Search Results (148)

Objectives: The aim of this study was to determine the differential temperature produced on ceramic implants using laser irradiation on a pulsed setting of intrabony defects in vitro. Methods: A ceramic (Zr) dental implant (Zeramex, 4.8 × 12 mm) was placed into a bovine bone block. A three-wall intrabony defect (6 × 4 × 3 mm) was created to mimic an osseous peri-implant defect. Thermocouples were placed on the apical and coronal areas to measure temperature changes (∆T) during 60 s of laser irradiation. The bovine block was heated to 37 °C, and the defect walls were irradiated with the CO₂ and Er,Cr:YSGG laser. The settings used were pulsed mode for both lasers, with 30 Hz and 1.5 W for the Er,Cr:YSGG laser and 70 Hz and 2 W for the CO₂ laser. The same laser settings were repeated at room temperature (RT, 23 °C). Twenty trials were performed for each experimental group at room and body temperature for assessment of ∆T. Paired t-test were used to compare the measurements between 37 °C and 23 °C for the Er,Cr:YSGG, and CO₂ laser, respectively. Results: The CO₂ laser resulted in the highest ∆T (°C) at the coronal (15.22 ± 0.28/8.82 ± 0.21) and apical (5.84 ± 0.14/2.30 ± 0.28) level when this laser was used in both room temperature and body temperature, respectively. The highest ∆T (°C) for the Er,Cr:YSGG laser at body temperature at the coronal thermocouple was 7.64 ± 0.55, while for the CO₂ laser, at body temperature was 8.82 ± 0.21. Conclusion: Within the limitations of our study, the use of CO₂ laser and Er,Cr:YSGG laser on peri-implant defects generally appears to be safe in treating peri-implant defects around zirconia implants in vitro. Full article

An analysis of the existing methods of sintering diamond-containing composites is presented. On the basis of mathematical modeling and experimental studies, the conditions of the laser liquid-phase sintering of diamond-containing composites under which they retain their strength are determined. The energy and technological parameters of the laser irradiation process are characterized, which determine the range of laser processing modes within which no oxidation and crack formation occur, and a high-quality composite with specified geometrical parameters is formed. It has been proven that composites consisting of synthetic diamond grains and a metal bond do not lose strength under the condition that the temperature during laser heating does not exceed 1600 °C and the exposure time is 0.3 s. Electron microscopy and X-ray diffractometry were used for experimental studies of the microstructure and phase composition of the sintered layers. A new design and manufacturing method for a drum-type abrasive tool with replaceable diamond inserts for grinding large-sized aircraft and shipbuilding products are proposed. Components of a laser technological complex for the implementation of the process of sintering the diamond-containing layer of the abrasive inserts of the drum have been developed. Full article

This paper focuses on the switching and modulation techniques of terahertz waves, develops ${\mathrm{VO}}_2$ thin-film materials with an SPP structure, and uses terahertz time-domain spectroscopy (THz-TDS) to study the semiconductor–metal phase transition characteristics of ${\mathrm{VO}}_2$ thin films, especially the photoinduced semiconductor–metal phase transition characteristics of silicon-based ${\mathrm{VO}}_2$ thin films. The optical modulation characteristics of silicon-based ${\mathrm{VO}}_2$ thin films to terahertz waves under different light excitation modes, such as continuous light irradiation at different wavelengths and femtosecond pulsed laser irradiation, were analyzed. Combining the optical modulation characteristics of silicon-based ${\mathrm{VO}}_2$ thin films with the filtering characteristics of SPP structures, composite structures of ${\mathrm{VO}}_2$ thin films with metal hole arrays, composite structures of ${\mathrm{VO}}_2$ thin films with metal block arrays, and silicon-based ${\mathrm{VO}}_2$ microstructure arrays were designed. The characteristics of this dual-function device were tested experimentally. The experiment proves that the ${\mathrm{VO}}_2$ film material with an SPP structure has a transmission rate dropping sharply from 32% to 1% under light excitation; the resistivity changes by more than six orders of magnitude, and the modulation effect is remarkable. By applying the SPP structure to the ${\mathrm{VO}}_2$ material, the material can simultaneously possess modulation and filtering functions, enhancing its optical performance in the terahertz band. Full article

