Low-energy Laser Research Articles

A sensitivity-enhanced all-optical probe for non-contact laser ultrasonic inspection

Non-contact laser ultrasonic technique has been increasingly implemented for non-destructive inspections in harsh environments, high-temperature fields, and components having complex geometries. However, the poor signal-to-noise ratio and low amplitude of laser generated ultrasonic signals under a thermoelastic regime severely restrict its applications. Here, a sensitivity-enhanced all-optical probe was proposed for laser ultrasonic non-destructive testing. It consists of an optical sensor and an ellipsoidal acoustic cavity, where an optical sensor is placed at one focus of the cavity, and the detection point is set at another focus. The ultrasound signals are focused through the cavity and detected by the optical sensor. Side-by-side comparison experiments were carried out, and the results show that the probe can improve the signal amplitude by about 7.8 times compared to using a traditional optical sensor alone. The probe can make laser ultrasound detect defects with lower laser energy, which is of great significance to improve the efficiency of non-contact defect detection.

Экспериментальное обоснование использования 1% раствора гидроксипропилметилцеллюлозы для защиты эндотелия заднего послойного трансплантата роговицы при его выкраивании низкоэнергетическим фемтосекундным лазером по инвертированной методике

Purpose. To evaluate experimentally endothelial cell loss of animal's cornea during inverted posterior lamellar corneal graft preparation technique by low-energy femtosecond laser with and without ophthalmic viscosurgical device (OVD) – 1% hydroxypropyl methylcellulose (HPMC) solution application. Material and methods. Posterior lamellar corneal grafts were created using a femtosecond laser (FSL). In the control group (n=16), a few drops of corneal storage solution were applied to the endothelium just before applanation, in the experimental group (n=16) – 1% HPMС. The quality of the applanation were monitored using an integrated in laser OCT system. The endothelial viability was determined using live/dead cells assay and the grafts were examined on a confocal laser scanning microscope. The obtained images were analyzed to count live and dead endothelial cells (EC). To assess the state of collagen fibers of the stromal side of the graft, samples from the control and experimental groups were examined using a scanning electron microscope (SEM). Results. According to the OCT, in all samples of both groups, a flat profile of the contact zone between the laser head and the endothelial monolayer was observed during applanation. The difference between the number of live and dead ECs was statistically significant between both groups. There were 2854 [2819; 2879] live cells/mm² in the control group, and 3477 [3426; 3719] live cells/mm² in the experimental group (p<0.001). Thus, the number of dead ECs in the control group was 710 [649; 728] cells/mm² . The number of dead ECs in the experimental group was 402 [366; 427] cells/mm² (p<0.001). When analyzing the images obtained on a SEM, the preservation of the architectonics of the graft collagen fibers with their single defibrations in both groups was observed. Conclusion. Application of 1% HPMC provides protection for endothelial cells from damage during posterior laser dissection using an FSL. In the study group, the number of endothelial cells was 9.92% higher than in the control group. The presence of the OVD layer in the interface between the head of the FSL and the EC did not affect the formation of an effective laser cut and did not reduce the quality of the stromal surface of the graft. The inverted technique FSL cut using a 1% solution of HPMC on the surface of the endothelium may be recommended for use in clinical practice. Key words: endothelium, keratocytes, corneal transplantation, keratoplasty, posterior lamellar keratoplasty, femtosecond laser, ophthalmic viscosurgical device, hydroxypropyl methylcellulose, confocal microscopy, scanning electron microscopy

Minimum separation between two pump pulses for ultrafast double magnetization switching in GdFeCo

Femtosecond laser ultrafast thermally induced magnetization switching (TIMS) has also attracted much attention due to its ability to trigger a single switching at the picosecond timescale. Current studies have shown that after a TIMS excited by a laser pulse, excitation of the switch again via TIMS does not require equilibrium between the subsystems. In this work, the main investigation is on the various possible cases of magnetization dynamics in GdFeCo under two short-delayed pulse excitations, as well as the factors limiting the minimum separation for double TIMS. These conditions are relevant for the potential application of TIMS to memory devices as it affects both the speed limit at which rewritten data is available and demonstrates the importance of spatial confinement of a laser pulse to bit size. The results show that low energy and short pulse duration lasers are prerequisites for double TIMS in GdFeCo based on simulations of atomic spin dynamics. By changing the damping constants of the alloy, we can shorten the minimum pulse separation between two pump pulses for double TIMS to 2 ps to approach terahertz frequency of write/erase cycles.

