Low Laser Research Articles

Influence of strain and point defects on the electronic structure and related properties of (111)NiO epitaxial films

Abstract (111)NiO epitaxial films are grown on c-sapphire substrates at various growth temperatures ranging from room temperature to 600 ∘ C using pulsed laser deposition technique. Two series of samples, where different laser fluences are used to ablate the target, are studied here. Films grown with higher laser fluence, are found to be embedded with Ni-clusters crystallographically aligned with the (111)NiO matrix. While the layers grown with lower laser energy density exhibit p-type conductivity, especially at low growth temperatures. X-ray diffraction study shows the coexistence of biaxial compressive and tensile hydrostatic strains in these samples, which results in an expansion of the lattice primarily along the growth direction. This effective uniaxial expansion ε ⊥ increases with the reduction of the growth temperature. Band gap of these samples is found to decrease linearly with ε ⊥ . This result is validated by density functional theory calculations. Experimental findings and the theoretical study further indicate that V Ni + O I and V O + N i I complexes exist as the dominant native defects in samples grown with Ni-deficient (low laser fluence) and Ni-rich (high laser fluence) conditions, respectively. P-type conductivity observed in the samples grown in Ni-deficient conditions is more likely to result from V Ni + O I defects than Ni-vacancies ( V Ni ).

Structure-Induced Energetic Coordination Compounds as Additives for Laser Initiation Primary Explosives.

Laser ignition of primary explosives presents more reliable alternative to traditional electrical initiation methods. However, the commercial initiator lead azide (LA) requires a high-power density laser to detonate, with the minimum laser initiation energy (Emin) of 2402 mJ. Currently, the laser-ignitable metal complex-based igniters still suffer from weak detonation capabilities and high Emin values. Here, the approach is first proposed to design laser ignition primary explosives within the high energy azide and tetrazole-based energetic coordination compounds (ECCs), [Co(N3)(2-bmttz)(H2O)]2 1 and [Co(N3)(2-bmttz)(MeOH)]2 2 as additives to LA. Material 1e with 4wt.% of 1 in LA, exhibits ultra-low laser initiation threshold (Emin = 1.6 mJ) and ultrafast corresponding time (Tmin = 0.2ms). Specially, compared to LA, the threshold of 1e is as low as 1/1500 of that of LA. Moreover, 30mg 1e successfully detonates RDX with a laser energy of 1.6 mJ. Theoretical calculations and experiment results reveal that 1 exhibits the superior additive effect compared to 2, attributed to its more enhanced ability to generate free radicals and higher photothermal conversion efficiency under laser conditions. This work represents a paradigm shift, with the potential to develop a laser-driven micro-detonator combining powerful detonation capabilities with exceptionally low laser initiation energy.

Design, DFT, experimental, and NLO studies of a new hybrid containing 1,3,4-oxadiazole and indole moieties

Abstract In this article, design and nonlinear optical (NLO) response studies of a new synthesized hybrid molecule (HM 6) containing 1, 3, 4-oxadiazole and indole moieties are introduced. The spatial structure of the target hybrid is analytically determined using 1HNMR, 13CNMR, FT-IR, UV–vis., and Mass spectra. Efficiency of the fully optimized geometry of the synthesized HM (6) is elucidated via energy gap (EHOMO-ELUMO), potential ionization, and electron affinity. The small energy gap leads to efficient NLO response. The cooperation of 1, 3, 4-oxadiazol moiety as a good acceptor and indole as a good donor in the HM (6) enhances long π-conjugation system, led to large hyperpolarizability (β = 2.79 × 10−28 esu). Density functional theory and TD-DFT-assisted calculations proved high potential intramolecular charge transfer and effective β value verify NLO activities. The NLO activities of the HM (6) are examined under the excitation with 473 nm, single transverse, low power laser beam via diffraction patterns (DPs), and Z-scan techniques. As high as 5.49 × 10−11 m2/W of nonlinear refractive index due to the DPs technique has been obtained. Both the nonlinear refractive index and nonlinear absorption coefficient are estimated via the standard Z-scan methods. The all-optical switching, both static and dynamic, prove to occur in the HM (6) using two visible laser beams.

