Search Results (314)

Recently, diffractive optics systems have garnered increasing attention due to their myriad benefits in various applications, such as creating vortex beams, Bessel beams, or optical traps, while refractive optics systems still exhibit some disadvantages related to materials, substrates, and intensity shapes. The manufacturing of diffractive optical elements has become easier due to the development of lithography techniques such as direct laser writing, photo lithography, and electron beam lithography. In this paper, we improve the results from previous research and propose a new methodology to design and fabricate advanced binary diffractive optical elements that achieve a square focal spot independently, reducing reliance on additional components. By integrating a binary square zone plate with an axicon zone plate of the same scale, we employ machine learning for laser path optimization and direct laser lithography for manufacturing. This streamlined approach enhances simplicity, accuracy, efficiency, and cost effectiveness. Our upgraded binary diffractive optical elements are ready for real-world applications, marking a significant improvement in optical capabilities. Full article

We report on the welding of optical borosilicate glass to an unpolished copper substrate (surface Ra of 0.27 µm and Rz of 1.89 µm) using bursts of femtosecond laser pulses. The present paper puts forth the hypothesis that glass–metal welding with a gap is contingent upon the ejection of molten jets of glass. We have ascertained the impact of pulse energy and focal position on weldability. This finding serves to substantiate our initial hypothesis and provides a framework for understanding the conditions under which this hypothesis is applicable. Under optimal conditions, but without the assistance of any clamping system, our welded samples maintained a breaking resistance of up to 10.9 MPa. Full article

To improve the accuracy of three-dimensional (3D) reconstruction under microscopic conditions for laser-induced breakdown spectroscopy (LIBS), this study developed a novel visual platform by integrating an industrial CCD camera with a microscope. A customized microscale calibration target was designed to calibrate intrinsic and extrinsic camera parameters accurately. Based on the pinhole imaging model, disparity maps were obtained via pixel matching to reconstruct high-precision 3D ablation morphology. A mathematical model was established to analyze how key imaging parameters—baseline distance, focal length, and depth of field—affect reconstruction accuracy in micro-imaging environments. Focusing on trace element detection in WC-Co alloy samples, the reconstructed ablation craters enabled the precise calculation of ablation volumes and revealed their correlations with laser parameters (energy, wavelength, pulse duration) and the physical-chemical properties of the samples. Multivariate regression analysis was employed to investigate how ablation morphology and plasma evolution jointly influence LIBS quantification. A nonlinear calibration model was proposed, significantly suppressing matrix effects, achieving R² = 0.987, and reducing RMSE to 0.1. This approach enhances micro-scale LIBS accuracy and provides a methodological reference for high-precision spectral analysis in environmental and materials applications. Full article

Wide-beam laser direct energy deposition (LDED) has been widely used due to its superior deposition efficiency. To achieve optimal laser-powder coupling, this technique typically employs rectangular powder nozzles. This study establishes a simulation model to systematically investigate the powder flow field characteristics of rectangular symmetric nozzles. Through parametric analysis of powder feeding rate, carrier gas flow rate, and shielding gas flow rate, the effects on powder stream convergence behavior are quantitatively evaluated to maximize powder utilization efficiency. Key findings reveal that, while the powder focal plane position is predominantly determined by nozzle geometry, powder feeding parameters exhibit negligible influence on flow field intersections. The resulting powder spot demonstrates a rectangular profile slightly exceeding the laser spot dimensions, and the powder concentration exhibits a distinctive flat-top distribution along the laser’s slow axis, contrasting with a Gaussian distribution along the scanning direction. Experimental validation through powder collection tests confirms strong agreement with the simulation results. Furthermore, a mathematical model was developed to accurately describe the powder concentration distribution at the focal plane. These findings provide fundamental theoretical guidance for optimizing powder feeding systems in wide-beam LDED applications. Full article