Unveiling of incubation and absorption-enhanced effects occurring during multi-shot femtosecond laser ablation of aluminum and steel surfaces

Interactions between ultrafast lasers and metal targets are crucial in various laser micro/nano-machinings. However, the underlying incubation and absorption-enhancement mechanisms remain elusive, which hinders the quality control of laser processing. Herein, we studied the incubation effect and absorption enhancement during multi-shot femtosecond-laser ablations via combining experiments and hydrodynamic simulations, taking aluminum alloy and stainless steels as paradigm materials. Accumulation effects of heat and damage-induced deformation were revealed by the evolutions of microstructures induced by low-energy femtosecond lasers. The calculated ablation thresholds were reduced with shot number, demonstrating the incubation effect. Calculation of threshold fluence via crater diameter is better than ablation depth, because that the latter is determined by different parameters at low- and high-energy conditions. Experimental observations and hydrodynamic simulations indicated that the enhanced absorption could be attributed to several factors, including laser-induced surface micro/sub-micro structures, photoionization, and plasma evolutions.

A Proposal for the Use of a Fixed Low-Energy Selective Laser Trabeculoplasty for Open Angle Glaucoma.

Selective laser trabeculoplasty (SLT) has been in routine clinical use for over 20 years with millions of patients successfully treated and a low rate of clinically significant complications. The procedure requires the clinician to manually position the laser beam on the trabecular meshwork using a gonioscopy lens and to titrate the SLT laser energy based on the amount of pigmentation in the angle, as well as the observation of small bubbles produced by the laser effect. We propose that SLT energy titration is unnecessary either to achieve intraocular pressure (IOP) reduction or to minimize potential side effects. Ample evidence to support our proposal includes multiple clinical reports demonstrating comparable levels of IOP reduction resulting from different laser energies, a large variety of energy and other laser parameters used in commercially available SLT lasers, and the nature of the laser-induced changes in the trabecular meshwork tissue with respect to energy. Despite these variations in laser parameters, SLT consistently reduces IOP with a low complication rate. We propose that using low fixed energy for all patients will effectively and safely lower patients' IOP while reducing the complexity of the SLT procedure, potentially making SLT accessible to more patients.

Influence of laser shock peening on surface characteristics and corrosion behavior of zirconium alloy

Low energy laser shock peening (LE-LSP) with different energies was carried out at zirconium (Zr) alloy. Characterization and electrochemical corrosion behavior of Zr alloy after LE-LSP treatment were investigated. Results show that the surface profile of Zr alloy after LE-LSP treatment is rough due to the regular undulations on the surfaces. The hardness of Zr alloy increases after LE-LSP treatment because the grain size of Zr alloy is refined, and the plastic deformation generated on the surface induces the working hardening. A melting layer, plastic deformation layer, and transition layer are formed on Zr alloy after LE-LSP treatment. The dislocation entanglement is observed at the plastic deformation layer, which indicates that the dislocation slip is the main deformation mechanism of Zr alloy. The electrochemical corrosion resistance of Zr alloy after LE-LSP treatment is improved because of an increase in the grain boundary, which improves the activity of Zr alloy and is beneficial for forming passive films.

Efficacy of low energy fractional carbon dioxide laser therapy in management of post-surgical hypertrophic scars

Background: aberrant & accelerated wound-healing process that results in hypertrophic scarring causes extracellular matrix & collagen to deposit abnormally in the dermis. After tissue damage occurs, a defensive reaction called tissue repair occurs. Aim; in this review; we aimed to present the effectiveness of low-energy fractional carbon dioxide laser therapy in treating hypertrophic scars following surgery. Summary: A safe & effective approach for treating hypertrophic burn scars is fractional ablative CO2 laser therapy. Even though more treatment sessions have been necessary for satisfying outcomes, a big improvement can be seen after just one round of therapy. Combination therapy with other modalities can decrease the need for repetition of therapy as efficacy increases. Though, in some studies, combination therapy may shorten the duration of studied case downtime & in others, combination therapy may increase side effects. essential for laser energy setting needs to be adjusted for each hypertrophic scar condition. larger research population & longer follow-up period are recommended.

