Adam Cenian

Use of optical skin phantoms for preclinical evaluation of laser efficiency for skin lesion therapy

Abstract. Skin lesions are commonly treated using laser heating. However, the introduction of new devices into clinical practice requires evaluation of their performance. This study presents the application of optical phantoms for assessment of a newly developed 975-nm pulsed diode laser system for dermatological purposes. Such phantoms closely mimic the absorption and scattering of real human skin (although not precisely in relation to thermal conductivity and capacitance); thus, they can be used as substitutes for human skin for approximate evaluation of laser heating efficiency in an almost real environment. Thermographic imaging was applied to measure the spatial and temporal temperature distributions on the surface of laser-irradiated phantoms. The study yielded results of heating with regard to phantom thickness and absorption, as well as laser settings. The methodology developed can be used in practice for preclinical evaluations of laser treatment for dermatology.

Improvement of self-regeneration of gas mixtures in a convection-cooled 1.2 kW laser

Degradation of gas mixtures and methods of its reduction in lasers were studied with reference to the DC-excited, transverse-flow CW laser of MLT 1200 type. The long-term output characteristics and their dependence on the mixtures composition determined in the experiment gave a hint concerning the thorough theoretical analysis of decomposition in laser mixtures. The observed optimal concentration of lies within the range and that of is about 2 - 3% for the laser under consideration. In the theoretical analyses of available data we focus our attention on the roles played by the gas pressure, the mixture composition and the growth of the afterglow region in the reduction of working gas degradation. The equilibrium conversion decreases with increasing gas pressure. A 50% reduction in is obtained when the pressure increases from 13.33 to 46.66 hPa. The observed optimal composition corresponds to low reactivity of the laser plasma with a small oxygen content. The optimal period for the laser gas mixture to reside in the afterglow region is larger by a factor of 1000 than the discharge residence time. The relatively small value of the equilibrium conversion in the MLT 1200 laser results from relatively high concentrations of atomic and electronically excited species. The formation of atomic oxygen is inhibited by reactions with electronically excited molecules, especially . Only very small concentrations of and , which are the most harmful reaction products, result according to our calculations for the MLT 1200 system.

Characterisation of CFRP surface contamination by laser induced fluorescence

The application of Carbon Fibre Reinforced Polymers (CFRP) in aeronautics has been increasing. The CFRP elements are joint using rivets and adhesive bonding. The reliability of the bonding limits the use of adhesive bonding for primary aircraft structures, therefore it is important to assess the bond quality. The performance of adhesive bonds depends on the physico-chemical properties of the adhered surfaces. This research is focused on characterization of surfaces before bonding. In-situ examination of large surface materials, determine the group of methods that are preferred. The analytical methods should be non-destructive, enabling large surface analysis in relatively short time. In this work a spectroscopic method was tested that can be potentially applied for surface analysis. Four cases of surface condition were investigated that can be encountered either in the manufacturing process or during aircraft service. The first case is related to contamination of CFRP surface with hydraulic fluid. This fluid reacts with water forming a phosphoric acid that can etch the CFRP. Second considered case was related to silicone-based release agent contamination. These agents are used during the moulding process of composite panels. Third case involved moisture content in CFRP. Moisture content lowers the adhesion quality and leads to reduced performance of CFRP resulting in reduced performance of the adhesive bond. The last case concentrated on heat damage of CFRP. It was shown that laser induced fluorescence method can be useful for non-destructive evaluation of CFRP surface and some of the investigated contaminants can be easily detected.

Application of the laser diode with central wavelength 975 nm for the therapy of neurofibroma and hemangiomas

This paper presents a newly developed dermatological laser (with a central wavelength 975 nm) for application in therapies requiring deep penetration of tissue, e.g., cutaneous (dermal) neurofibroma (von Recklinghausen disease) and hemangiomas. This laser can work either in pulses or continues wave mode. Laser radiation is transmitted toward the application region by optical fiber with a diameter of 0.6 mm. The compact design of the laser facilitates its transport and increases the comfort of use.

Dissociation and heterogeneous recombination of CO molecules in sealed-off discharge plasmas contained in tubes of various materials

The paper presents results of experimental and numerical investigations of sealed-off discharge plasmas containing CO molecules, generated in molybdenum glass, fused alumina ceramics or Pyrex tubes. The rates of heterogeneous recombination on Pyrex and fused alumina surfaces were estimated. The determined probabilities of recombination on fused-alumina surface are significantly greater than on molybdenum glass or Pyrex. This results in significantly smaller CO dissociation-level in fused alumina discharge-tube than in glass one.

Heterogeneous vibrational relaxation of carbon monoxide

The first results relating to heterogeneous vibrational relaxation of carbon monoxide in an Al2O3 ceramics tube are reported, together with an estimation of its probability. It was found that the probability of heterogeneous relaxation εv of the first-excited state of CO on the Al2O3 surface lies in the range (5 to 7) × 10(-2). The measurements show that the probabilities of heterogeneous relaxation of CO(X(1)Σ, v) do not depend on the value of v, at least for v = 1, 2 and 3.

Influence of laser modification of TiO2 films for its photocatalytic properties

The photocatalytic activity of TiO2 layer modified by laser radiation is discussed in the paper. Commercially available nanopowder P25(Degussa) was used, which consists of a mixture of anatase and rutile - two crystallographic forms of TiO2 . The spin-coating technique was applied to produce thin layers on glass. After drying and calcination the layer was thermally modified using a pulsed (6 ns) Nd:YAG laser (FHG 266 nm). This caused a clearly visible surface darkening effect. The XRD spectra show that phase change transition (from anatase to rutile) took place partially. This was also confirmed by Raman spectra. The main peak of Raman-spectra shifts from 142,84 to 145,22 cm-1, probably due to decreasing size of TiO2 nanoparticles or more probably due to a defects generation in nanocrystallite structure. Defects have been reported in the literature as surface oxygen depletion and generation valance states Ti3+ and Ti4+. Eventually, kinetics of methylene-blue decay and CO2 to methane conversion were examined. In both cases an increase of catalytic activity was observed.

Plume investigations of the mechanisms of SiO laser ablation at 266 nm

The ablation mechanism of SiO at the laser wavelength of 266 nm has been investigated by characterizing the composition and dynamics of neutral and charged particles produced in the ablation. The neutral and ionized composition of the plume and the dynamics of neutral SiO were investigated by time-of-flight mass spectrometry. The velocity distribution of neutral SiO molecules shows contributions of slow and fast components. The velocity distributions of charged species in the plume were investigated by a Langmuir probe technique, obtaining that the distributions shift towards higher velocities with increasing distance from the target surface. The fastest component of the velocity distribution of neutral SiO overlaps the slowest part of the velocity distribution of charged species. The average rotational energy of SiO molecules, estimated by LIF spectroscopy does not allow to draw clear conclusions about the participation of silicon oxide ion clusters as the precursors of fast SiO molecules in the plume.

Langmuir probe diagnostics of plasma generated by means of pulsed Nd:YAG laser interaction with Si-based targets

Investigations of laser ablation plume aimed at applications for the SiO nano-film deposition are reported. The plasma formation and propagation through experimental chamber was investigated by means of Langmuir probe. The effects related to plume splitting and acceleration are discussed.

Investigations of the influence of working mixture composition on a CO2 laser performance

Some results of plasma-chemical modeling of CO2 laser discharges are presented in this paper. The influence of various mixture components and products of chemical processes on the CO2 laser operation-parameters is discussed. The crucial role of electronic excited species was proved. The calculated values of N2O concentration in different laser mixtures were close to the ones measured by a FTIR spectroscope.