This study presents the optimization of a laser ablation process designed to achieve the precise removal of polyamide coatings from ultra-thin platinum wires. Removing polymer coatings is a critical challenge in high-reliability manufacturing processes such as aerospace thermocouple fabrication. The ablation process must not only ensure the complete removal of the polyamide insulation but also maintain the tensile strength of the wire to withstand mechanical handling in subsequent manufacturing stages. Additionally, the exposed platinum surface must exhibit low surface roughness to enable effective soldering and be free of thermal damage or residual debris to pass strict visual inspections. The wires have a total diameter of 65 µm, consisting of a 50 µm platinum core encased in a 15 µm polyamide coating. By utilizing a UV laser with a wavelength of 355 nm, average power of 3 W, a repetition rate range of 20 to 200 kHz, and a high-speed marking system, the process parameters were systematically refined. Initial attempts to perform the ablation in an air medium were unsuccessful due to inadequate thermal control and incomplete removal of the polyamide coating. Hence, a water-assisted ablation technique was explored to address these limitations. Experimental results demonstrated that a scanning speed of 1200 mm/s, coupled with a line spacing of 1 µm and a single ablation pass, resulted in complete coating removal while ensuring the integrity of the platinum substrate. The incorporation of a water layer above the ablation region was considered crucial for effective heat dissipation, preventing substrate overheating and ensuring uniform ablation. The laser’s spot diameter of 20 µm in air and a focal length of 130 mm introduced challenges related to overlap control between successive passes, requiring precise calibration to maintain consistency in coating removal. This research demonstrates the feasibility and reliability of water-assisted laser ablation as a method for a high-precision, non-contact coating material. Full article

The aim of this study is to solve the problem of it being difficult to obtain quantitative step signals when testing the time constant of thermocouples using the laser excitation method, thereby restricting the accuracy and repeatability of the test of the time constant of thermocouples. This paper designs a thermocouple time constant testing system in which laser power can be adjusted in real time. The thermocouple to be tested and a colorimetric thermometer with a faster response speed are placed on a pair of conjugate focal points of an elliptic mirror. By taking advantage of the aberration-free imaging characteristic of the conjugate focus, the temperature measured by the colorimetric thermometer is taken as the true value on the surface of the thermocouple so as to adjust the output power of the laser in real time, make the output curve of the thermocouple reach a steady state, and calculate the time constant of the thermocouple. This paper simulates and analyzes the effects of adjusting PID parameters using quantum neural networks. By comparing this with the method of optimizing PID parameters with BP neural networks, the superiority of the designed QNN-PID controller is proven. The designed controller was applied to the test system, and the dynamic response curves of the thermocouple reaching equilibrium at the expected temperatures of 800 °C, 900 °C, 1000 °C, 1050 °C, and 1100 °C were obtained. Through calculation, it was obtained that the time constants of the tested thermocouples were all within 150 ms, proving that this system can be used for the time constant test of rapid thermocouples. This also provides a basis for the selection of thermocouples in other subsequent temperature tests. Meanwhile, repeated experiments were conducted on the thermocouple test system at 1000 °C, once again verifying the feasibility of the test system and the repeatability of the experiment. Full article

Background/Objectives: Focal therapy (FT) and technology are closely connected. Advanced imaging allows for precise identification of the index lesion, enabling the targeted use of various thermal and non-thermal energy sources through different approaches, with specific techniques tailored to lesion location and operator expertise. This personalized approach enhances both safety and effectiveness, facilitating customized treatment planning. Methods: The International Consultation on Urological Diseases formed a committee to review the current literature on FT for prostate cancer (PCa), focusing specifically on the technique. Following in-depth discussions, the committee chose a “by lesion” approach rather than the traditional “by energy” approach to structure the review. A comprehensive PubMed search was conducted to gather relevant articles on the various energy modalities and procedural approaches used in FT for PCa. Results: Lesions in the apex, anterior, and posterior regions of the prostate can be accessed through several FT approaches, each associated with specific energy modalities and techniques. The transrectal approach utilizes high-intensity focused ultrasound (HIFU) and focal laser ablation (FLA), while the transperineal approach is compatible with energy sources such as cryotherapy, irreversible electroporation (IRE), brachytherapy, and FLA. The transurethral approach supports methods such as transurethral ultrasound ablation (TULSA). Each approach offers distinct advantages based on lesion location, treatment area, and energy modality. The choice of technique evaluated the safety and efficacy of each energy source and approach based on specific treatment areas within the prostate, highlighting the need for robust research across lesion locations and modalities, rather than focusing solely on each modality for a specific region. Conclusions: FT is rapidly advancing with new energy sources, technological improvements, and increasing operator expertise. To further optimize FT, research should prioritize evaluating the safety and effectiveness of different energy sources for various lesion locations, focusing on the treatment area rather than the energy modality itself. Full article