Comparison of the Effectiveness of Selected Physiotherapy Methods in the Treatment of Tennis Elbow Syndrome: a case report

Background: Tennis elbow is a common ailment with which patients present to the physiotherapy office. It is characterized by pain in the area of the attachment of the tendons of the extensor muscles of the wrist to the lateral epicondyle of the humerus and the proximal part of the extensor muscles of the wrist, reduced grip strength and limited function of the upper limb. The condition can result from trauma, but in most cases it is the result of overload, with factors such as degeneration and relative ischemia, repetitive grasping movements, scar tissue and contracture playing a role. In this case, there is a diagnosis including history, functional tests and palpation of structures within the lateral epicondyle of the humerus.Aim of the study: To compare and evaluate the effectiveness of selected physiotherapy methods used in the treatment of tendinopathy of the lateral epicondyle region of the humerus Case report: Medical cases of four men aged 40-55 years complaining of pain in the lateral epicondyle region of the humerus are presented. Palpation examination, functional tests and symptoms indicated that we were dealing with "tennis elbow syndrome." Treatment included low-energy laser ultrasound, low-frequency magnetic field, radial shock wave, nitrogen vapor cryotherapy, deep transverse massage (DTM) according to Cyriax.Conclusions: Among the selected physiotherapeutic methods, radial shock wave therapy and deep transverse massage according to Cyriax showed the greatest effectiveness.

Research on evolution process of full-layer incision of skin tissue under different laser incidences.

Considering difficulties of achieving vertical incidence of beam in different positions of skin, it is significant to study potential effects of incidence angles of laser on incisions. Surgical platform with a 1064 nm continuous fiber laser was established. Incident angle was adopted and real-time temperature fluctuations in laser operating area could be monitored. The rats were treated with laser at day 0 and day 3 after incision modeling, and H&E, Masson, Sirius Red, and Immuno-histochemical staining and enzyme-linked immunosorbent assay were adopted at day 3, 7, 14 to analyze the performance of healing. Laser with energy density of 67.54 J/mm2 can effectively accelerate wound healing in vivo, in which a laser with incident angle around 60° can effectively avoid scar hyperplasia. Therefore, the use of low energy laser with a small deflection angle has a good clinical application prospect in promoting wound healing.

Application of Combined Laser Irradiation in Postoperative Period in Patients with Complicated Hepatic Echinococcosis

The article presents an analysis of the results of surgical treatment of patients with complicated liver echinococcosis in 102 patients using laser technology in the postoperative period. The patients were divided into 2 groups. Group I 62 (61%) patients with the use of laser technology in the postoperative period. II group 40 (39%) patients with the traditional method. Due to the use of low-energy lasers in the postoperative period with complicated liver echinococcosis, the proportion of complications was reduced by 3-3.5 times, and the duration of inpatient treatment was reduced by 1.5-2 times

The Finite Element Analysis on the Effects of Overlapping Rate in Low-Energy Laser Shock Peening

Laser shock peening has been widely studied and pioneeringly applied in aerospace industry as a life-extension technology for structured mechanical components. However, in other promising fields such as nuclear power industry, little has been studied concerning such critical issues as long-distance transmission of the laser beam by optical fiber and optimized parameters of typically low pulse energy with micrometer-sized beam spots. In such scenario, the overlapping rate between adjacent small spots plays a critical role in obtaining homogenous residual stress and surface morphology. In this study, a three-dimensional finite element model in AISI 420 martensitic stainless steel has been developed to correlate the residual stress as well as surface morphology with varying overlapping rates. Multiple laser spots are loaded with VDLOAD user subroutine in Abaqus. The residual stress distribution is analyzed with respects of laser shocking and in-depth planes. And the surface morphology is evaluated in terms of depression depth as well as surface roughness. Combined results suggest that the overlapping rate of 61% as an optimized value, which can be used as a basis for future experimental studies and industrial applications.

