Paweł E. Kozioł

Laser prototyping of printed circuit boards

This paper describes the application of laser micromachining to rapid prototyping of printed circuit boards (PCB) using nano-second lasers: the solid-state Nd:YAG (532/1064 nm) laser and the Yb:glass fiber laser (1060 nm). Our investigations included tests for various mask types (synthetic lacquer, light-sensitive emulsion and tin). The purpose of these tests was to determine some of the basic parameters such as the resolution of PCB prototyping, speed of processing and quality of PCB mapping with commonly available laser systems. Optimization of process parameters and the proposed conversion algorithm have allowed us to produce circuit boards with a resolution similar to that of the Laser Direct Imaging (LDI) technology.

Laser Doppler vibrometry with a single-frequency microchip green laser

We have developed a laser vibrometer based on an Nd:YVO4/YVO4/KTP monolithic single-frequency green laser operating at 532 nm, with a narrow linewidth of radiation. Two configurations of the laser Doppler vibrometer have been investigated—with the so-called single- and double-frequency Bragg shifts. Measurement of heterodyne signals as a mixing result of scattered and reference beams has been carried out. In both configurations we have obtained signals with a high S/N ratio of >30 dB with resolution bandwidth = 200 kHz for a vibrometer output power of 3 mW. In our opinion, stable single-frequency solid-state green lasers provide new opportunities for the development of miniature laser vibrometry.

Excimer laser-induced incubation of poly(L-lactide)

The irradiation of polylactide by KrF excimer laser with subthreshold fluence results in modification of its properties via photochemical reactions. A common approach is to modify chemical composition of polymer surface by UV irradiation, for example, in order to improve their wetting properties. In this paper, authors present a possibility of bulk modification of poly(L-lactide) which is related to photofragmentation and creation of new terminal groups. The irradiation results in decrease of molecular weight and increase of polydispersity. The appearance of new terminal groups is responsible for enhancement of absorption in UV-C range. The intensity of chemical composition changes introduced by UV irradiation can be precisely dosed thanks to a pulse character of laser source. Modifications can be controlled during the process by the analysis of energy transmitted through a polymer sheet. The distribution of absorption coefficient changes along with the depth of irradiated polymer and its correlation with polydispersity was discussed. Presented technique can be used for selective and controllable modification of hydrolytic degradation time of biodegradable polyesters utilized in biomedical applications.

Fabrication of Fresnel microlens with excimer laser contour ablation

Laser micromachining systems based on excimer lasers are usually oriented to work with mask projection regime because of the low pulse repetition rate as well as large beam aperture of the laser source. In case of fabricating of the complex 3D structures, this approach introduces a number of limitations. Alternative solution might be usage of direct writing laser mode. Some examples of the so called contour ablation approach for fabricating microlenses with an absolutely monotonically changing cross-sectional profile are presented in the literature. Based on this idea and introducing new variables like automatic mask selection as well as optimizing process algorithms led us to obtain more versatile method for shape approximation. Hence, there were fabricated structures with cross-sectional profiles described as functions that are monotonic on specified intervals such as Fresnel microlenses. In this paper we describe approximation of process parameters for obtaining desired cross-sectional profiles and finally fabrication of few exemplary microlenses. All structures were characterized by a digital optical microscopy and compared to the given profiles. The accuracy of reproduction of the desired structures at the level of single microns was achieved.

Effect of CO2 laser micromachining on physicochemical properties of poly(L-lactide)

In this paper, we present some examples of micromachining of poly(L-lactide) with a CO2 laser and an analysis of changes in material properties in the heat affected HAZ induced by the fluence well above the ablation threshold. The complexity of the processes of decomposition implies the need for simultaneous use of many selective analytical techniques which complement each other to give a full image of the changes. Introduced changes were characterized using Differential Scanning Calorimetry (DSC), Gel Permeation Chromatography (GPC), X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR). It turns out that CO2 laser processing of poly(L-lactide) mainly induces surface changes. However, oxidation of the surface was not observed. We recorded a bimodal distribution and some reduction in the molecular weight. Infrared spectroscopy in turn revealed the existence of absorption bands, characteristic for the vinyl groups (RCH=CH2). The appearance of these bands indicates that the decomposition of the polymer occurred, among others, by means of the cis-elimination reaction.

