The bleaching of polyacrylamide tattooed skin-mimicking phantoms by a series of laser pulses in a single session is studied. It is shown that compared to the single-pulse procedures tattoo removal by series of laser pulses allows not only for reducing the necessary laser fluence, but also for improving the degree of bleaching. The dynamics of formation and dissolution of microscopic gas bubbles in tattooed skin phantoms exposed to laser radiation is also studied. A laser-induced tattoo bleaching mechanism is suggested, based on the process of selective photo-thermolysis of pigmented particles in conditions where the thermal conductivity of the medium surrounding the particles is decreased because of the microbubbles formed therein.
Light field intensity distribution in three-dimensional polylactide scaffolds after irradiation with low-intensity light from one side of the samples has been determined in the visible and near-infrared regions of the spectrum. Two different types of scaffolds manufactured by the methods of supercritical fluid foaming and surface selective laser sintering have been investigated. The problem is solved by numerical calculation according to the Monte Carlo method involving experimentally obtained information about effective optical parameters of the scaffold material. Information about intensity distribution of the incident light in the matrix volume is needed to assess the radiation level for the scaffold cells after photobiostimulation. It has been shown that the formation of the light field in case of strongly scattering media, such as polylactide scaffolds, is determined by anisotropy g and the scattering coefficient μs.
We have elaborated substrates for surface enhanced Raman scattering (SERS) based on carbon nanowalls (CNW) deposited with Ag nanoparticles and thin Ag films. For carbon nanowalls deposited with silver nanoparticles, the achieved analytical enhancement factor SERS was from 50 to 2500. Much higher analytical enhancement factor of SERS, up to 5×104, was obtained for carbon nanowalls deposited with thin Ag film. In this case the SERS signal is determined by fractal structure of carbon nanowalls covered by Ag films. Such fractal structure provides a strong inhomogeneous localization of light, formation of a large number of hot spots and leads as a result to significant enhancement of SERS signal.
In present paper we describe the development of advanced laser stereolithography (LS) methodology based on
photopolymerisation of a new liquid mixture of polyfunctional acrylic monomers and osteoinductive hydroxyapatite
powder. Supercritical carbon dioxide treatment of LS samples introduced both surface and bulk microporosity for
enhanced primary cell attachment and to remove toxic additives improving biocompatibility of the materials. The results
of in vitro tests comprising human osteoblast cells attachment, spreading and proliferation on the implants demonstrate
low level of their cytotoxicity and high level of biocompatibility. We also present a novel Surface Selective Laser
Sintering (SSLS) technique for biodegradable polymer scaffolds fabrication from thermosensitive poly(D,L-lactic) - and
poly(D,L-lactic-co-glycolic) acids - polymers, which have a wide spread occurrence in biomedical applications. Unlike
conventional Selective Laser Sintering (where the powder particles melt because of their volumetric absorption of the
laser radiation), in SSLS initiation of the sintering occur due to near IR laser beam absorption by a small amount
(<0.1wt.%) of biocompatible carbon black microparticles uniformly distributed along the polymer powder surface. This
technique enable to prevent any significant changes in polymer initial structures and even incorporate bioactive enzymes
into the samples. The results of our in vitro studies using 3T3 fibroblast, C2C12 myoblast and ovine meniscal
chondrocyte cells cultures hold great promise for use of produced scaffolds and developed technique in tissue
engineering.
The optical properties of emulsion nanocomposite materials based on powder silicon are studied. The method of creation of a new type of emulsion composite, allowing the control of the spectral structure of transmitted electromagnetic radiation is reported. Two series of powder silicon, containing SiOx (type 1) and SiOx + SiNx (type 2) depending on conditions were obtained and investigated. The results of FTIR-spectroscopy of powder silicon claimed the formation of SiO2 and SiOx phases on the surface layer of sample type 1 and the formation of nitride phase on the surface layer of sample type 2. The Raman Spectroscopy investigation of two series samples allowed to appreciate the dimensions of nanoparticles and phase structure in powder silicon. The Raman Spectra of samples type 1 and type 2 at the region of 500-600 cm-1 demonstrated that our powder silicon is nanocristalline silicon with dimension of d=10±2 nm for type 1 and d=13±2 nm for type 2. We prepared emulsion composite samples with nanocristalline silicon; the test run of these materials was performed. The Spectra of optical density as well as the spectra of transmission and diffusive reflection into integrative sphere were measured for both types of samples. It was shown that the samples of type 2 are preferable as main protective ingredients of sunscreens.