Exploring the Effects of Low-Level Laser Therapy on the Cytocompatibility and Osteo/Odontogenic Potential of Gingival-Derived Mesenchymal Stem Cells: Preliminary Report

Numerous tissue engineering uses for gingival-derived mesenchymal stem cells (GMSCs) have been demonstrated. Recently, low-level laser therapy (LLLT) has been projected as a factor that can improve MSCs’ regeneration capacity. Therefore, the aim of this research was to examine the impact of LLLT at 1.5 J/cm2 and 3 J/cm2 on the viability and osteo/odontogenic potential of GMSCs. An MTT assay was performed to detect viability. Osteo/odontogenic differentiation was evaluated using Alizarin Red S staining and qRT-PCR for the evaluation of the RUNX2, OC, DMP1, and DSPP genes. A two-way ANOVA with Tukey’s post hoc test was used to determine the statistical significance between groups. The results revealed that LLLT of both energy densities had no cytotoxic effect on GMSC viability. LLLT of 1.5 J/cm2 demonstrated better viability than the higher energy density (3 J/cm2). Furthermore, the osteo/odontogenic differentiation potential was promoted following LLLT radiation, where both groups exhibited mineralized nodule formation, with the low-energy laser having a significantly higher Alizarin Red S stain level. A qRT-PCR analysis revealed higher expression levels of osteogenic and odontogenic markers in the LLLT groups compared to the control group. In conclusion, this study showed the potential application of LLLT as a non-toxic and effective strategy to enhance the regenerative capacity of GMSCs for tissue engineering and clinical treatments in the oral and craniofacial fields.

Effect of an low-energy Nd: YAG laser on periodontal ligament stem cell homing through the SDF-1/CXCR4 signaling pathway

BackgroundThe key to the success of endogenous regeneration is to improve the homing rate of stem cells, and low-energy laser is an effective auxiliary means to promote cell migration and proliferation. The purpose of this study was to observe whether low-energy neodymium (Nd: YAG) laser with appropriate parameters can affect the proliferation and migration of periodontal ligament stem cells (PDLSCs) through SDF-1/CXCR4 pathway.Methodsh PDLSCs were cultured and identified. CCK8 assay was used to detect the proliferation of h PDLSCs after different power (0, 0.25, 0.5, 1, and 1.5 W) Nd: YAG laser (MSP, 10 Hz, 30 s, 300 μ m) irradiation at 2th, 3rd,5th, and 7th days, and the optimal laser irradiation parameters were selected for subsequent experiments. Then, the cells were categorized into five groups: control group (C), SDF-1 group (S), AMD3100 group (A), Nd: YAG laser irradiation group (N), and Nd: YAG laser irradiation + AMD3100 group (N + A). the migration of h PDLSCs was observed using Transwell, and the SDF-1 expression was evaluated using ELISA andRT-PCR. The SPSS Statistics 21.0 software was used for statistical analysis.ResultsThe fibroblasts cultured were identified as h PDLSCs. Compared with the C, when the power was 1 W, the proliferation rate of h PDLSCs was accelerated (P < 0.05). When the power was 1.5 W, the proliferation rate decreased (P < 0.05). When the power was 0.25 and 0.5 W, no statistically significant difference in the proliferation rate was observed (P > 0.05). The number of cell perforations values as follows: C (956.5 ± 51.74), A (981.5 ± 21.15), S (1253 ± 87.21), N (1336 ± 48.54), and N + A (1044 ± 22.13), that increased significantly in group N (P < 0.05), but decreased in group N + A (P < 0.05). The level of SDF-1 and the expression level of SDF-1 mRNA in groups N and N + A was higher than that in group C (P < 0.05) but lower than that in group A (P < 0.05).ConclusionsNd: YAG laser irradiation with appropriate parameters provides a new method for endogenous regeneration of periodontal tissue. SDF-1/CXCR4 signaling pathway may be the mechanism of LLLT promoting periodontal regeneration.