Direct selective metallization of AlN ceramics induced by laser radiation

Aluminum nitride (AlN) ceramics has a unique characteristic, namely the ability to form conductive structures on its surface directly by laser-induced decomposition of the base material. Various research has been carried out on obtaining low-ohmic structures depending on process parameters such as the laser power, overlap of subsequent pulses and the type of shielding gas (air, nitrogen and argon). This paper focuses on explaining which factors have the greatest impact on the resistance (resistivity) value of obtained structures. In order to explain the effect of the laser fluence (below and above the ablation threshold of aluminum nitride) on the chemical structure of the conductive layers, qualitative EDX analyses were performed. Optimization of the process allowed obtaining a resistivity of the conductive layers at a level of ρ = 0.64·10-6 Ω·m, with a thickness of aluminum up to 10 μm (sheet resistance RS = 10 mΩ/Sr). This technology can be useful in making printed circuit boards (PCB), various types of sensors as well as radio-frequency identification (RFID) and Lab-On-a-Chip (LOC) structures. This technology can also be useful for the production of metamaterials.

Resonator structures on AlN ceramics surface treated by laser radiation

In this paper a method for producing resonant structures using laser micromachining is presented. In the spot of laser beam impact on AlN ceramics surface a conductive aluminum layer is formed. Compilation of process parameters allows for the fabrication of structures with resistance at Rs ~ 0.01Ω/Rs. It has been also found out that the maximum value of resistance for which spiral resonator structures manifest their unique properties is at the level of Rs = 1.43 Ω. Furthermore, the occurrence of mutual capacity which value is dependent on the arrangement of individual SR structures with respect to each other was observed and examined. Based on satisfactory results for SR structures, it has been attempted to produce a resonant structures dedicated to the THz range based on the process of direct metallization of AlN ceramics surface. As a result, the Split Ring Resonator structure whose properties were verified by using the THz -TDS method was manufactured. In case of the field E perpendicular to SRR structure and one resonance area for 0.50 THz with field E parallel to the structure, two characteristic resonant dips for 0.22 THz and 0.46 THz were obtained. The studies confirmed that the method of direct metallization of AlN ceramics allows to produce resonant structures in the THz range.

Spiral resonator manufactured on AlN ceramics to filter the coupled wave between patch antennas

The objective of this paper was to present an alternative technique of manufacturing the unit cells of spiral-shaped resonators (SR) on the aluminium nitride (AlN) ceramics. In this technique the AlN plane surface is irradiated by the Yb:glass medium-power laser (1.06 µm). As a result of the irradiation by a focused laser beam (a laser beam power up to 20 W), the rupture of the aluminium and nitrogen physical bonds occurs. Under such circumstances the conductive aluminium “paths” are formed on the originally insulating ceramic surface. Upon obtaining low ohmic conductive paths, this method makes for the feasible manufacturing of metamaterial structures. In carried out studies, the usage of such structures to suppress the coupling between pairs of patch antennas has been examined. The improvement of the mutual coupling at the level of 10 dB has been obtained. One of the advantages of the demonstrated method is a possibility to perform the selective and direct metallization of the AlN ceramics surface without using any mask as opposed to photolithography. It greatly reduces the implementation time of the projected metamaterial structures.

Laser-induced color marking of stainless steel

This paper presents the analysis of the impact of selected process parameters on the resulting laser color marking. The study was conducted for AISI 304 multipurpose stainless steel using a commercially available industrial fiber laser. It was determined how various process parameters, such as laser power, scanning speed of the laser beam, temperature of the material, location of the sample relative to the focal plane, affect the repeatability of the colors obtained. For objective assessment of color changes, an optical spectrometer and the CIE color difference parameter ΔEab * were used.

Experimental verification of the method for producing a three-dimensional cross-pairs metamaterial structure based on a dielectric AlN cube

This paper presents a method of manufacturing 3D metamaterial structures using laser radiation. Our proposed material, aluminum nitride (AlN), by interaction of a high-energy laser beam undergoes a direct metallization process, a result of which a conductive aluminum layer is formed on the ceramic surface at the spot of the laser radiation. Using this unique feature on all six sides of an AlN ceramic cube, the designed cross-pairs were mapped. Unit cells were exposed to an electromagnetic wave, by which the occurrence of the resonant areas of reflectance and transmittance for 7.27 GHz and 9.14 GHz was observed. To demonstrate the property of the negative refractive index a prism made out of manufactured cubes was created. For a wave propagating through a wedge-shaped prism for certain frequency bands, a negative refraction angle was observed.