4H-SiC Wafer Surfaces Irradiated with Femtosecond Laser at Fluence below the LSFL Threshold

This study investigates the microstructural and surface compositional changes of 4H-SiC wafers irradiated with femtosecond lasers at fluences below the threshold for low-spatial frequency laser-induced periodic surface structures (LSFL). Using scanning electron microscopy, cross-sectional transmission electron microscopy, and X-ray photoelectron spectroscopy, we characterized the processed SiC surfaces. Our results demonstrate precise control over the oxide layer thickness on the SiC surface at low laser fluences, allowing for the removal of only a few nanometers. This precise modification holds potential for future applications in wafer bonding by enabling the creation of a shallow SiO2 layer on the SiC surface.

Realizing multimodal lithography effects by adjusting laser exposure power ranges for TeOx inorganic photoresist

Abstract Suboxide chalcogenide thin films like TeO x are promising inorganic lithography materials. Different from previous reports of single-mode lithography based on TeO x films at low laser power, this study proposes multimodal lithography effects at low, medium, and high laser power ranges. The TeO x films were fabricated by reactive magnetron sputtering, exhibiting super smooth surface with an RMS 0.33 nm. The lithographic performance was researched using a laser direct writing system with a wavelength of 780 nm. The experiment results showed that different kind of lithographic patterns were achieved by changing laser power ranges. At low exposure powers (5 mW to 9 mW), TeO x film transforms from amorphous to crystalline, generating patterns with single-trench since only the crystalline state dissolves in alkaline developers. At medium exposure powers (10 mW to 15 mW), the center of the laser spot that has greater power turns the film from amorphous to crystalline and then back to amorphous due to the rapid quenching process, while the outer region cools slowly to form crystalline, resulting in the patterns with double-trenches, with feature size 119 nm (about 1/7 λ). At high exposure powers (>16 mW), the laser power is capable of ablating the TeO x film, resulting in the ablation and redeposition patterns. Therefore, multimodal lithographic nano-patterns on the same TeO x photoresist film can be realized with only one lithography process by precisely manipulating the laser power ranges, which has significant implications in the fields of nano-manufacturing and optical storage.

In-band pumped erbium doped glass microspherical lasers

High-Q whispering gallery mode (WGM) microspherical resonators made in rare earth (RE) doped glasses are an ideal platform to implement compact and low threshold laser sources and represent a simple tool for the characterization of laser glasses and an ideal platform for several sensing applications. In the case of Erbium-doped glass, the conventional pumping is performed at 980 nm or at 1480 nm. In this work on erbium doped tellurite glass microspheres, we demonstrate WGM lasers with resonant pumping in the C telecom band using pump frequencies for which the absorption cross section is smaller than the emission cross section. Reduced thermal effects are observed, with laser emissions above 1600 nm.

Mechanism of shape memory effect alteration in Ni50.4Ti49.6 via laser powder bed fusion from the perspective of martensitic twin

ABSTRACT The phase transformation from martensitic twins to austenite phase in NiTi shape memory alloys (SMAs) determines their shape memory effect (SME). However, systematic studies are indeed needed to reveal which martensitic twin type is effective in enhancing the SME for NiTi SMAs due to the diversity of martensitic twins. In this work, based on laser powder bed fusion (LPBF) NiTi SMAs, an excellent strength-ductility combination of 900.5 MPa and 13.9% was obtained by utilising a low laser power (70 W) and scanning speed (200 mm/s), which represents one of the highest values attainable among current LPBF NiTi SMAs. Furthermore, based on transmission kikuchi diffraction, it is found that high-density { 11 1 ¯ } I-type martensitic twins enhanced the SME of LPBF NiTi SMAs significantly, and the maximum SME recovery ratio is 95.8% after 10 cycles at controlled strain (6%) cyclic tensile loading-unloading. Conversely, the formation of { 1 ¯ 11 } I-type martensitic twins in the matrix weakened the SME of LPBF NiTi SMAs remarkably and lost SME after 10 cycles at controlled strain (6%) cyclic tensile loading-unloading. This research offers some valuable insights into the relationship between martensitic twin and SME for LPBF NiTi SMAs and paves the new way for modulation of microstructure to enhance mechanical properties and SME for NiTi SMAs via LPBF.