Background: Focal therapy has emerged as a viable alternative to radical prostate cancer treatment, offering oncologic control while minimizing morbidity. EchoLaser focal laser ablation (FLA) is a minimally invasive technique that utilizes high-precision laser energy for tumor destruction. This study evaluated the oncologic outcomes, procedural efficiency, and safety of EchoLaser focal therapy, comparing fiducial-assisted (FM+) and non-fiducial (FM−) approaches. Methods: A retrospective cohort study was conducted at Athens Medical Center, Greece, including 50 patients with localized prostate cancer treated with EchoLaser therapy. Patients were categorized into FM+ (n = 31) and FM− (n = 19) groups. Oncologic control (MRI and PSA levels at six months), procedural efficiency (operative time), and safety (adverse events) were assessed. Results: At six months, 80% of patients (n = 40) had no residual disease on MRI, while 20% (n = 10) showed persistent or recurrent tumor activity. PSA levels declined from 10.26 ± 14.99 ng/mL to 2.70 ± 2.67 ng/mL, reflecting a 74% median reduction. Procedure time was shorter in FM+ patients (33.48 ± 2.41 min vs. 45.79 ± 2.92 min, p < 0.01). Adverse events occurred only in the FM− group, including one case of urinary retention. Conclusions: FLA with EchoLaser using fiducial marker enhances procedural efficiency and could have a positive impact on oncologic control. These findings suggest that fiducial markers should be integrated into focal therapy protocols. Longer follow-up studies are needed to confirm the long-term outcomes. Full article

Multi-focal microlens arrays provide notable advantages over mono-focal counterparts, such as multi-scale imaging capabilities and optical aberration correction. However, existing multi-focal microlens arrays fabricated on continuous surfaces are incapable of achieving confocal imaging. As a result, multiple focus adjustments are required to acquire comprehensive image data, thereby complicating system design and increasing operational duration. To overcome this limitation, a stepped confocal surface microlens array is proposed, capable of simultaneously capturing images with multiple depths of field, various field-of-view scales, and different resolutions—without the need for additional focus adjustments. A combination of femtosecond laser processing and chemical etching was employed to fabricate microlenses with varying curvatures on a stepped fused silica substrate, which was subsequently used as a mold. The final stepped confocal microlens array was replicated via polydimethylsiloxane (PDMS) molding. Preliminary experimental analyses were carried out to determine the relationship between processing parameters and the resulting focal lengths. By precisely controlling these parameters, the fabricated stepped confocal microlens array successfully enabled confocal imaging, allowing for the simultaneous acquisition of diverse image data. This microlens array shows great potential in advancing lightweight, integrated, and highly stable optical systems for applications in optical sensing, spatial positioning, and machine vision. Full article

Background: The current animal models of multiple sclerosis (MS) predominantly emphasize white matter inflammation, reflecting early-stage disease. However, progressive MS (PMS) is characterized by cortical pathology, including subpial demyelination, chronic meningeal inflammation, and microglial activation, which are underrepresented in the existing models. While alternative mouse models replicate the relapsing–remitting phenotype and gray matter pathology, pathology is frequently dispersed throughout the brain, complicating the analysis of the specific lesion sites. Methods: To address this gap, we developed a novel model that integrates laser-induced focal demyelination with cytokine-driven meningeal inflammation to replicate the key aspects of PMS cortical pathology. Results: Using two-photon laser irradiation, we induced controlled subpial cortical lesions in CX3CR1-GFP mice, leading to microglial activation, astrocytosis, and focal demyelination. The addition of IFNγ-expressing adenovirus to promote meningeal inflammation which resulted in prolonged glial responses, increased immune cell infiltration, and exacerbated demyelination, mimicking the PMS-associated pathology. Conclusions: This model provides a powerful tool to investigate the mechanisms underlying the cortical lesion development and immune-mediated neurodegeneration in PMS. By capturing the critical aspects of cortical pathology, it enables the evaluation of therapeutic strategies targeting neuroinflammation and demyelination, ultimately aiding in the development of new treatments of progression in PMS patients. Full article

Bessel beams occupy an important position in optical research due to their characteristics of long focal depth, self-healing ability, and diffraction-free propagation. Traditional methods for generating Bessel beams suffer from complexity, a large size, low uniformity, and limited NA. Metasurfaces are considered to be a new technology for the miniaturization of optical devices due to their ability to regulate optical fields at subwavelength scales flexibly. Here, we generated Bessel beams by a complex-amplitude (CA) metasurface. The polarization conversion efficiency was controlled by the geometric size, while the phase value from 0 to 2π was manipulated based on the Pancharatnam–Berry (PB) phase. This approach enabled precise control over the axial intensity distribution of the optical field, which facilitated the generation of sub-millimeter-scale Bessel beams. Axial light field control based on CA metasurfaces has great potential for applications in a variety of fields, such as particle manipulation, large-depth-of-field imaging, and laser processing. Full article