This study aimed to comparatively evaluate the effects of various surface treatment protocols on the shear bond strength (SBS) between heat-polymerized polymethyl methacrylate (PMMA) and different CAD/CAM framework materials, including cobalt–chromium (Co–Cr) alloys, ceramic particle-reinforced polyetheretherketone (PEEK), and glass fiber-reinforced composite resin (FRC). A total of 135 disc-shaped specimens were prepared from Co–Cr, PEEK, and FRC materials. Surface treatments specific to each material, including airborne-particle abrasion, sulfuric acid etching, laser irradiation, plasma activation, and primer application, were applied. PMMA cylinders were polymerized onto the treated surfaces, and all specimens were subjected to 30,000 thermal cycles. SBS values were measured using a universal testing machine, and the failure modes were classified. The normality of data distribution was assessed using the Kolmogorov–Smirnov test, and the homogeneity of variances was evaluated using Levene’s test. Group comparisons were performed using the Kruskal–Wallis test, and Dunn’s post hoc test with Bonferroni correction was applied in cases where significant differences were detected (α = 0.05). The highest SBS values (~27–28 MPa) were obtained in the Co–Cr group and in the PEEK groups treated with sulfuric acid and primer. In contrast, the PEEK group with additional laser treatment exhibited a lower SBS value. The untreated PEEK group showed significantly lower SBS (~3.9 MPa) compared to all other groups. The Trinia groups demonstrated intermediate SBS values (16.5–17.4 MPa), which exceeded the clinically acceptable threshold of 10 MPa. SEM observations revealed material- and protocol-specific surface responses; plasma-treated specimens maintained topographic integrity, whereas laser-induced surfaces showed localized degradation, particularly following dual-step protocols. Fracture mode analysis indicated that higher SBS values were associated with cohesive or mixed failures. SEM observations suggested that plasma treatment preserved surface morphology more effectively than laser treatment. This study highlights the importance of selecting material-specific surface treatments to optimize bonding between CAD/CAM frameworks and PMMA. Sulfuric acid and primer provided strong adhesion for PEEK, while the addition of laser or plasma offered no further benefit, making such steps potentially unnecessary. Trinia frameworks also showed acceptable performance with conventional treatments. These findings reinforce that simplified conditioning protocols may be clinically sufficient, and indicate that FRC materials like Trinia should be more fully considered for their broader clinical potential in modern CAD/CAM-based prosthetic planning. Full article

Laser-induced exit surface damage of fused silica is a key bottleneck for its application in high-power laser devices. As low-temporal coherence light (LTCL) has garnered increasing attention for high-power laser-driven inertial confinement fusion, understanding LTCL-induced exit surface damage of fused silica becomes crucial for improving the output power capability of LTCL devices. In this study, we characterized damage on the exit surface of fused silica under LTCL irradiation and investigated the physical mechanism of temporal coherence affecting the laser-induced damage threshold (LIDT). The relationship between defect information and temporal coherence was explored using a defect analysis model, and the defect damage process and response to each incident lasers were captured using time-resolved methods and artificially fabricated defects. We elucidate the physical mechanism behind the lower LIDT under LTCL irradiation compared to single longitudinal mode (SLM) pulse lasers. This study not only provides the boundary condition for safe fused silica operation in high-power LTCL devices but also offers deeper insight into the physical properties of LTCL. Full article

In this study, an interconnection was formed between a Cu/SnAg pillar bump and an Ni-less surface-treated Cu pad through laser-assisted bonding (LAB), and its bonding characteristics were evaluated. The LAB process influences the bond quality and mechanical strength based on the laser irradiation time and laser power density. The growth of the intermetallic compound (IMC) in the joint cross-section was observed via FE-SEM analysis. Under optimized LAB conditions, minimal IMC growth and high bonding strength were achieved compared to conventional thermo-compression bonding (TCB) and mass reflow (MR) processes. As the laser irradiation time and laser power density increased, solder splashing was observed at bump temperatures above 300 °C. This is hypothesized to be due to the rapid temperature rise causing the flux to vaporize explosively, resulting in simultaneous solder splashing. With increasing laser power density, the failure mode transitioned from the solder to the IMC. Full article

