Lasers in Medicine
Year:2010 | Volume:7 | Issue:3 (37)|Papers Count:6

Introduction: Due mainly to the extensive use of antibiotics, the spread of drug-resistant bacteria is one of the most worrying threats to public health. One strategy can be used to overcome potential shortcomings might be the inactivation of these organisms by photodynamic therapy. In this study, we have investigated whether multidrug-resistant wound-associated organisms (methicillin-resistant Staphylococcus aureus, methicillin-resistant Staphylococcus epidermidis and ESBL-producing Escherichia coli) are sensitive to lethal photosensitization using the dye methylene blue (MB) coupled with laser light of 660 nm.Material and method: Effect of photosensitizer concentration (25, 50, 100 µg/ml) and laser light dose (27.3, 54.6 and 109.2 J/cm2) on lethal photosensitization was investigated.Results: All species were susceptible to kill by photodynamic inactivation. The bactericidal effect was not dependent on the concentration of methylene blue; but it was dependent on the light dose. Methylene blue photosensitization using red laser light (109.2 J cm-2) was able to achieve reductions of 99.03% and 98.95% in the viable counts of S. aureus and S. epidermidis (using starting concentrations of 104–105 CFU ml-1). Kills of 92.23% were obtained for E. coli (initial concentration 104–105 CFU ml-1) photosensitized by the red light (109.2 J cm-2).Conclusion: These findings imply that methylene blue in combination with red light may be an effective means of eradicating multidrug-resistant bacteria from wounds.

Introduction: Over the past decade, applying quantum dot lasers have attracted increasing attentions. Because of high tenability and thus high flexibility of output power of such lasers, they have found numerous applications especially in the field of fine tissues surgery and tomography. Due to unique properties, quantum dots have better characteristics and even more privileged than common and quantum well lasers. In order to establish phase conjugation, Laser gain media, the main part of laser arrangement, have a non-zero value of nonlinear optical susceptibility. In the present study, we are trying to investigate the possibility of making variations in the mentioned property and hence tuning the output strengths of the produced laser. To conduct this, the use of fundamental theories of the principal optical transitions and combination with the concepts of quantum confinement, third order non-linear optical susceptibility of typical CdTe nanocrystallite for different parameters has been evaluated and also the related variations have been investigated.Material and Methods: In this study, excitonic effects on the third-order nonlinear optical properties in disk-like parabolic quantum dots are studied and the exciton oscillator strength and the third-order nonlinear optical susceptibility due to excitons in the parabolic quantum dots are analyzed theoretically. Finally, numerical results are presented for typical CdTe parabolic quantum dots. In order to access the related articles, some websites like Elsevier, IOP and American Physical Society (APS) have been searched.Results: The real and imaginary parts of third-order nonlinear optical susceptibility of nanostructured CdTe have been calculated and the dispersion diagram for excitation frequency of 5×1013Hz was plotted. Afterwards, the third-order nonlinear optical susceptibility was investigated for different photonic confinement frequencies. The position of exitonic resonance peak shifts right when the parabolic confinement frequency ω0 increases which predicts the blue-shift of strong induced confinement in semiconducting quantum dot.Conclusion: The results show that the third-order nonlinear optical susceptibility is greatly enhanced because the excitons are quantized enough in the quantum dots. This makes the parabolic quantum dots as a promising candidate for nonlinear optical applications specially in the semiconducting lasers with high tenability.