Safety and efficacy of cataract surgery performed with a low-energy femtosecond laser compared with conventional phacoemulsification in Chinese patients: a randomized clinical trial

BackgroundTo compare the safety and efficacy of femtosecond laser-assisted cataract surgery (FLACS) performed with the low-energy FEMTO LDV Z8 (Ziemer Ophthalmic Systems AG, Port, Switzerland) laser compared with conventional phacoemulsification (CP) in Chinese patients.MethodsThis prospective, multicenter, interventional study included 126 patients who were randomized (1:1) to undergo either FLACS or CP followed by intraocular lens (IOL) implantation between January 2019 and April 2020. The primary endpoint included the comparison of the endothelial cell loss (ECL) between the two groups at 3 months. Secondary endpoints included the comparison of cumulative dissipated energy (CDE), change in central corneal thickness (CCT) from baseline, and postoperative uncorrected and corrected distance visual acuities (UDVA and CDVA) in the two groups.ResultsAt all postoperative time points, the FLACS group was found to be non-inferior to CP for the mean ECL (− 409.3 versus − 436.9 cells/mm2 at 3 months) and mean CDE (4.1 versus 4.5 percent-seconds). The increase in CCT was significantly lower in the FLACS group compared with the CP group at Day 7 (4.9 versus 9.2 µm; P = 0.04); however, the difference was not statistically significant at 1 and 3 months. Postoperatively, mean UDVA and CDVA were comparable between the two groups. No intraoperative complications occurred.ConclusionsCataract surgery performed with a low-energy femtosecond laser was non-inferior to CP; however, the FLACS group had a statistically significantly lower increase in CCT at Day 7 compared with CP.Trial registration This trial is registered at ClinicalTrials.gov on May 15, 2019, with trial registration number: NCT03953053.

Non-surgical treatments for androgenetic alopecia: a literature review

Androgenetic alopecia is the most common type of hair loss and affects at least 80% of men and half of women before the age of 70, with the incidence increasing with age. Androgenetic alopecia is an ailment conditioned by genetic and hormonal factors, associated with excessive stimulation of the androgen receptor in the cells of the hair follicle. With the development of medicine, more and more therapeutic methods for androgenetic alopecia appear on the market, including minoxidil, 5-α-reductase inhibitors, microneedling, platelet-rich plasma, low-energy laser therapy, rosemary oil, or siRNA. Thanks to the constantly growing amount of scientific research, progressively more is known about the mechanisms of androgenetic alopecia development and potential strategies to stop it. The article analyzes the literature using electronic databases and textbooks to compile methods that can be an effective alternative for people who do not want to undergo surgery. Some of the methods presented in the article have the potential to not only slow down, but also reverse the progression of the disease. However, each of them still has its limitations.

Modern aspects of diagnosis and treatment of subjective manifestations and accommodation disorders in patients — professional users of personal computers (systematic review)

A systematic review was performed in the RSCI and PubMed databases using the following keywords: Computer vision syndrome, Digital eye strain, Accommodation, Accommodative asthenopia, RTS, and Quality of life. Eligible articles were evaluated in accordance with the criteria for prospective or retrospective studies. A total of 792 sources were analyzed, further using systematic review filters and authors knowledge of the topic. The retrospective analysis spanned 7 years (20162022). Data indicated that accommodative asthenopia (AA), as a functional visual disorder, is a natural state of the accommodative system of the eye caused by long-term exposure to visually intense work on a personal computer. AA is characterized by a wide range of subjective manifestations (complaints) and indicators of the examination of the patients vision, associated primarily with objective accommodation. A differentiated approach to the diagnosis of various forms of AA, such as habitual excessive stress of accommodation and asthenic form of accommodative asthenopia, is important to provide adequate treatment based on methods with direct physical effects on the eye (such as low-energy laser radiation, magnetophoresis, and stimulation of accommodation), opto-reflex treatment, and an outpatient course as part of home training.

Laser induced diamond/graphite structure for all-carbon deep-ultraviolet photodetector

Graphite was formed by in-situ structural conversion from sp3 to sp2 hybridized carbon via KrF excimer. The surface morphology of diamond was changed to nanoparticles after laser irradiation. Raman peak related to amorphous carbon emerged after laser treatments with energy of 10 ∼ 25 mJ cm−2. X-ray photoelectron spectroscopy exhibited that surface graphitization could take place under low laser energy of 2 mJ cm−2. The structural transformation of diamond after laser irradiation was further studied by cross-sectional transmission electron microscopy (TEM) analysis. The TEM results displayed that the diamond/graphite interface was gradually transformed from diamond to graphite, and the transformation process was verified by molecular dynamics simulations. The specific contact resistance of 7.83 × 10-5 Ω cm2 for the diamond/graphite structure was acquired by transmission line model. Meanwhile, the barrier height of the graphite/diamond contact was obtained to be 0.54 eV. In the end, an all-carbon deep-ultraviolet photodetector with diamond/graphite structure was developed. The all-carbon photodetector exhibited relatively high responsivity of 15 mA/W under 220 nm illumination, and a fast transient response of 86 μs.