The root walls of immature permanent teeth are often weak, thin, and short, making regenerative endodontic treatment (RET) necessary. The goal of RET is to create a favorable environment for further root development. A biomimetic approach is essential for thorough disinfection, followed by the preservation and potential stimulation of stem cells from surrounding tissue to enable root regeneration and continued development. The objective of this study was to assess temperature changes on the external root surface, structural alterations in the internal root walls following irradiation with a 940 nm diode laser, and the biocompatibility of stem cells from the apical papilla (SCAPs). Irradiation was performed with varying output powers (0.5 W, 1 W, 1.5 W, and 2 W) in continuous mode for 5 s over four consecutive cycles. Thermographic measurements during irradiation, the micro-CT analysis of root samples, and mitochondrial activity of SCAPs were evaluated. The heating effect correlated directly with a higher output power and thinner root walls. A 1 W output power was found to be safe for immature teeth, particularly in the apical third of the root, while 1.5 W could be safely used for mature mandibular incisors. Diode laser irradiation at 1 W and 1.5 W significantly stimulated SCAPs’ mitochondrial activity within 24 h post-irradiation, indicating a potential photobiostimulatory effect. However, no significant changes were observed at lower (0.5 W) and higher (2 W) output powers. The area of open tubular space inside the root canal was significantly reduced after irradiation, regardless of the applied power. Additionally, irradiation contributed to the demineralization of the dentin on the inner root walls. Future studies should explore the impact of irrigants used between irradiation cycles, the potential benefits of conical laser tips for more even energy distribution, and a thorough analysis of how disinfection protocols affect both the dentin structure and stem cell viability. Full article

This study presents the design, simulation, and experimental validation of six fundamental laser interferometer types: Sagnac, Mach–Zehnder, Michelson, Twyman–Green, Fizeau, and Fabry–Pérot. Using ZEMAX OpticStudio in non-sequential mode with the physical optics propagation (POP) algorithm, the simulations provide detailed insights into the optical performance of these interferometers. A direct comparison is made between the simulated and experimental fringe patterns, coherent irradiance distributions, and phase plots, demonstrating strong agreement and validating the accuracy of computational modeling for interferometric analysis. The Mach–Zehnder and Michelson configurations exhibit high adaptability and measurement precision, while the Fabry–Pérot interferometer achieves superior spectral resolution. Twyman–Green interferometry proves particularly effective in mapping surface irregularities for optical testing. The results confirm the reliability of ZEMAX OpticStudio for high-precision optical system design and analysis. The novelty of this work lies in the comparative study between ZEMAX simulations and experimental interferometric results, particularly fringe patterns and phase distributions. This approach provides a clearer understanding of interferometer performance and enhances the accuracy of optical metrology, offering valuable insights for both theoretical modeling and practical applications. Full article

This paper studied a multi-channel self-mixing interferometric vibration measurement system based on a vertical-cavity surface-emitting laser array. A 1 × 8 laser array was utilized to irradiate multiple positions of a vibrating target to establish independent measurement channels. The reflected light beams, carrying the vibration information of each position, were redirected back into the laser and coherently mixed with the original optical field, generating the self-mixing interference. The interferometric signals were measured by monitoring the junction voltage variations across the terminals of the VCSEL array. A denoising filtering method based on the variational mode decomposition with Hausdorff distance was proposed to improve the signal-to-noise ratio. Furthermore, the vibration waveforms of different positions were reconstructed using the Hilbert transform-based orthogonal phase demodulation technology. Both simulations on synthetic signals and experiments with real datasets were conducted to validate the feasibility and stability of the proposed method. Due to the array detection configuration, the system boasted a simple and compact structure, low power consumption, and easy extensibility, laying the groundwork for high accuracy and multi-dimensional vibration detection in industrial applications. Full article

