cleanliness and surface integrity of laser cleaning were obtained when the energy density was 21.23J/cm2. Microhardness and Young's modulus of the surface after laser cleaning were improved by 6% and 25%, respectively. The mechanical properties of the surface of the substrate after laser cleaning were significantly improved, which is an advantage for this high-quality non-destructive cleaning technology of the aircraft skin surface paint layer.

Impact of nanosecond laser energy density on the C40-TiSi2 formation and C54-TiSi2 transformation temperature

The formation of Ti based contacts in new image sensor complementary metal–oxide–semiconductor technologies is limited by the requirement of a low thermal budget. The objectives of these new 3D-technologies are to promote ohmic, low resistance, repeatable, and reliable contacts by keeping the process temperature as low as possible. In this work, ultraviolet-nanosecond laser annealing was performed before classical rapid thermal annealing (RTA) to promote the formation at lower RTA temperatures of the low resistivity C54-TiSi2 phase. The laser energy density was varied from 0.30 to 1.00 J/cm² with three pulses in order to form the C40-TiSi2 phase and finally to obtain the C54-TiSi2 phase by a subsequent RTA at low temperatures. The formed Ti-silicides were characterized by four-point probe measurements, x-ray diffraction, transmission electron microscopy, and atom probe tomography. A threshold in the laser energy density for the formation of the C40-TiSi2 is observed at an energy density of 0.85 J/cm² for the targeted TiN/Ti stack on blanket wafers. The C40-TiSi2 formation by laser annealing prior to RTA enables to reduce the formation temperature of the C54-TiSi2 phase by 150 °C in comparison to a single RTA applied after the Ti/TiN deposition. This specific phase sequence is only observed for a laser energy density close to 0.85 J/cm². At higher energy densities, the presence of C49-TiSi2 or a mixture of C49-TiSi2 and C54-TiSi2 is observed. The underlying mechanisms of the phase sequence and formation are discussed in detail.

Influence of Laser Powder Bed Fusion Process Parameters on Voids, Cracks, and Microhardness of Nickel-Based Superalloy Alloy 247LC.

The manufacturing of parts from nickel-based superalloy Alloy 247LC by laser powder bed fusion (L-PBF) is challenging, primarily owing to the alloy’s susceptibility to cracks. Apart from the cracks, voids created during the L-PBF process should also be minimized to produce dense parts. In this study, samples of Alloy 247LC were manufactured by L-PBF, several of which could be produced with voids and crack density close to zero. A statistical design of experiments was used to evaluate the influence of the process parameters, namely laser power, scanning speed, and hatch distance (inherent to the volumetric energy density) on void formation, crack density, and microhardness of the samples. The window of process parameters, in which minimum voids and/or cracks were present, was predicted. It was shown that the void content increased steeply at a volumetric energy density threshold below 81 . The crack density, on the other hand, increased steeply at a volumetric energy density threshold above 163 . The microhardness displayed a relatively low value in three samples which displayed the lowest volumetric energy density and highest void content. It was also observed that two samples, which displayed the highest volumetric energy density and crack density, demonstrated a relatively high microhardness; which could be a vital evidence in future investigations to determine the fundamental mechanism of cracking. The laser power was concluded to be the strongest and statistically most significant process parameter that influenced void formation and microhardness. The interaction of laser power and hatch distance was the strongest and most significant factor that influenced the crack density.

Multilevel reversible laser-induced phase transitions in GeTe thin films

This paper presents the results of a study on the structural properties and dynamics of conductivity of thin (d ∼ 100 nm) films of germanium telluride depending on the phase states reversibly switched by nanosecond pulsed laser radiation with a «top hat» beam profile. It was determined that the threshold of laser radiation energy density at which the phase transition in GeTe thin films from the amorphous to crystalline state is in the range of E = 7.5 ÷ 47.6 mJ/cm2, and the threshold for the reverse transition from the crystalline to amorphous state starts from 47.6 mJ/cm2 and is observed up to 90 mJ/cm2 with no visible damage caused by the ablation. The full time of conductivity change associated with the phase transition between the amorphous and crystalline phases is τCA = 20.2 ns, while for the reverse crystalline to amorphous transition, the conductivity full change time it makes τAC = 52 ns.

Sialolithiasis: Application parameters for an optimal laser therapy.