Regenerative endodontic therapy in immature teeth using photobiomodulation and photodynamic therapy; a histomorphological study in canine model

BackgroundRegenerative endodontic therapy (RET) is still coming up short to demonstrate histological evidence for true regeneration with clinically feasible protocol of cell homing in single visit approach.AimThe aim of the present study is to evaluate the regenerative potential of photobiomodulation (PBM) on RET in immature roots when photodynamic therapy (PDT) protocol is implemented for root canal disinfection in canine model.Materials and methodsSeventy-two root canals were recruited, with sixty assigned to experimental groups and twelve to positive and negative controls. Following the induction of pulp necrosis and apical periodontitis, the roots were divided into two experimental groups: Group I received RET followed by PBM (seven sessions with an 808 nm diode laser at 300 mW for 90 s), and Group II received RET without PBM. Follow-ups were conducted at 1, 2, and 3 months (subgroups A, B, and C respectively). Qualitative and quantitative assessment was carried out histologically. All data were statistically analyzed with the Mann-Whitney U test and Bonferroni’s adjustment, as well as Chi square test.ResultsThe newly formed hard tissue highly resembled true dentine where the dentinal tubules looked well organized lined by poly layers palisading pattern of rounded odontoblast-like cells with cytoplasmic processes extending through the predentine layer. GI exhibited statistically significantly higher scores of vital tissue infiltration and hard tissue deposition in subgroups A and B (P ≤ 0.05). The inflammatory cells scores were significantly lower in GI than in GII at all time intervals. However, no significance could be detected regarding apical closure.ConclusionThe disinfection protocol of PDT and subsequent irradiation with low power laser in PBM protocol pose a promising potential for regenerative endodontics in immature teeth.

AlCrCuFeNi3 Dual‐Phase High‐Entropy Alloy Manufactured by Selective Laser Melting in Situ Alloying: Alloying Degree, Microstructure, and Strength

Herein, the Co‐free, low‐cost dual‐phase AlCrCuFeNi3 high‐entropy alloy (HEA) is successfully developed by in situ alloying induced by selective laser melting (SLM) technique from an initial mixture of Ni and AlCrCuFeNi alloy powders. The effect of process parameters on the microstructure and strength of the SLMed AlCrCuFeNi3 HEA is investigated. It is found that the degree of in situ alloying strongly depends on the laser power. Low laser power leads to insufficient in situ alloying, and a large amount of incompletely diffused Ni and body‐centered cubic (BCC) AlCrCuFeNi alloy powder blocks remain, forming the eutectic structure with alternating face‐centered cubic and BCC phases. With the increase in laser power, the degree of in situ alloying increases, resulting in a decrease in the number of BCC phases as well as the yield strength of the SLMed AlCrCuFeNi3 HEA. The highest yield strength of the SLMed AlCrCuFeNi3 HEA is obtained at low laser power (200 W–600 mm s−1), reaching 689.02 ± 17.54 MPa.

Impacts of hydroxyl and bond energy on laser‐induced damage in mid‐infrared chalcogenide glass

AbstractMid‐infrared chalcogenide glasses often suffer from a low laser damage threshold due to their weak bond energy and the presence of impurities, particularly at the specific wavelength of 2.94 µm, which is widely used in medical applications. In this paper, we first investigated the effect of the hydroxyl (OH⁻) peak absorption coefficient on the laser damage properties of As2S3 glasses. The surface temperature distribution of chalcogenide glasses under laser irradiation was also analyzed using the finite element method (FEM) and in‐situ heat monitoring. The results showed that the surface temperature of the glass increases exponentially with the rise in the absorption coefficient at the OH− peak position. Subsequently, Raman spectra analysis and average bond energy (ABE) theory were employed to compare five typical chalcogenide glasses without hydroxyl absorption, revealing the relationship between the laser damage threshold and the bond energies of the glass networks. Finally, an optimized glass composition of Ge25As10S65 was identified, possessing the highest laser damage threshold of 340.98 J/cm2, more than twice that of traditional As2S3. These findings provide essential glass host and data references for the future development of mid‐ and far‐infrared optical fibers and waveguide devices.