To improve laser anti-UAV technology and UAV laser protection capabilities, research on continuous laser damage to a UAV flight control system has been carried out. Combining waveform and function monitoring, the performance of the flight control system under laser irradiation was observed in real time, and the temperature and ablation process were recorded, which were used to analyze its damage characteristics and thresholds. Our experimental results show that the flight control system had two damage modes: temporary failure and permanent damage. Temporary failure had a temperature threshold, which was on average $450.85$ K. All temporarily failed flight control system functions could be restored after cooling and a manual restart, but permanently damaged flight control systems could not be manually restarted. This experiment showed that, within K. All temporarily failed flight control system functions could be restored after cooling and a manual restart, but permanently damaged flight control systems could not be manually restarted. This experiment showed that, within $10 \mathrm{s}$, the power density required for temporary failure and permanent damage to the flight control system was ${28.4 \mathrm{W}/\mathrm{c}\mathrm{m}}^2$ and ${42.6 \mathrm{W}/\mathrm{c}\mathrm{m}}^2$, respectively. The power density required for permanent damage was ${82.0 \mathrm{W}/\mathrm{c}\mathrm{m}}^2$ within $16 \mathrm{s}$ if the flight control system was encapsulated with aluminum alloy. Based on the circuit fault diagnosis of the flight control system samples that has been permanently damaged, the laser’s thermal effects damaged the diodes and linear regulators, ultimately rendering the flight control system unable to be manually restarted. Full article

Background/Objectives: Oral candidiasis is an opportunistic infection caused by Candida species. Recently, antifungal drugs have become less effective due to yeast resistance, emphasizing the need for new treatment strategies. This study aimed to assess the effect of the Er:YAG laser on the inhibition of growth and elimination of mature single-species Candida biofilms. Methods: The study utilized reference strains of C. albicans, C. glabrata, C. parapsilosis, and C. krusei organized in single-species biofilms on Sabouraud dextrose agar (SDA). First part: Candida suspensions (0.5 McFarland standard) were spread on SDA plates—two for each strain. Er:YAG laser irradiation was applied in a single pulse mode, 30 to 400 mJ, to 32 predetermined points. The growth inhibition zones (GIZs) were measured at 24–96 h of incubation. Second part: biofilms were prepared similarly and, after 96 h of incubation, exposed to Er:YAG laser irradiation at different energies (50, 100, 150, 200 mJ) for 180 s, per 1.44 cm area. Post-irradiation, impressions were taken using Rodac Agar to determine yeast counts. The count of colony-forming units (CFU) after irradiation was measured and results were analysed statistically. Results: First part: GIZ was found in all irradiated sites, with various Candida strains. The results showed a significant increase in the width of GIZ in the energy range of 30–280 mJ and a non-significant increase in the energy range of 300–400 mJ. Second part: the number of CFU remaining after the irradiation of biofilms with 150 mJ energy differed statistically significantly from other results obtained after using 50, 100, or 200 mJ energy, regardless of the Candida strain tested. Conclusions: The Er:YAG is shown to have good disinfecting properties (inhibiting biofilm growth, even at low-energy doses (50 mJ), and eliminating maturity, Candida spp. biofilms most effective on the 150 mJ energy dose). Full article

The technical development of diode lasers with regard to wavelengths, output powers and pulse durations in the order of microseconds is expanding the range of medical applications. The 445 nm wavelength, in particular, offers a promising approach. Such a laser system is now available, and its technical and optical properties are introduced here. To characterize the diode laser with a wavelength of 445 nm, laser settings were recorded in both CW and pulse modes in the range µs to ms, with duty-cycles of 1% up to 40% (partially also up to 90%). At the same time, the temporal behaviour of the laser pulses was documented. In addition, the influence of different irradiation parameters for pulse durations of 10 µs, 100 µs and 1 ms at duty-cycles of 50%, 25% and 15% on porcine tissue was investigated. With regard to the cutting depth and thermal damage zones, cuts were carried out in the contact mode using an optical fiber with a core diameter of 375 µm and a cut speed of 3 mm/s. The average power was set between 2 W and 8 W. Output powers of up to 12.7 W in CW mode and peak powers > 30 W, with pulse durations of 5 and 10 µs, were achieved. Cuts with a depth of up to 1 mm could be created using 100 µs pulses with different duty-cycles and also in CW mode. The width of the thermal damage zone was between 200 and 350 µm for all settings. The 445 nm wavelength is characterized by a large number of possible advantages in surgical applications. Pulse durations down to the µs-range with peak power approximately three times higher than average power could open up new applications. Full article