The results of an experimental study of the possibilities of monitoring erbium yttrium aluminum garnet laser-mediated ablation of human epidermis with the use of Fourier transform infrared (FTIR) spectroscopy and spectral polarization techniques are presented. The attenuated total reflection (ATR) method was used for FTIR spectroscopic measurements. Spectral polarization monitoring of the ablation was carried out by analyzing the spectra of the degree of residual linear polarization of a probe light diffusely reflected from the laser-treated region of skin. It was found that the analysis of FTIR spectra allows monitoring of the water and protein contents in the subsurface layers of the treated skin, while the degree of residual polarization measured at the wavelengths of maximal absorption of hemoglobin is sensitive to changes in the epidermis thickness and the blood content in the dermal layer (the degree of erythema).
Kinetics of water diffusion in laser-irradiated cartilage and cornea was studied. Optical polarization analysis was applied for visualizing of aqueous solution diffused through laser-irradiated biological tissues. Diffusion coefficients of different physiological solutions in cartilage and cornea were measured.
Studies of UV laser photolysis of Er organometallics (ErFOD) impregnated into porous Vycor glass in supercritical CO2 was performed, aimed at developing a new approach to glass microstructuring. It was revealed that quantum yield of UV laser photolysis increases with laser intensity. Efficiency of ErFOD photodegradation for the XeCl laser irradiation is almost two orders of magnitude higher than that for KrF laser. The effect of light scattering in the porous glass on the focusing of laser beam was also revealed.
The temperature alterations in the absorption coefficients of water in cartilage and cornea under laser radiation of an IR Free Electron Laser (FEL) were studied for several wavelengths near 2.9 and 6.1 μm water absorption bands using a pulsed photo-thermal radiometer (PPTR). A computation algorithm has been modified to take into account the real IR absorption spectra of the tissue and the spectral sensitivity of the IR detector used. The IR absorption spectra of cartilage and cornea have been also measured by the FTIR spectrometer. It is shown that the values of absorption obtained ising PPTR differ from that obtained by the spectrometer. The limitation and possible errors of two techniques used for have been discussed.
The possibility of efficient modification of nanoporous glasses by supercritical fluid (SCF) impregnation of erbium and copper organometallics to pores and subsequent thermal annealing of glass is shown. Experiments demonstrate unambiguously the advantage of SCF impregnation approach over liquid impregnation -- much higher rate of impregnation and absence of residual solvents: supercritical fluid -- sc-CO2-releases through pores. It was shown by monitoring Stark structure of Er3+ absorption bands and ESR spectra of CU2+ in glasses impregnated with Er and Cu organometallics that erbium and copper randomly built in network of glass. The maximal concentrations of Er3+ in nanoporous glass after SCF impregnation and subsequent annealing were estimated: 6x1020 cm-3 and 2x1020 cm-3 accordingly.
The formation of radicals upon UV and IR laser irradiation of some biological tissues and their components was studied by the EPR technique. The radical decay kinetics in body tissue specimens after their irradiation with UV light were described by various models. By the spin trapping technique, it was shown that radicals were not produced during IR laser irradiation of cartilaginous tissue. A change in optical absorption spectra and the dynamics of optical density of cartilaginous tissue, fish scale, and a collagen film under exposure to laser radiation in an air, oxygen, and nitrogen atmosphere was studied.