In-vitro experimental parametric studies of laser ablation using natural sialoliths and artificial stones have been performed toward an efficient laser treatment of sialolithiasis. Surface microstructure and water adsorption become critical for coupling high power pulsed Ho:YAG laser radiation (λ = 2080 nm, τ ∼250 μsec), inducing ablative interactions and stone fragmentation. Results reveal a generic trend, with single pulse laser energy density threshold for sialolith ablative erosion at ∼200 J cm-2 (corresponding to intensity ∼800 kW cm-2 ) and fragmentation rates reaching ∼1 mm/pulse at ∼2400 J cm-2 . This process shows no saturation, suggesting that very high energy density irradiation at low pulse repetition rate is an efficient approach. Such operation facilitates rapid cooling and minimal thermal loading of the oral and maxillofacial area, thus causing negligible adverse effects. The method is expected to contribute to the establishment of an easy and optimal therapeutic protocol for sialolithiasis pathology.

On-Chip Single-Mode Optofluidic Microresonator Dye Laser Sensor

Optofluidic dye laser devices have great potential as coherent light sources for lab-on-a-chip applications such as sensing and spectroscopy applications, owing to their promising properties such as wide wavelength-tunability, proper microfluidic integration, and an extremely miniaturized footprint. The wide emission spectrum of dye molecules and narrow free spectral range of ring resonators, make these lasers inherently multi-mode. In this article, two polydimethylsiloxane-based miniaturized optofluidic ring resonator dye lasers are numerically designed and investigated. First, multi-mode lasing from a single optofluidic ring resonator with a spectral linewidth of 10 nm and a threshold energy density of $2.2~{\mu }\text{j}$ /mm2 is demonstrated. Then, by exploiting two coupled optofluidic ring resonators and Vernier effect, single-mode lasing at a center wavelength of 566 nm with a spectral linewidth as small as ${5.36}\times {10}^{-{4}}$ nm is achieved. Moreover, simulations demonstrate the sensitivity of 500 nm/RIU for the proposed dye laser sensor.

Study of Laser Ablative Destruction of Composites with Nanoscale Coatings of Hafnium and Zirconium Dioxides

An experimental study of laser ablation on the samples that comprise nanofilms of hafnium and zirconium dioxides on the surface of glass and silicon, and obtaining parameters of pulsed laser ablation in this work, provide new data describing the ablation mechanism. The samples were exposed to pulsed radiation from an Nd3+:YAG laser in order to measure the threshold energy density of laser ablation and determine the parameters used in the simulation of statistical distributions. Based on these data, the dependences of the parameters of laser ablation on the optical and thermophysical characteristics of these oxides were obtained.

Time Evolution of Satellite‐Based Optical Properties in Lightning Flashes, and its Impact on GLM Flash Detection

AbstractThe GOES‐16 Geostationary Lightning Mapper (GLM) detection efficiency (DE) is studied over a full year (2018/19) in central Florida using the Kennedy Space Center Lightning Mapping Array (KSC LMA). Mean daily flash DE was 73.8%, and detection was highest during nighttime hours. GLM reported 86.5% of the LMA flashes that had coincident cloud‐to‐ground return strokes reported by the U.S. National Lightning Detection Network. Results also reveal that flash size and duration are critical parameters influencing GLM detection, regardless of the storm type, with 20–40% detection for small and short‐duration flashes and greater than 95% detection for very large and long‐duration flashes.These findings can be explained by examining the time‐evolution of cloud‐top optical emissions observed by the Lightning Imaging Sensor (LIS). Statistical simulations based on long‐term LIS group area observations indicate that about half of the above‐threshold light sources are smaller than a LIS pixel (~ 4 × 4 km) and are smallest during and just after an initial breakdown in IC flashes. This work also demonstrates that for sources smaller than a GLM pixel, the cloud‐top energy detection threshold for GLM is double that for LIS despite GLM's lower energy density threshold. Overall, these findings provide a framework for interpreting GLM performance under varying meteorological conditions, and help explain reports of low flash detection efficiency for storms associated with severe weather, as they typically exhibit high flash rates and resulting small and short‐duration flashes.

Electrochemical evaluation of polyaniline/multi-walled carbon nanotube composite synthesized by microwave plasma polymerization as a supercapacitor electrode

PANI/MWCNT nanocomposite supercapacitor electrodes were synthesized by in-situ microwave plasma polymerization of aniline in the presence of MWCNT-COOH. The SEM image of the composite illustrates the formation of the core-shell MWCNT-PANI ordered structure that has a strong effect on the electrical conductivity and porosity, in addition to the appearance of agglomerated polymerized islands. The electrochemical performance of PANI/MWCNT composite was evaluated with respects to the obtained specific capacitance, energy and power density, and cyclic stability, using cyclic voltammetry, galvanostatic charge/discharge at a constant current and electrochemical impedance spectroscopy. The highest obtained specific capacitance was 112 F/g at a charging current density of 1.6 A/g, provides the highest energy density of 34.8 Wh/Kg and a power density of 1670 W/Kg. While the highest achieved power density was 8381 W/Kg with an energy density of 12.8 Wh/Kg. The delivered energy density crossed the threshold energy density limit of the battery, which meets the scientific motivation to use supercapacitor as an independent energy source.

