Comprehensive ablation study of near-IR femtosecond laser action on the titanium-based alloy Ti6Al4V: morphological effects and surface structures at low and high fluences

The surface of a titanium-based alloy Ti6Al4V was subjected to modifications by a near-IR femtosecond Ti:Sapphire laser, emitting at 775 nm pulses of 200 fs duration, in single-pulse and multi-pulse regimes, with up to 400 accumulated pulses, and pulse energies ranging from 2.5 to 250 $$\upmu $$ μ J. The whole range of induced effects is presented, from gentle ablation and pattern occurrence to substantial crater formation. Very observable laser-induced parallel periodic surface structures are reported, appearing both within the damage spot area, with low fluences, and at the peripheries of the craters, with higher fluences—but also on crater walls, and inside the crater structures. Damage threshold fluences $$({F}_{\mathrm{th}})$$ ( F th ) and the incubation factor $$(\zeta )$$ ( ζ ) were also determined. Graphic abstract

Semipolar {202̅1} GaN Edge-Emitting Laser Diode on Epitaxial Lateral Overgrown Wing

Edge-emitting laser diodes (LDs) were fabricated on a reduced dislocation density epitaxial lateral overgrown (ELO) wing of a semipolar {202̅1} GaN substrate, termed an ELO wing LD. Two types of facet feasibility studies were conducted: (1) “handmade” facets, wherein lifted-off ELO wing LDs were cleaved manually, and (2) facets formed on wafers through reactive ion etching (RIE). Pulsed operation electrical and optical measurements confirmed the laser action in the RIE facet LDs with a threshold current of ~19 kAcm−2 and maximum light output power of 20 mW from a single uncoated facet. Handmade facet devices showed spontaneous, LED-like emission, confirming device layers remain intact after mechanical liftoff.

Microstructure and mechanical properties of multilayer (TiB+TiB2+TiC)/Ti-6Al-4V composite in laser powder bed fusion additive manufacturing process

The paper presents the analysis of the physical and mechanical properties of the heterogeneous material based on the ceramics TiB, TiB2, TiC, B4C and metal alloy Ti-6Al-4V formed by the SLM method. The effect of ceramic particles TiB, TiB2, TiC, B4C resulting from in situ synthesis under the laser action on the microstructure and hardness of the formed metal-matrix composite has been studied. Under discussion are the main mechanisms of change of the microstructure with secondary ceramic insertions, the hardness is measured at the micro-level.

Development a Method for Estimating a Safe Distance between Coagulates to Automatically Plan Retinal Laser Coagulation in Diabetic Retinopathy Treatment

Introduction. Diabetes mellitus is a common endocrine disease that can lead to retinal vascular damage caused by the spread of macular edema and the development of diabetic retinopathy. Currently, diabetic retinopathy is treated using retinal laser coagulation. However, since even modern systems do not demonstrate sufficient treatment efficacy, methods for providing laser coagulation support on the basis of patient data analysis are required.Aim. This paper aims to develop and study a method for estimating a safe distance between coagulates via the mathematical modeling of coagulation in order to provide laser coagulation support.Materials and methods. The problem of thermal conductivity is numerically modeled for laser action in a multilayer medium.Results. A method for estimating a safe distance between coagulates has been developed via the mathematical modeling of the thermal conductivity problem. An algorithm was established for reconstructing a three-dimensional fundus structure from OCT images. It was demonstrated that the convergence rate of the integro-interpolation method is higher than that of the finite difference method. The study revealed that the retina heats up to 45 ºС due to heat redistribution from the epithelial layer, as well as laser exposure. According to the study results, the developed method yields a safe distance of 180 µm. By increasing the delay between laser pulses by more than 10 ms, this distance can be reduced to 160 μm.Conclusion. The developed method can calculate distance corresponding to that used in medical practice. Besides safe distance, the use of this method will allow other laser coagulation parameters to be determined non-invasively: laser power and pulse duration recommended to achieve a therapeutic effect. These estimates can be used to automatically produce a preliminary laser coagulation plan to support diabetic retinopathy treatment.

Prevention of The Development of Postoperative Complications and Their Treatment in The Surgery of Duedenal Purpose

The authors analyze various degrees of physiological anastomositis in 131 patients, and conclude that for the treatment of late anastomositis after surgical interventions on the stomach and duodenum, it is recommended to include the laser action of the anastomosis zone with two types of low-energy lasers in the complex program. The authors argue that the combined use of low-energy laser exposure through endoscopic and percutaneous irradiation will improve the effectiveness of the treatment of late anastomositis.

Expanding of Excimer Laser Photoablation’s Functionality in Ophthalmology

One of the significant weaknesses of excimer laser-based vision correction devices is the difficulty of achieving a required change in the refractive properties of the cornea to sharply focus the image on the retina with distance from the working area (ablation zone) center to the periphery due to a change in the laser beam incidence angle. The study is aimed at improving the quality of laser action on the eye cornea by introducing an optical corrective system into the existing excimer laser vision correction equipment, ensuring the coincidence of the direction of the laser beam incidence on the corneal surface with the normal.It has been shown that the greater the reflection coefficient, the lower the absorbed energy, and the shallower the laser radiation penetration and ablation depths, which reduces the laser action opportunities and quality. When using excimer laser vision correction devices, it has been proposed to change the angle of the laser beam incidence on the cornea with a distance from the working area (ablation zone) center to the periphery during the surgery by introducing an optical corrective system based on a lightweight controllable and movable mirror, which allows achieving the coincidence of the direction of the laser beam incidence on the corneal surface with the normal.The studies have shown that the coincidence of the laser beam incidence on the corneal surface at any point with the normal when using a priori data on the specifics of the patient's eye allows expanding the functional opportunities of excimer laser photoablation, i. e., expand the ablation zone by 30 % and eliminate the possibility of errors caused by the human factor. The technique proposed can be used for excimer laser vision correction according to PRK, LASIK, Femto-LASIK, and other methods. To implement this approach, a patented excimer laser vision correction unit has been proposed with a PCcontrolled optical shaping system comprising galvo motor platforms and galvo mirrors installed on them.

LIBS Monitoring and Analysis of Laser-Based Layered Controlled Paint Removal from Aircraft Skin

Reliability and controllability of selective removal of multiple paint layers from the surface of aircraft skin depend on effective online monitoring technology. An analysis was performed on the multi-pulse laser-induced breakdown spectroscopy (LIBS) on the surface of the aluminum alloy substrate, primer, and topcoat. Based on that, an exploration was conducted on the changes of the characteristic peaks corresponding to the characteristic elements that are contained in the topcoat, primer, and substrate with different layers of a laser action, in combination with analysis of microscopic morphology, composition, and depth of laser multi-pulse pits. The results show that the appearance and increase of the characteristic peak intensity of the Ca I at the wavelength of 422.7 nm can be regarded as the basis for the complete removal of the topcoat; the decrease or disappearance of the characteristic peak intensity can be regarded as the basis for the complete removal of the primer. Al I spectrum at the wavelength of 394.5 nm and 396.2 nm can be adopted to characterize the degree of damage to the aluminum alloy substrate. The feasibility and accuracy of the LIBS technology for the laser selective paint removal process and effect monitoring of aircraft skin were verified. Demonstrating that under the premise of not damaging the substrate, laser-based layered controlled paint removal (LLCPR) from aircraft skin can be achieved by monitoring the spectrum and composition change law of specified wavelength position corresponding tothe characteristic elements that are contained in the specific paint layer.