The Effectivity of Acemannan Sponge and Calcium Phosphate Cement-Calcium Sulfate Hemihydrate (CPC-CSH)-Diode Laser-Assisted Method on the Direct Pulp Capping

Dental caries, the decay of tooth, affects approximately 2.3 billion people worldwide and reaches 88.8% of the total Indonesians. Caries reaching the pulp requires direct pulp capping (DPC) therapy to preserve pulp vitality. Ca(OH)2 is the golden standard DPC material, but its adhesion and mechanical properties are poor. Therefore, an alternative therapy is needed to improve the success of DPC using acemannan sponge and calcium phosphate cement-calcium sulfate hemihydrate (CPC-CSH)-diode laser. Acemannan, polymannose extracted from aloe vera gel, plays a role in reparative dentin formation that is immunomodulatory, antimicrobial, biocompatible, and accelerates wound healing. Calcium Phosphate Cement (CPC), bioactive material used in tissue engineering. Calcium sulfate hemihydrate (CSH), inorganic component and biocompatible. The combination of CPC-CSH can shorten the setting time, maintain compressive strength, and has good handling properties. Low level diode laser (LLDL) plays a role in reparative dentin formation by altering growth factors expression to stimulate cell proliferation and fibroblast development. LLDL is applied before pulp capping material application between the pulp-dentin so that aggregated collagen fibrils are collected and stimulate the formation of odontoblasts. This paper aims to describe The Effectiveness of Acemannan Sponge and Calcium Phosphate Cement-Calcium Sulfate Hemihydrate (CPC-CSH)-Diode Laser Assisted Method in Direct Pulp Capping Therapy. Article searching uses the Preferred Reporting Items for Systematic Reviews and Meta-analyses with keywords (MeSH): "DPC and Acemannan", "DPC and CPC-CSH", and "DPC and Diode Laser" from Pubmed, ScienceDirect, and Google Scholar databases in 2019-2024. Acemannan Sponge and Calcium Phosphate Cement-Calcium Sulfate Hemihydrate (CPC-CSH)-Diode Laser Assisted Method are effective as Alternative Direct Pulp Capping Therapy.

Experimentation and FE analysis of low carbon steel-based laser welded tailored blanks in case of single point incremental forming

This study explores the formability of laser-welded tailored blanks in the context of single-point incremental forming (SPIF), a flexible and dieless manufacturing process. Two approaches, variation in materials and thicknesses, were used to fabricate tailor-welded blanks (TWB) with CRCA and DD steel sheets. The quality of the weld was evaluated by metallographic studies and tensile tests. The ductility of the welded joint was reduced by 81%, and the hardness was increased by 133% compared to the base metal. SPIF was employed using a hemispherical tool to form a ‘D’ shape geometry on fabricated TWBs. Fracture was observed only at the weld line, irrespective of thickness and material combination in the TWB. The forming height achieved from the SPIF of TWBs was reduced by 24% and 34% for both differences in thickness and material when compared to their corresponding base metals. Finite Element simulations were performed in Abaqus software using a dynamic explicit approach employing von Mises and Hill48 yield functions. Further, the FE model was validated by comparing the thickness and surface major/minor strains at the same forming height as observed from the experiments. Reduced formability and no weld line movement were the main observations made in this study, and the same was manifested by the FE simulation.

Whispering Gallery Mode Micro/Nanolasers for Intracellular Probing at Single Cell Resolution.