Characterization, Selection, and Microassembly of Nanowire Laser Systems.

Semiconductor nanowire (NW) lasers are a promising technology for the realization of coherent optical sources with ultrasmall footprint. To fully realize their potential in on-chip photonic systems, scalable methods are required for dealing with large populations of inhomogeneous devices that are typically randomly distributed on host substrates. In this work two complementary, high-throughput techniques are combined: the characterization of nanowire laser populations using automated optical microscopy, and a high-accuracy transfer-printing process with automatic device spatial registration and transfer. Here, a population of NW lasers is characterized, binned by threshold energy density, and subsequently printed in arrays onto a secondary substrate. Statistical analysis of the transferred and control devices shows that the transfer process does not incur measurable laser damage, and the threshold binning can be maintained. Analysis on the threshold and mode spectra of the device populations proves the potential for using NW lasers for integrated systems fabrication.

Experimental Validation of an ITAP Numerical Model and the Effect of Implant Stem Stiffness on Bone Strain Energy

The Intraosseous Transcutaneous Amputation Prosthesis (ITAP) offers transfemoral amputees an ambulatory method potentially reducing soft tissue complications seen with socket and stump devices. This study validated a finite element (in silico) model based on an ITAP design and investigated implant stem stiffness influence on periprosthetic femoral bone strain. Results showed good agreement in the validation of the in silico model against the in vitro results using uniaxial strain gauges and Digital Image Correlation (DIC). Using Strain Energy Density (SED) thresholds as the stimulus for adaptive bone remodelling, the validated model illustrated that: (a) bone apposition increased and resorption decreased with increasing implant stem flexibility in early stance; (b) bone apposition decreased (mean change = − 9.8%) and resorption increased (mean change = 20.3%) from distal to proximal in most stem stiffness models in early stance. By engineering the flow of force through the implant/bone (e.g. by changing material properties) these results demonstrate how periprosthetic bone remodelling, thus aseptic loosening, can be managed. This paper finds that future implant designs should be optimised for bone strain under a variety of relevant loading conditions using finite element models to maximise the chances of clinical success.

Amplified spontaneous emission and optical gain characteristics of sexithiophene single crystals

This paper reports optical properties of a single crystal thiophene/phenylene co-polymer 5,5ʺʺ'-diphenyl-2,2′:5′,2ʺ:5ʺ,2ʺ′:5ʺ′,2ʺʺ:5ʺʺ, 2ʺʺ'-sexithiophene (P6T). The P6T crystals demonstrate high charge carriers’ mobility and large photoluminescence quantum efficiency (PLQE). Herein, the stimulated emission of P6T is studied within wide range of pump energies –refers to energy per pulse – (from 19 ± 0.5 μJ/cm2 to 64.2 ± 0.5 μJ/cm2) through amplified spontaneous emission (ASE) measurements by using Nd-YAG femtoseconds tunable pulsed laser at 445 nm excitation wavelength (λexc). ASE measurements exhibit lower threshold energy density (Eth) i.e., ~26 ± 0.5 μJ/cm2 which confirms optical amplification in P6T at 632 nm emission wavelength. The ASE characteristics of P6T are also studied as a function of different λexc ranging from 425 to 475 nm to find the wavelength for optimum amplification. It is observed that the maximum optical amplification for P6T occurs at a λexc of 445 nm. These crystals exhibit large optical gains which are measured to be 69 cm−1, 53 cm−1 and 29 cm−1 at excitation energies of 91 ± 0.5 μJ/cm2, 66 ± 0.5 μJ/cm2 and 43 ± 0.5 μJ/cm2, respectively. PL measurements of P6T crystals demonstrate large value of the PLQE ~57.36%. This study suggests the potential of P6T single crystal as one of the good candidates among high optical gain materials of its kind for its possible applications in solid-state lasers, photodetectors and optical amplifiers.