We developed a new surgical procedure to correct cartilaginous deformities of the nasal septum using transmucosal laser irradiation without the need for sedation or traditional septoplasty techniques in particular the creation of mucoperichondrial flaps. Since 1988, at the Sechenov Medical Academy of Moscow, 150 patients have underwent laser septal cartilage reshaping using a Holmium:YAG laser. Minimal re-relaxation of shaped septa was observed. Rhinomanometric findings confirmed subjective assessments of improved breathing and relief of nasal obstruction. Laser septoplasty involves photothermal non-destructive heating of the septal cartilage allowing plastic deformation of this tissue. It is performed in an outpatient setting requiring only about ten minutes to complete without the need for sedation or splints. No visible undesirable side effects were observed for all patients underwent to laser reshaping procedure. It is shown that the laser reshaping is a simple bloodless, painless procedure. Potential applications in aesthetic, reconstructive, and pediatric head and neck surgery are discussed.
Optical properties of carbon dioxide in the vicinity of its critical point were studied. Amplitude-frequency characteristics of radiation backscattered in CO2 have been studied using laser Doppler velocimeter based on highly stabilized Nd:YAG3+ chip-laser. Significant (up to 10 times) narrowing of backscattered radiation spectrum and increasing of its amplitude (up to 100 times) in the vicinity of critical point were detected and analyzed. Nonlinear temperature dependence of reflection from glass- CO2 interface was observed. Intrinsic anomaly of light reflection of critical media was revealed. Transmission spectrum of cell with critical CO2 was measured in 0.35- 1 micrometers spectral range. Formula for integral spectrum of light scattered in near-critical medium was obtained.
We have measured differential spectra of water in thin films of Chondroitine sulfate and collagen. After we have calculated a relative quantity of tightly bound water in samples. Percentage of bond water molecules is higher in biopolymer films than in bulk water. It is probably due to formation of water bridges which stabilize the polymer structure.
In this work we have used for the first time 1.56 micrometer fiber laser to study mechanisms of IR laser induced stress relaxation in cartilage. We have applied several in-situ monitoring techniques: local temperature measurements (IR radiometry and thermocouple), IR-light absorption, direct stress measurements, micro-balancing, visible light scattering and optical coherent tomography. We have measured temporal behavior of 1.56 micrometer laser light transmission through the cartilage sample at different intensities with synchronous temperature and stress monitoring. The observed bleaching effect (self-induced transparency) is caused by water release from irradiating zone, water evaporation from the cartilage surface and, also, by temperature shift and decrease of intensity of water absorption bands.
Clinical results on sparing laser reshaping of nasal septum cartilage are reported for the first time. Forty patients have been treated with holmium laser to correct a deformed cartilage. The laser reshaping is a bloodless, painless procedure which takes few minutes to straighten nasal septum. The stability of the new shape and possible side effects have been examined during twelve months. The headache and other negative symptoms have disappeared, as a result of laser treatment for the most of patients. Rhinoscopic examination show an excellent long-term reshaping effects for nasal septum of 23 patients, and, also, good results for other 12 patients. For 5 patients only a little effect takes place. Our rhinomanometric examinations demonstrate a pronounced improvement of the breathing for 35 patients. No visible undesirable side effects were observed for all patients underwent to laser reshaping procedure.
The results of recent study of cartilage reshaping in vivo are reported. The ear cartilage of piglets of 8-12 weeks old have been reshaped in vivo using the radiation of a holmium laser. The stability of the shape and possible side effects have been examined during four months. Histological investigation shown that the healing of irradiated are could accompany by the regeneration of ear cartilage. Finally, elastic type cartilage has been transformed into fibrous cartilage or cartilage of hyaline type.
The aim of this work is to control shaping of cartilage under laser heating with acoustic and opto-acoustic approaches. Generation of acoustic signal in cartilage is due to water movement through porous cartilage matrix.
