Mode competition effects in CW dye lasers

The output characteristics of a rhodamine 6G jet stream cw dye laser equipped with a mirror grating combination for mode selection, have been studied experimentally. The tuning range proved to be considerably narrower than that to be expected from the gain profile under the (erroneous) assumption of independently oscillating modes. Actually, the reduction of the tuning range is a consequence of mode competition, as pointed out in a previous theoretical paper. Moreover, the intensity of the selected mode has been found to be independent of the wavelength. All experimental findings are in a good agreement with the results of a theoretical analysis.     

UV picosecond laser-induced formation of amino acids from aqueous solutions of ammonic salts of dicarboxylic acids

It is shown for the first time that the irradiation of the ammonic-salt aqueous solutions of the dicarboxylic acids by powerful ultrashort uv pulses provokes the formation of the related amino acids. The amino-acid quantum yield depends on the intensity and for the aspartic acid, in particular, it reaches 40% at the intensity of about 1 GW/cm².     

Model for Optimization of the UV‐A/Riboflavin Strengthening (cross‐linking) of the Cornea: Percolation Threshold

To achieve the maximum level of collagen strengthening within the shortest treatment time possible, we have developed a mathematical model which is used to optimize the process of corneal cross‐linking. This model is able to predict the temporal and spatial distribution of generated cross‐links within the corneal stroma and hence the increase in the elasticity modulus. Theory predicts corneal strengthening at low radiation intensities and the absence of the strengthening effect at radiation intensities above the threshold level, which agrees with the experimental results. The model takes account of the initial riboflavin concentration and bleaching, light intensity and time of illumination.     

High quantum yield of photochemical reactions of protoporphyrin-IX induced by powerful ultrashort laser pulses

The action of powerful pulsed picosecond radiation from a Nd: YAG laser (λ=530 nm, pulse energy: 0.01 J, intensity: 2GW/cm²) and an argon laser (λ=515 nm, power: 50 mW) on protoporphyrin-IX dimethylether in three solvents (trichlormethane, carbon tetrachloride, dioxane) has been studied. Under continuous irradiation the quantum yield and resulting products do not differ materially from the ones produced under mercury lamp irradiation. When irradiation is performed by powerful laser pulses of picosecond duration the quantum yield of photodecomposition of protoporphyrin-IX dimethylether inereases substantially: by 10 in dioxane, by 4 in carbon tetrachloride and by 100 in trichlormethane. It is assumed that a quite different mechanism of multistep excitation is responsible for photodecomposition under powerful picosecond pulses.     

Modifying the collagen framework of costal cartilage under the impact of UV and a flavin mononucleotide

Modifications of the matrix of the tissue of costal cartilage under the impact of UV (λ = 365 nm) and a flavin mononucleotide (FMN) is studied. The changes in the macroscopic properties of the tissue are detected by means of differential scanning calorimetry and under the conditions of uniaxial compression during mechanical testing. The endothermic effects of the denaturation of the collagen framework of the tissue and the Young’s modulus are determined. It is shown that the presence of a flavin mononucleotide in the interstitial fluid leads lowers the temperature of collagen denaturation by 2.5°С and doubles the Young’s modulus. It is found that the temperature of denaturation and the Young’s modulus grow gradually after treating the tissue with the UV radiation, and their values ultimately exceed by far the corresponding values for intact samples. It is concluded that the obtained data indicate the possibility of stabilizing the framework of the matrix of costal cartilage under the impact of UV radiation and a flavin mononucleotide.     

Upconversion nanoparticles for tumor imaging with near-infrared radiation

Prospects for using upconversion nanoparticles as markers for tumor optical imaging are discussed. Using a model of epidermoid Lewis lung carcinoma engrafted in mice, luminescent signals from nanoparticles delivered into the tumor tissue are registered in vivo.     

Three-Dimensional Luminescence Tomographic Visualization of Biological Tissues

Optics and Spectroscopy - We propose a method for obtaining a fluorescence tomographic image for visualization and diagnosis of tissues of a living organism. The method is based on the excitation...     

Selective Photochemical Reaction of Ortho-Iodihe Molecules Excited by Laser Radiation

Results of an experimental study the reaction between electron-excited I₂-molecules and an olefine (2-hexene) are given. It is shown that the reaction proceed with excited I₂-molecules directly and it is highly selective. Selectivity of the reaction hes been studied primarily on the basis of binding of ortho-I₂ molecules. Laser separation of ortho-I₂ and para-I₂ molecules has been accomplished in the paper.     

Dynamics of uv excimer laser ablation of pmma,caused by mechanical stresses theory and experiment

A quantitative model of PMMA ablation was developed. Photochemical reactions, heating of the polymer and mechanical stresses were taken into consideration. The increasing of the optical absorption during the photochemical reaction caused by ArF laser radiation was investigated. The developed model allowed to evaluate the ablation parameters.