In the realm of advanced optical fiber sensing (OFS) technologies, Fiber Bragg Grating (FBG) has garnered widespread application in the monitoring of temperature, strain, and external refractive indices, particularly within high-radiation environments such as high-energy physics laboratories, nuclear facilities, and space satellites. Notably, FBGs inscribed using femtosecond lasers are favored for their superior radiation resistance. Among various inscription techniques, the point-by-point (PbP) and line-by-line (LbL) methods are predominant; however, their comparative impacts on radiation durability have not been adequately explored. In this research, FBGs were inscribed on a single-mode fiber using both the PbP and LbL methods, and subsequently subjected to a total irradiation dose of 5.04 kGy (radiation flux of 2 rad/s) over 70 h in a ⁶⁰Co-γ radiation environment. By evaluating the changes in temperature- and strain-sensing performance of the FBG pre-irradiation and post-irradiation, this study identifies a more favorable technique for writing anti-irradiation FBG sensors. Moreover, an analysis into the radiation damage mechanisms in optical fibers, alongside the principles of femtosecond laser inscription, provides insights into the enhanced radiation resistance observed in femtosecond laser-written FBGs. This study thus furnishes significant guidance for the development of highly radiation-resistant FBG sensors, serving as a critical reference in the field of high-performance optical fiber sensing technologies. Full article

Plasmonic structural color originates from the scattering and absorption of visible light by metallic nanostructures. Stacks consisting of thin, disordered semicontinuous metal films are attractive plasmonic color media, as they can be mass-produced using industry-proven physical vapor deposition techniques. These films are comprised of random nano-island structures of various sizes and shapes resonating at different wavelengths. When irradiated with short-pulse lasers, the nanostructures are locally restructured, and their optical response is altered in a spectrally selective manner. Therefore, various colors are obtained. We demonstrate the generation of structural plasmonic colors through femtosecond laser modification of a thin aluminum film–isolator–metal mirror (TAFIM) structure. Laser-induced structuring of TAFIM’s top aluminum film significantly alters the sample’s specular and diffuse reflectance depending on the fluence value and the number of times a region is scanned. A “negative image” effect is possible, where a dark field observation mode image is a negative of a bright field mode image. This effect is visible using an optical microscope, the naked eye, and a digital camera. The use of self-passivating aluminum results in a long-lasting, non-fading coloration effect. The reported technique could be used in anti-counterfeiting and security applications, as well as in plasmonic color printing and macroscopic and microscopic marking for personalized fine arts and aesthetic products such as jewelry. Full article

Objective: The aim of this study was to evaluate the photothermal effect of a 970 nm diode laser on Enterococcus faecalis biofilms. Methods: 72 extracted human single-rooted teeth were prepared, sterilized, and inoculated with Enterococcus faecalis to establish a two-week-old biofilm. The specimens were divided into six groups (n = 12): Group 1 (G1)—negative control (PBS—no laser), Group 2 (G2)—positive control (1% NaOCl rinse—no laser), Group 3 (G3)—a 970 nm laser in 1.5 W pulse mode, Group 4 (G4)—a 970 nm laser in 2 W pulse mode, Group 5 (G5)—a 970 nm laser in 1.5 W continuous mode, Group 6 (G6)—a 970 nm laser in 2 W continuous mode. Bacterial viability was evaluated using the LIVE/DEAD BacLight kit and analyzed by flow cytometry (FCM). Temperature changes on the root surface during irradiation were analyzed using a K-type thermocouple. Data were statistically analyzed using one-way ANOVA and Tukey’s multiple comparison test (α = 0.05). Results: Bacterial viability was significantly reduced after laser irradiation in continuous mode using 1.5 W (21% of live bacteria) and 2 W (14% of live bacteria). When the pulsed mode was applied, the reduction in bacterial viability was less, with a mean survival of 53% (1.5 PF, whereas 29% of bacteria survived after 2 W irradiation). Conclusions: The 970 nm diode laser at 2 W continuous mode effectively reduced the viability of E. faecalis biofilms in root canals without causing unacceptable temperature rises at the root surface. Full article