Intracellular probing at single cell resolution is key to revealing the heterogeneity of cells, learning new cell subtypes and functions, understanding the pathophysiology of disease, and ensuring precise diagnosis and treatment. Despite the best efforts, an enormous challenge remains due to the very small size, extremely low content, and dynamic microenvironment of a single cell. Whispering gallery mode (WGM) micro/nanolasers (active WGM) offer unique advantages of small mode volume, high quality factors, bright and low threshold laser emission, and narrow line width, particularly suitable for integration within a single cell. In this review, we provide a focused overview of WGM micro/nanolasers for intracellular probing. We deliver information on WGM micro/nanolaser concepts, sensing mechanism, and biocompatibility, as well as recent progress in intracellular probing applications mainly covering cellular-level sensing, molecular-level detection, and feasibility for cellular imaging. At the end, challenges and prospects of WGM micro/nanolasers for intracellular applications are discussed.

Optical properties of carbon dots generated in liquid by pulsed IR laser at 1064 nm

Biocompatible carbon dots (CDs) have been synthesized by the laser ablation of graphite and vegetable carbon (charcoal) placed in a phosphate-buffered saline (PBS) solution. The carbon nanoparticles are produced by a pulsed IR laser beam, operating at 1064 nm, 100 mJ energy, and 3 ns pulse duration, interacting with the carbon matrix placed in the liquid at a 0.2 Hz repetition rate. The ablation rate, in terms of removed carbon mass per laser shot, was evaluated to be about 75.8 ng/pulse and 758 ng/pulse for graphite and charcoal, respectively. Optical and electronic microscopy, UV-Vis spectroscopy, and luminescence measurements were employed to evince the CDs dispersion through its photoluminescence emission. The UV excitation at a 365 nm wavelength induces CDs luminescence in the visible region, as a result of electron transition, at a wavelength band depending on the laser spot size, i.e., of the laser fluence. CDs luminescence emission obtained from charcoal is independent of the laser fluence, showing a major emission peak around 475 nm and a secondary emission peak at 515 nm. CDs luminescence emission obtained from graphite depends on the laser fluence, showing a minor wavelength band, around 474 nm, at high laser fluences and a major wavelength band, around 670 nm, at low laser fluence. The CDs luminescence of the produced biocompatible solution finds many applications in the bio-medical field, as will be presented and discussed.

Preparation of gelatine calibration standards for LA-ICP-MS bioimaging with 266 nm laser ablation systems

Gelatine is the external standard matrix of choice for quantitative biomaging of elements and metal tags in tissue. Its ablation characteristics closely match that of tissue when using 193 and 213 nm lasers, but this has not been demonstrated at 266 nm. With the interest in 266 nm laser ablation systems growing due to the selective ablation of tissue over glass substrates, this gap needed to be investigated. Optical profilometry was used to map the line crater volumes of gelatine and murine brain and quadriceps tissues ablated with a 266 nm laser. Raw gelatine did not ablate in a similar manner to either tissue type and ultra-violet absorbent chemical additives were required to match ablation volumes. Addition of either 4 g L−1l-tryptophan or 3 g L−1 gallic acid was used to match the ablation volume of murine quadriceps. Murine brain tissue had an increased ablation volume over the quadriceps tissue (1400 ± 130 versus 1100 ± 160 μm3 at 1.5 J cm−2), and the addition of 5 g L−1 gallic acid and the use of low laser energy (≤1.5 J cm−2) was required to match the ablation of brain tissue. The modified standards were tested on a 213 nm laser, and the addition of either additive to gelatine did not affect ablation volume. The effect of additives on fractionation and two-phase sample transport was investigated, no fractionation was observed, and a decrease in two-phase sample transport of up to 60 % was obtained with the modified gelatine. This decrease was caused by the reduced laser energy required for ablation. Finally, the potential uses of optical profilometry as a standardisation tool are discussed.