Evgueni Antonov, Victor Bagratashvili, Vladimir Popov, Emil Sobol, Steven Howdle, Christine Joiner, Kate Parker, Terry Parker, Alexander Doktorov, Valeri Likhanov, Alexander Volozhin, Sergey Alimpiev, Sergey Nikiforov
Optical parameters (scattering coefficient s, absorption coefficient k and scattering anisotropy coefficient g) of hyaline cartilage were studied for the first time. Optical properties of human and pig nasal septum cartilage, and of bovine ear cartilage were examined using a spectrophotometer with an integrating sphere, and an Optical Multi-Channel Analyser. We measured total transmission Tt, total reflection Rt, and on-axis transmission Ta for light propagating through cartilage sample, over the visible spectral range (14000 - 28000 cm-1). It is shown that transmission and reflection spectra of human, pig and bovine cartilage are rather similar. It allows us to conclude that the pig cartilage can be used for in-vivo studies instead of human cartilage. The data obtained were treated by means of the one-dimensional diffusion approximation solution of the optical transport equation. We have found scattering coefficient s, absorption coefficient k and scattering anisotropy coefficient g by the iterative comparison of measured and calculated Tt, Rt and Ta values for human and pig cartilage. We found, in particular, that for 500 nm irradiation s equals 37,6 plus or minus 3.5 cm-1, g equals 0,56 plus or minus 0.05, k approximately equals 0,5 plus or minus 0.3 cm-1. The above data were used in Monte Carlo simulation for spatial intensity profile of light scattered by a cartilage sample. The computed profile was very similar to the profile measured using an Optical Multi-Channel Analyzer (OMA).
The paper presents theoretical and experimental results allowing to discuss and understand the mechanism of stress relaxation and reshaping of cartilage under laser radiation. A carbon dioxide and a Holmium laser was used for treatment of rabbits and human cartilage. We measured temperature, stress, amplitude of oscillation by free and forced vibration, internal friction, and light scattering in the course of laser irradiation. Using experimental data and theoretical modeling of heat and mass transfer in cartilaginous tissue we estimated the values of transformation heat, diffusion coefficients and energy activation for water movement.
The dynamics of light scattering and internal force in cartilage in vitro are studied in the course of laser shaping. In experiments were used the samples of human cartilage which were collected from patients who underwent nasal septum stirgely. We found that the dynamic of scattered light intensity depends on heating rate and on the temperature of the sample. The sign of the derivative of the scattered light intensity changes when phase transition is occur. The stress force changes during laser heating and relax after action to much less value than it was before laser treatment. Histological investigation allow us to correlate the dynamics of optical and mechanical properties of cartilage with stable and nondestructive reshaping regimes.
The problem of a purposeful change of the shape of cartilage is of great importance for otolaryngology, orthopaedics, and plastic surgery. In 1992 we have found a possibility of controlled shaping of cartilage under moderate laser heating. This paper presents new results in studies of that phenomenon. We have measured temperature and stress in a tissue undergoing to irradiation with a Holmium laser. Study of cartilage structure allowed us to find conditions for laser shaping without pronounced alterations in the structure of matrix.
We examine thermal effect of a 2.1 micrometer Holmium laser on the internal stress and shape of cartilage. For 2.1 microns radiation, the absorption depth is more by an order of magnitude than that, for 10 micrometer radiation. We have studied the influence of laser intensity, pulse duration, pulse repetition rate, and of cartilage thickness on its shaping conditions. Spatial and temporal locality of Ho laser radiation as well as the bulk character of the heating allow us to produce the stress relaxation without overheating of the surface irradiated and to prevent undesirable effects of tissue carbonization and destruction.
We have established that the phenomenon of cartilage shaping under the laser irradiation is connected with the bound-to-free transformation of water at a temperature around 70 degrees Celsius. The process of laser-induced stress relaxation in cartilage is accompanied and may be detected by the (1) mechanical, (2) thermal, and (3) optical effects. No pronounced structure effects were observed, for optimal conditions of the laser shaping of cartilage. The significance for otolaryngology of new laser applications for the shaping of cartilage is discussed.
The carbon dioxide laser has been used for the first time to change the cartilage's shape. After the laser irradiation the cartilage has the tendency to retain its new form. Different types of laser modified cartilage structures were studied. The inferred physical mechanism for cartilage shaping using the stresses relaxation process is presented. The clinical significance of the results for corrective laser surgery is discussed.