Introduction: Ultrashort laser pulse heating has recently attracted much attention about selective damage for cancer cells, bacteria, viruses and DNA. Short pulses concentrate high laser energies on extremely small metallic nanoparticle, and the photons are absorbed by free electrons within the metal and transferred to the lattice subsystem and then to the surrounding medium. Therefore, this nanoparticle provides highly selective heat transfer from ultra-short pulses to the target cells. Simulation of this process provides an effective method and the results of it can be used for further nano medicine practical research.Material and methods: Among different nanostructures, gold nanoparticles are the most promising candidates for photo thermal process since they are strong absorbers, photostable, and nontoxic, easily conjugated to proteins and have adjustable optical properties. There are two models for calculating temperature of electrons and crystal lattice of nanoparticles. The first temperature model utilizes similar temperatures for electrons and lattice and the second temperature model that is used for ultrashort laser pulses. Short pulses are ended before complete transfer of electron energy to the lattice and then the temperature of electron and lattice is different. In this paper, simulation results on the heating process of gold nanoparticles after irradiation by ultrashort laser pulses femtosecond, picosecond and nanosecond are presented. We use a model utilizing the uniform heating approximation and the small size of nanoparticles in comparison to the wavelength of laser radiation, and then it was confirmed that this model is appropriate approximation for nanoparticles heating in the femtosecond, picosecond and nanosecond regimes. It shows that during the laser pulse duration. The transfer of heat from the nanoparticles into the surrounding media is slight but when the laser pulse has degraded, the transfer of heat from the particle to the surrounding medium becomes increasingly important. In nanosecond regime, because of longer pulse duration, this heat transfer is higher than others and the temperature of particle rapidly decreases. The effects of the different biological surrounding media blood, human prostate, tumor and fat are investigated.Results: Due to the relatively low thermal conductivity of fat as compared to the other biomedia fat has low thermal characteristics and we observe higher heating of the particles at the same energy level and pulse duration. This study will compare thermal calculations for 30 nm gold nanoparticles, which are heated and cooled in water at different heat that losts transfer rates for femtosecond, picosecond and nanosecond regimes. The temperature dynamics of the particle is sensitive to the temperature dependence of the heat lost from the surface of the nanoparticles into the surrounding medium. In the femtosecond regime, pulse duration is very small and medium with high thermo physical characteristics cannot change the temperature greatly, but in the picoseconds and nanosecond regimes, medium with low thermal conductivity can alter the temperature of nanoparticles very much. By reviewing the other research, it is confirmed that theoretical results coincide to practical attempts. Maximum temperature for femto, pico and nanosecond is 1020, 1005 and 7000 K for 1mJ/cm2, 1mJ/cm2 and 10mJ/cm2 pulse laser intensities respectively. Also it is concluded that two temperature model only are used to femtosecond regime that electron temperature is different from lattice temperature, but this method is not used for longer pulses (pico & nano second pulses) and because of ignoring heat transfer to surrounding medium, its results are not correction.Conclusion: Results of this article show the first temperature model is appropriate method for understanding short laser pulse interaction to metallic nanoparticles, So that for nanoparticles that are smaller than laser wavelength, time delay is negligible and results are similar to the second temperature model.

Introduction: With writing the special code based on Grid search technique, best method for describing the elements energy spectrum is introduced. This method is suitable for investigation of Atomic, molecular and nuclear Energy spectrum, laser pulses and study of spectrum that obtained by laser interaction with cell and human body.Microraman spectrum of eye lens that fitted by De. Mul and time spectrum of one molecule that excited by 585 nm laser and fitted by Gnu plot software. In a special application, this method is used for 22Na spectrums.Material and Methods: For fitting mathematical function to a set of experimental data, the first step is seeing data plot in every software. Then, an initial mathematical function is guessed and the function parameters change as far as possible for initial fitting. After this step, by using this special code based on Grid search technique, is the X2 changes between function data and experimental data are compared. If the X2 is high, it will reduce by introducing small change in every parameter of mathematical function. This is done step, by step, so the X2 reaches to the lowest.Results: By this method, we can have the formulation of element energy spectrum. For example, the equation of 22Na energy spectrum’s description with least squares fitted by experiment data is: N=199.0477 +76100EXP (0.00167 (E-508.7539) 2) + 75100EXP (0.00168 (E-509.2428) 2) + 3450.8070 EXP (0.0000831(E-655.356) 2) + 4002.813EXP (0.0001431(E-839.401) 2) + 11000EXP (0.00105 (E-1048.0230) 2) Fitting start with fit parameter X2=1107.6 and finished with X2 =44.16.Conclusion: By using the special code based on Grid search technique, we try to introduce the best method for describing of the elements energy spectrum.

Introduction: Purpose active material is one of the important components of solid state laser. Solid state laser were called base on active material. That emit in specific wavelength. Target of this work is fabrication of laser glass as new host laser active material for achieving visible laser.Fabrication method: These glasses with composition in mol% of 42.5P2O5, 12Na2HPO4, 25CaF2, 15NaF, 5SiO2, 0.5Nd2O3 were prepared. These glasses were fabricated by heat melting method. Thermal properties of the glasses were investigated by thermal analysis. Absorption in infrared and visible range by Eclipse varion set were took. Up conversion luminescence measurement in the 1064 nm were performed with Nd:YAG laser and S100 spectrometer.Results: Glass transition temperature 640oC and glass crystallization temperature 700oC were obtained. Absorption spectra indicate wavelength picks in 426, 496, 510, 525, 582, 746, 802 and 874 nm that are in agreement with those found in previous reports. According to the up conversion emission, the emission bands were achieved at 560, 620, 640nm.Conclusion: In the research work, fabrication of Nd3+ doped oxyfluorophosphate glasses was sucsesfull. In which observed up coversion properties of infrared to visible range.