A low quantum defect and power scalable Yb-doped glass waveguide laser

We present a continuous wave laser action in ytterbium (Yb)-doped phosphate glass buried channel waveguides. The 25 mm long waveguides were fabricated by the standard ion exchange method. When pumped with a 976 nm laser diode, the waveguide laser emits at 982.4 nm, yielding an ultralow quantum defect of 0.66 %. The impact of coupling and pump power variation on the laser emission wavelengths is demonstrated. Furthermore, the results of pulsing using a monolayer graphene as a saturable absorber (SA) are presented and a pulse train with a repetition rate of 1 MHz and a pulse width of 700 ns was obtained.

Addressable scanning multifocal structured illumination microscopy using acousto-optic deflectors.

Multifocal structured illumination microscopy (MSIM) is a popular super-resolution imaging technique known for its good probe compatibility, low laser power requirements, and improved imaging depth, making it widely applicable in biomedical research. However, the speed of MSIM imaging is typically constrained by the approaches employed to generate and scan the laser foci across the sample. In this study, we propose a flexible two-photon excitation MSIM method using a pair of acousto-optic deflectors. By adopting addressable scanning (AS) and synchronized capturing, MSIM super-resolution imaging can be performed in multiple discrete regions of interest (ROIs) within the field of view. Notably, this AS-MSIM scheme not only enhances the speed of MSIM imaging but also alleviates photobleaching and phototoxicity to biological samples. We demonstrate its potential by achieving super-resolution imaging of selected mitochondria within cells at a frame rate of 4 Hz. Furthermore, we deliberate the possibility of even faster imaging.

Plasmomagnetic hybrid gold nanostructures as multifunctional nanocarriers for drug delivery, MRI contrast, and photothermal therapy of drug-resistant cancer cells

Presenting a simple efficient method, plasmomagnetic hybrid nanostructures (PNIPAM coated gold nanorods-dexpion hybrid nanostructure, PN-GDHNs) capable of serving as dual drug nanocarriers, MRI contrast, and photothermal agents for cancer therapy were synthesized. The cisplatin (CDDP) and doxorubicin (DOX) were loaded on PN-GDHNs and tested for their drug release, cytotoxicity, photothermal, and MRI contrast in vitro. We found that the drug release was controlled by pH and temperature, and the cytotoxicity was enhanced by the combination of chemotherapy and photothermal therapy. We also found that the PN-GDHNs could overcome the drug resistance of MCF7 breast cancer cells and improve the MRI contrast. We achieved a high cancer cell-killing efficiency of 97.3 ± 0.4 % in one dose with low drug concentration and laser power. Our results suggest that PN-GDHNs are promising multifunctional nanocarriers for cancer therapy applications.

Micro-cracks generation and growth manipulation by all-laser processing for low kerf-loss and high surface quality SiC slicing.

Low kerf-loss and high surface quality silicon carbide (SiC) wafer slicing is key to reducing cost, improving productivity, and extending industrial applications. In this paper, a novel all-laser processing approach is proposed by combining laser micro-cracks generation and growth manipulation. The first high fluence pulsed laser is applied to generate micro-cracks inside SiC, which increases its laser energy absorption. The second low fluence pulsed laser achieves the manipulation of micro-cracks growth and interconnection to separate SiC wafer. The optimal laser processing parameters are obtained to separate a 4H-SiC substrate at a thickness of 500 µm. The sliced surface is clean with average surface roughness (Sa) of 186 nm, standard deviation of 0.037, and kerf-loss of 915 nm. This laser slicing approach can be applied for high-hardness transparent material separation.

Precise Nanoparticle Manipulation Using Femtosecond Laser Trapping.

Optical tweezers use strongly focused light for trapping, characterizing, and manipulating objects in the microscopic and nanoscopic regimes. However, fully understanding optical trapping at the nanoscale remains a significant challenge. This holds importance because the nanoscale is the frontier for numerous promising advancements, ranging from enhancing single-molecule investigations in biology to developing hybrid devices for nanoelectronics and photonics and exploring fundamental quantum phenomena in opto-mechanics. We report an experimental and theoretical study of nanoparticles of various sizes, showing the advantages of the immense peak power of ultrashort laser pulses over conventional optical tweezers. We also demonstrate highly stable trapping of nanoparticles for extended durations at low average laser power using femtosecond lasers.