Pre-ablative processes and destruction mechanisms of tissues under laser radiation are considered. It is shown that diffusion-limited processes of drying and carbonization may have a dramatic effect on the absorption and heating kinetics and on the change of laser ablation mechanisms. The manifestation conditions, advantages and disadvantages of various ablation mechanisms are discussed.
The possibilities and advantages of UV-laser ablation technique for deposition of doped PbTe thin films are discussed. To understand the effects of experimental parameters on layer formation the stages of laser sputtering of the target and film growth were investigated. Method of laser ionization RETOF mass spectrometry was used to obtain the energy distribution and chemical nature of evaporated particles as a function of wavelength and laser radiation power. The influence of experimental parameters on the deposited film thickness, stoichiometry and crystalline perfection was checked. The dependence of doped PbTe films photoelectrical properties on the experimental parameters.
In this work, we investigate the velocity distribution function of neutral yttrium atoms which appeared during the laser evaporation of different targets (pure metallic yttrium, yttrium oxide Y2O3, and high Tc ceramics YBa2Cu3O7-x). We also investigate the influence of buffer gas and external electric field on the distribution function.
The mechanisms of UV induced decomposition of oxygen-deficient centers (ODC) in silica glass has been experimentally studied. It is shown that high intensity irradiation of silica glass results in the two-step decomposition of ODC and formation of paramagnetic E' centers. At the same time at low UV irradiation intensity (laser, mercury lamp) the single quantum reaction of ODC with gas-phase impurities in the net of silica is the dominant process of ODC photoreaction.
By picosecond spectrometer with two tunable dye lasers, high temperature superconducting (HTSC) (monocrystal Y-Ba-Cu-O with critical temperature Tc equals 87 K) and metal (Ni) thin films have been investigated. A self-diffraction process efficiency (eta) versus biharmonic pumping component detuning (Omega) has been measured at the temperature (Theta) equals 300 and 80 K. It is found that there is a well-defined dip on the dispersion curve (eta) ((Omega) ) for the HTSC films at (Theta) equals 80 K and -10 cm-1 (Omega) -50 cm-1. This region upper limit corresponds to a superconducting energy gap value 2(Delta) . At 10 cm-1 -1, any distinction of the same type is absent. In other respects all obtained dispersion curves are similar. They consist of the central peak ((eta) approximately equals 10-7, (Omega) -1) and wide wings ((eta) approximately equals 10-9, (Omega) 10 cm-1) with the interference structure. Y-Ba-Cu-O film resonances are coincided with the phonon mode frequencies (120, 335, and 580 cm equals -1). It is shown that photoexcitation kinetics (the sample ''darkening'') must consist of some components. A characteristic time of the most ''ultrafast'' component below 5 fs has been estimated and a complex subpicosecond quantum beats presence has been predicted.
The action of powerful laser radiation on superconducting materials is very important for different applications. Laser ablation was successfully used for the deposition of thin superconducting films, and for thin film patterning. Laser modification of thin superconducting films without any ablation of material has been also
demonstrated. This work presents the results of our experimental and theoretical studies of the laser induced decomposition, evaporation, and ablation processes in 1-2-3 superconductors. A model of powerful radiation action on 1-2-3 superconductors has been developed. Low energy mechanism of ablation is developed and the, a processes of modification of thin films and drops generation during film deposition have been explained.
Under UV radiation new absorption bands and photoinduced paramagnetic color centers (PPCC) may appear in a silica glass (v-SiO2) and density of material may increase. These effects must be accounted for in developing laser optics elements based on silica glass, fiber waveguides for UV spectrum range, or in the production processes of the microelectronic components, using the Si/SiO2 films.
This work was aimed at studies into the basic physic—chemical processes govern ing the interaction between the Y203-4BaO-6CuO oxidefilm being deposited and the silicon substrate and the chemical stability of the Y Ba Cu 0 film on the surface 1 2 •3 7—x of S13N4 layer deposited on silicon.
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