450 nm (Al,In)GaN optical amplifier with double 'j-shape' waveguide for master oscillator power amplifier systems.

In this paper we demonstrate 450 nm (Al,In)GaN graded index separate confinement heterostructure travelling wave optical amplifier with a double 'j-shape' waveguide. The length of the amplifier is 2.5 mm and the width of the ridge is 2.5 µm. The active region consists of three 3.5 nm thick quantum wells. The measured optical gain under CW operation in room temperature exceeded 29 dB for low power input signals. The saturation output power was 21 dBm for 400 mA driving current. The demonstrated amplifier, provides a good solution for the blue light, all nitrides, and master oscillator power amplifier systems.

3D Printing in the Fight Against Covid-19.

Purpose: The paper describes the design concept and findings from technological and initial clinical trials conducted to develop a helmet for non-invasive oxygen therapy using positive pressure, known as hCPAP (Helmet Continuous Positive Airway Pressure). Methods: The study utilized PET-G filament, a recommended material for medical applications, along with the FFF 3D printing technique. Additional technological investigations were performed for the production of fitting components. The authors proposed a parameter identification method for 3D printing, which reduced the time and cost of the study while ensuring high mechanical strength and quality of the manufactured elements. Results: The proposed 3D printing technique facilitated the rapid development of an ad hoc hCPAP device, which was utilized in preclinical testing and treatment of Covid-19 patients, and yielded positive results. Based on the promising outcomes of the preliminary tests, further development of the hCPAP device's current version was pursued. Conclusion: The proposed approach offered a crucial benefit by significantly reducing the time and costs involved in developing customized solutions to aid in the fight against the Covid-19 pandemic.

Fabrication of phase masks with variable diffraction efficiency using HEBS glass technology.

A new fabrication method of apodized diffractive optical elements is proposed. It relies on using high energy beam sensitive glass as a halftone mask for variable diffraction efficiency phase masks generation in a resist layer. The presented technology is especially effective in mass production. Although fabrication of an amplitude mask is required, it is then repeatedly used in a single shot projection photolithography, which is much simpler and less laborious than the direct variable-dose pattern writing. Three prototypes of apodized phase masks were manufactured and characterized. The main advantages as well as limitations of the proposed technology are discussed.

Deformation Process of 3D Printed Structures Made from Flexible Material with Different Values of Relative Density.

The main aim of this article is the analysis of the deformation process of regular cell structures under quasi-static load conditions. The methodology used in the presented investigations included a manufacturability study, strength tests of the base material as well as experimental and numerical compression tests of developed regular cellular structures. A regular honeycomb and four variants with gradually changing topologies of different relative density values have been successfully designed and produced in the TPU-Polyflex flexible thermoplastic polyurethane material using the Fused Filament Fabrication (FFF) 3D printing technique. Based on the results of performed technological studies, the most productive and accurate 3D printing parameters for the thermoplastic polyurethane filament were defined. It has been found that the 3D printed Polyflex material is characterised by a very high flexibility (elongation up to 380%) and a non-linear stress-strain relationship. A detailed analysis of the compression process of the structure specimens revealed that buckling and bending were the main mechanisms responsible for the deformation of developed structures. The Finite Element (FE) method and Ls Dyna software were used to conduct computer simulations reflecting the mechanical response of the structural specimens subjected to a quasi-static compression load. The hyperelastic properties of the TPU material were described with the Simplified Rubber Material (SRM) constitutive model. The proposed FE models, as well as assumed initial boundary conditions, were successfully validated. The results obtained from computer simulations agreed well with the data from the experimental compression tests. A linear relationship was found between the relative density and the maximum strain energy value.

Static and Dynamic Loading Behavior of Ti6Al4V Honeycomb Structures Manufactured by Laser Engineered Net Shaping (LENSTM) Technology.

Laser Engineered Net Shaping (LENSTM) is currently a promising and developing technique. It allows for shortening the time between the design stage and the manufacturing process. LENS is an alternative to classic metal manufacturing methods, such as casting and plastic working. Moreover, it enables the production of finished spatial structures using different types of metallic powders as starting materials. Using this technology, thin-walled honeycomb structures with four different cell sizes were obtained. The technological parameters of the manufacturing process were selected experimentally, and the initial powder was a spherical Ti6Al4V powder with a particle size of 45-105 µm. The dimensions of the specimens were approximately 40 × 40 × 10 mm, and the wall thickness was approximately 0.7 mm. The geometrical quality and the surface roughness of the manufactured structures were investigated. Due to the high cooling rates occurring during the LENS process, the microstructure for this alloy consists only of the martensitic α' phase. In order to increase the mechanical parameters, it was necessary to apply post processing heat treatment leading to the creation of a two-phase α + ß structure. The main aim of this investigation was to study the energy absorption of additively manufactured regular cellular structures with a honeycomb topology under static and dynamic loading conditions.

Indium Incorporation into InGaN Quantum Wells Grown on GaN Narrow Stripes.

InGaN quantum wells were grown using metalorganic chemical vapor phase epitaxy (vertical and horizontal types of reactors) on stripes made on GaN substrate. The stripe width was 5, 10, 20, 50, and 100 µm and their height was 4 and 1 µm. InGaN wells grown on stripes made in the direction perpendicular to the off-cut had a rough morphology and, therefore, this azimuth of stripes was not further explored. InGaN wells grown on the stripes made in the direction parallel to the GaN substrate off-cut had a step-flow-like morphology. For these samples (grown at low temperatures), we found out that the InGaN growth rate was higher for the narrower stripes. The higher growth rate induces a higher indium incorporation and a longer wavelength emission in photoluminescence measurements. This phenomenon is very clear for the 4 µm high stripes and less pronounced for the shallower 1 µm high stripes. The dependence of the emission wavelength on the stripe width paves a way to multicolor emitters.