Crystal property and spectroscopic investigation on electro-optic and physico-chemical properties of NLO crystal; 3-(3,4-Dihydroxyphenyl)-L-Alanine

In this attempt, in order to obtain high-quality NLO crystal, organic compound; 3-(3,4-Dihydroxyphenyl)-L-Alanine crystal was fabricated. The organic-composite crystal was characterized by crystallographic and spectroscopic tools. The NLO supported parameters like crystal lattice (orthorhombic) and space group (P212121) examined and validated by XRD examination. The SHG test was carried out and SHG efficiency was calculated that1.29 and 1.35 times greater than solid KDP crystal. The laser damage threshold energy density was determined to be 14.51 GW/cm2. By the application of mulliken charge assignment, multiple dielectric cavities were found in crystal material which is able to process the high degree of birefringence gradient. The oscillating chemical potential movement was observed by examining chemical shift, among the core carbons of hexagonal ring and bridge carbons of chain. The chemical softness insists the binding viability of further ligand groups. The π and δ-conjugated interactive complex orbitals recognized on molecular site and participation in optical active mechanism was identified. UV-Visible transmission characteristics of crystal were studied and UV-Visible absorption on degenerate energy states was noted and its band gap energy was estimated. The CT complex of the present case was acknowledged to be COOH group and it causing crystal properties of current organic composite. The hyperactive polarizability was determined as 1775.05 × 10−33 esu and it was found to be five times greater than thiourea. The depletion energy between highly electrophilic zones and protonic zones was estimated to be ±5.241 e 2 causing permanent dielectric characteristics for the title organic composite. The non-superposable on the molecular mirror image was displayed and thereby optical ability was validated.

An energetic approach for the prognosis of thermally induced white etching layers in bearing steel 100CrMn6

Abstract Thermally induced white etching layers (WEL) are known to increase the risk of rolling contact fatigue (RCF) cracks. This study focuses on the potential of an energetic approach for the prognosis of thermally induced WEL in oil-lubricated rolling/sliding contacts. For the determination of power and energy density thresholds a laser surface treatment was selected. The thresholds were determined using non-lubricated flat specimens made of 100CrMn6 bearing steel. The applicability of the energetic approach for the prognosis of WEL appearance in oil-lubricated rolling/sliding contacts was shown using a two-disc test rig. The formation of WEL was achieved by an acceleration process under varying contact parameters such as speed and load. The appearance of WEL was confirmed through metallographic investigations.

Amplified Spontaneous Emission and Optical Gain in Organic Single Crystal Quinquethiophene

In this paper, we report optical characteristics of an organic single crystal oligomer 5,5⁗-diphenyl-2,2′:5′,2″:5″,2‴:5‴,2⁗-quinquethiophene (P5T). P5T crystal is a thiophene/phenylene co-oligomer that possesses better charge mobility as well as photoluminescence quantum efficiency (PLQE) as compared to other organic materials. Stimulated emission in P5T is investigated via amplified spontaneous emission (ASE) measurements within broad pump energies ranging from 35.26 to 163.34 µJ/cm2. An Nd-YAG femtosecond-tunable pulsed laser is used as a pump energy source for the ASE measurements of P5T crystals at an excitation wavelength of 445 nm. The ASE spectra exhibit optical amplification in P5T crystals at a 625 nm peak wavelength with a lower threshold energy density (Eth) ≈ 52.64 μJ/cm2. P5T also demonstrates higher optical gain with a value of 72 cm−1, that is calculated by using the variable stripe-length method. The value of PLQE is measured to be 68.24% for P5T. This study proposes potential applications of P5T single crystals in organic solid state lasers, photodetectors, and optical amplifiers.

Natural Born Laser Dyes: Excited-State Intramolecular Proton Transfer (ESIPT) Emitters and Their Use in Random Lasing Studies.

A series of five excited-state intramolecular proton transfer (ESIPT) emitters based on a 2-(2′-hydroxyphenyl) benzoxazole (HBO) scaffold, functionalized with a mono-or bis-(trialkylsilyl) acetylene extended spacer are presented. Investigation of their photophysical properties in solution and in the solid-state in different matrix, along with ab initio calculations gave useful insights into their optical behavior. Random lasing studies were conducted on a series of PMMA doped thin films, showing the presence of stimulated emission above the threshold of pumping energy density (ρth ≈ 0.5–2.6 mJ cm−2). In this work, the similarity of four level laser systems is discussed in light of the ESIPT photocycle.

Microhardness of Multilayer Composites

When the number of composite layers is increased, the Vickers microhardness and the dependence between the threshold energy density of ablative destruction under the action of a laser pulse related to the average transmittance of light by the composites grow.