To address the problem of excessive ablation in conventional laser processing caused by the inhomogeneous energy distribution at the focal point, along with the inherent heterogeneity and surface irregularities of textile materials, a new method for laser printing elastic bandage fabrics was developed. We used flat top light sources, short focal field mirrors, and low power lasers instead of the Gaussian light sources, long focal field mirrors, and high-power lasers used in traditional methods. First, the sample was preheated, and the aspherical lens system was designed and simulated. Then, the physical and chemical properties of laser-processed elastic bandage fabrics were investigated. Finally, based on single-factor experiments, orthogonal experimental analysis was conducted to determine the optimal process parameters. The results show that the optimized optical path can effectively improve the uniformity of the temperature field during laser scanning and enhance focusing performance; as energy gradually accumulates, chemical bonds in polymer molecules break; when the elastic bandage fabric is in a highly elastic state, it exhibits appropriate breaking strength and color difference. The best parameters obtained from the single-factor experiment are as follows: laser power range of 25–34 W, scanning speed range of 2200–2800 mm/s, preheating temperature range of 125–200 °C. The best parameters obtained from the orthogonal experiment are as follows: laser power 28 W, scanning speed 2800 mm/s, and the preheating temperature 175 °C. Full article

This study aims to examine and optimize CO₂ laser cutting parameters—namely, laser power, cutting speed, and focal plane position—when applied to polypropylene material using an experimental methodology. This research aims to improve cutting quality, increase cutting speed, and reduce waste while adhering to sustainability objectives. To achieve these goals, a comprehensive experimental approach was employed, incorporating the Box–Behnken Design (BBD) based on the response surface methodology (RSM) to optimize the laser cutting process by evaluating the relationships between input parameters and output responses. Data were collected through a series of controlled experiments in which laser power (ranging from 30 to 60 W), cutting speed (ranging from 30 to 60 mm/s), and focal plane position (set at −3, 0, and +3 mm) were systematically varied. The responses, quantified regarding cut quality, include kerf width and the heat-affected zone (HAZ). Additionally, RSM was used to optimize the laser cutting process to improve kerf quality. The results indicated that cutting speed has an inverse effect on kerf width and HAZ, while laser power has a direct effect. Furthermore, the focal plane position was found to have the least impact on the output responses. The maximum kerf width and HAZ were observed at a minimum cutting speed of 30 mm/s and a maximum laser power of 60 W. Full article

The present paper deals with the study of the fluence rate over both healthy and tumor tissues in the presence of focal laser ablation (FLA). We propose new analytical solutions for a coupled partial differential equation (PDE) system, which includes the transport equation modeling of light penetration into biological tissue, the bioheat equation modeling the heat transfer, and its respective damage. The present work could be the first step toward knowledge of the mathematical framework for biothermophysical problems, as well as the main key to simplify the numerical calculations due to its zero cost. We derive exact solutions and simulate results from them. We discuss the potential physical contributions and present respective conclusions about the following: (1) the validity of the diffusion approximation of the radiative transfer equation; (2) the local behavior of the source of scattered photons; (3) the unsteady state of the fluence rate; and (4) the boundedness of the critical time of the thermal damage to the cancerous tissue. We also discuss some controversial and diverging hypotheses. Full article

The wavefront aberrations (WAs) of a laser beam produced by an optical parametric oscillator (OPO) have been measured using a Hartmann–Shack sensor. The OPO tuning operation requires changes in the device that might affect the shape of the wavefront beam as the illumination wavelength is being modified. Different output wavelengths in the range 550–850 nm were systematically analyzed in terms of WAs. The WA laser beam was fairly stable with time (changes of about 1%), independently of the wavelength. Moreover, WAs were non-negligible and nearly constant between 600 and 800 nm, but they noticeably increased for 550 (~90%) and 850 nm (~50%), mainly due to a higher astigmatism influence. The contributions of other higher-order terms such as coma and spherical aberration also present particular spectral dependences. To our knowledge, this is the first report of a spectral OPO laser beam characterization in terms of optical aberrations. It addresses a gap in OPO laser characterization of WAs and offers actionable insights for multi-wavelength applications. These results might be useful in applications ranging from micromachining procedures to biomedical imaging, where an optimized focal spot is required to increase the efficiency of certain physical phenomena or to enhance the quality of the acquired images. Full article