Correlating laser energy with compositional and atomic-level information of oxides in atom probe tomography

Atom probe tomography (APT) is a 3D analysis technique that offers unique chemical accuracy and sensitivity with sub-nanometer spatial resolution. There is an increasing interest in the application of APT to complex oxides materials, giving new insight into the relation between local variations in chemical composition and emergent physical properties. However, in contrast to the field of metallurgy, where APT is routinely applied to study materials at the atomic level, complex oxides and their specific field evaporation mechanisms are much less explored. Here, we perform APT measurements on the hexagonal manganite ErMnO3 and systematically study the effect of different experimental parameters on the measured composition and structure. We demonstrate that both the mass resolving power (MRP) and compositional accuracy can be improved by increasing the charge-state ratio (CSR) working at low laser energy (< 5 pJ) for a given fixed detection rate. Furthermore, we observe a substantial preferential retention of Er atoms, which is suppressed at higher CSRs. We explain our findings based on fundamental field evaporation concepts, expanding the knowledge about the impact of key experimental parameters and the field evaporation process in complex oxides in general.

Control of resistive switching type in BaTiO3 thin films grown by high and low laser fluence

A ferroelectric memristor has attracted much attention due to convenient controlling by polarization switching, but the resistive switching has been attributed to the drift or charge trapping of defects. To distinguish the resistive switching mechanism between ferroelectric polarization switching and the normal resistive switching mechanism such as the drift or charge trapping of defects, BaTiO3 (BTO) thin films were grown on a (001) Nb:SrTiO3 single crystal substrate by pulsed laser deposition with high and low laser energy density. Based on a piezoelectric force microscope, ferroelectricity is found in BTO thin films grown at high laser energy density. X-ray photoelectron spectroscopy further confirms the existence of defects in the BTO films grown at low laser energy density. The high energy sample with low density of defects exhibits a resistance hysteresis loop but little current hysteresis loop, while the low energy sample with high density of defects shows a significant resistance and current hysteresis loop simultaneously. These results provide a deep understanding about the resistive switching from ferroelectric polarization switching and the drift or charge trapping of defects.

Early dynamics of laser-induced plasma and cavitation bubble in water

The knowledge of early laser-induced plasma and cavitation bubble dynamics are of great importance for a better understanding of underwater laser-induced breakdown spectroscopy. In this work, we investigated the temporal evolution of the plasma and bubble at an early stage before 2 μs, by using fast imaging and shadowgraph techniques. It showed that the initial plasma forms at the laser focal point and then grows up toward the incident laser. As time evolves, the plasma expands simultaneously forward and backward to its peripheral region and a sub-plasma structure can be observed at low laser energies. The plasma has a good pulse-to-pulse repeatability during the laser pulse, while soon after the laser pulse (from 20 to 50 ns), it undergoes a severe pulse-to-pulse fluctuation with an inhomogeneous emission distribution. At longer times, the plasma becomes much stable again. To clarify the interrelationship between the bubble dynamics and the plasma characteristics, shadowgraph images of the bubble were shown and compared with the plasma images. It showed that the morphology of the bubble and its evolution have a good consistency with the morphology of plasma. The bubble radius as a function of time can be well expressed by the equation R=at0.4, and a is a constant related to the laser energy. By inspecting the evolution curve of the bubble wall and the bubble pressure calculated based on the Gilmore model, a transition phase from 20 to 50 ns can be identified between the moving breakdown phase and the thermal expansion phase. In this transition phase, both the bubble expansion speed and the bubble pressure drop drastically that may account for the severe plasma fluctuations as observed in this period. These results of early bubble dynamics provide insights into the critical role of bubble-plasma interaction on the characterization of laser-induced plasma in water.