Near- and mid-infrared laser radiation interaction with eye tissue

Comparison of the eye tissue transmission for laser radiations with the wavelengths 0.75, 1.08, 1.34, 1.44, 1.54, 1.66, 2.01, 2.69, and 2.94 μm was made with the aim to understand the possible tissue injury by the particular light. From the step by step transmission measurements of the various human eye tissues (in vitro) it was recognized that the value of the transmitted energy in particular segments is different for various wavelengths yielding substantial fluence differences on the retina and anterior segments, mainly.     

Modulation effects in the electron spin echo resulting from hyperfine interaction with a nucleus of an arbitrary spin

Exact analytic expressions for the modulation effects in two- and three-pulse electron spin echoes resulting from the hyperfine interaction of an electron and a nucleus with an arbitrary spin are derived. The two-pulse envelope modulation is calculated numerically for some nuclei for which modulation effects are most often observed experimentally. Applicability requirements of the conventional approximate formula for analysis of the ESE modulation effects are considered.     

Characteristics of target interaction with high power UV laser radiation

Thermal conduction, mass ablation rate, pressure and preheat were investigated in the interaction of a frequency tripled Nd: glass laser of power 0.-0.2 TW with flat targets. In the range $\text{10}{}^{13}\text{?10}{}^{15}\text{W}\text{cm}{}^2$ for 400 ps pulses we find: (a) thermal conduction may be described by a flux limiter f = 0.04 ± 0.01; (b) the mass abaltion rate depends on the incident laser irradiance as $\text{m}\text{?}\text{= 4.4 × 10}{}^5\text{(I/10}{}^{14}\text{)}{}^{0.53}\text{g cm}{}^{-2}\text{s}{}^{-1}$; (c) the pressure near the ablation surface increases approximately linearly with irradiance and is about 70 Mbar at 10¹⁵ W/cm², and (d) preheat as evidenced by K_α X-ray line emission is significantly lower than in λ = 1.05 μm irradiation.     

Features of laser radiation interaction with metals having cryogenic temperature

In this paper we determine the features of the thermophysical processes involved in the interaction of laser radiation with metals that have cryogenic temperature. To do so, we use a one-dimensional model that involves heating a semi-infinite solid by a point thermal source with a constant flux density. Temperature fields, heating and cooling rates in the laser-irradiated zone for iron and titanium at the ambient temperatures of 77 (liquid nitrogen), 293 and 573 K were calculated. The intensity of the laser irradiation enabled the melting temperatures of 1933 K and 1812 K on the Ti and Fe surface, respectively, to be reached. The duration of the laser pulse was 4.5 ms. We show that a drop in ambient temperature from 573 to 77 K leads to a rise in cooling rate from 3.25 × 10³ and 6.4 × 10⁶ K/s to 4.25 × 10³ and 1.3 × 10⁷ K/s in the Ti and Fe targets, respectively. Agreement was good between the calculated depths of melting and phase transformation isotherms and the experimental depths of the interfaces of melting and heat-affected zones.     

Cyclic interaction of Na atoms with circularly polarized laser radiation

Cyclic interaction of Na atoms with laser radiation is under consideration. In the experiment cyclic interaction was conducted through preliminary optical pumping of the atom into the ground state F = 2, M_F = 2 by a single-mode cw dye laser. The results of optical orientation of Na atom and cyclic interaction under different conditions of atomic excitation are presented. Possible applications of cyclic interaction of atom with radiation for detection and cooling of atoms is under discussion.     

An improved transmission line laser model for multimode laser diodes incorporating thermal effects

An improved transmission line model to study the thermal effects in semiconductor laser diodes is reported in this paper. The temperature effects in the laser characteristics are obtained by incorporating temperature dependent gain and carrier density equations for the laser cavity. These primary factors are introduced in the regular transmission line laser model to estimate the static and dynamic characteristics of an 1.3μm InGaAsP double heterostructure laser diode. The results show good agreement with the experimental observation and solution of rate equations referred in the literature. The key feature of this model is that it provides the laser spectra at various temperatures. Based on the model, time dependent evolution of optical spectrum, temperature dependent optical output and frequency chirp are evaluated. Further the distribution of photon and electron density within the cavity is also determined.     

Neutron enhancement from laser interaction with a critical fluid

We discuss experimentally and theoretically neutron production from the laser driven explosion of gas clusters prepared near the liquid-gas critical point. We let deuterated methane that was prepared very close to its critical temperature and pressure expand through a conical nozzle to create clusters, and then irradiated those clusters with a high intensity pulse from the Texas Petawatt Laser. After ionization, the clusters explode producing energetic ions, some of which fuse with resultant neutron emission. We show that the critical fluctuations present in the nozzle before the expansion influence the dynamics of neutron production. Neutron production near the critical point follows a power law, which is a signature of a second order phase transition and it is consistent with the Fisher model. This result might be relevant for energy production from fusion reactions.     

Theory of the interaction of intense laser radiation with magnetoactive plasma

Analytical expressions for the density of magnetoactive plasma perturbed by circularly polarized relativistically strong laser radiation are obtained.     

Biophotonics of the interaction of low-intensity laser radiation with blood erythrocytes

We have studied experimentally how optical radiation affects the neutralization of the toxic action of heavy metals and harmful chemical compounds (ecotoxicants) on the oxygen-transport function of blood erythrocytes. It has been found that the optical radiation has a stabilizing effect and prevents lowering the erythrocyte concentration in the presence of phenol and heavy metals in blood. We have studied the neutralization efficiency of the toxic action of ecotoxicants in relation to the laser irradiation time. The obtained data on the effect of the laser radiation on the thermal denaturation of hemoglobin and erythrocytes yield the scientific substantiation to the development of the optical method for the use in medicine upon drawing and conserving donor blood. We have shown that the obtained data can be used in medicine for improving the reliability of conditions of conservation and storage of donor blood, as well as for preventing the toxic action of harmful chemical compounds in the environment.     

Nonstationary thermal self-action of partially coherent laser radiation

Nonstationary thermal self-action of laser radiation with limited spatial coherency is analyzed using the nonlinear phase channel technique. Specifically, the main effects related to random field modulation are considered. The nonmonotonic change of correlation radius along the pulse length is explained. The results obtained are in good agreement with data of laboratory and numerical experiments.Moscow State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 2, pp. 136–141, February, 1991.     

Numerical analysis of thermal effects in InGaAs system vertical-external-cavity surface-emitting laser

The temperature, the heat flux, and the temperature gradient in an InGaAs system vertical-external-cavity surface-emitting laser are numerical studied by the use of the finite element method, and the analysis is focused on the maximum temperature rise in the active region under various conditions. The effect of substrate thickness on the peak gain of quantum wells, the influence of pump spot radius on the maximum output power, and the spontaneous emission wavelength under different pump power are examined respectively.     

Multifrequency laser radiation and its nonlinear power type interaction with matter

Results of a computer experiment on the statistical factor of multifrequency laser radiation are presented for different numbers of modes and types of nonlinear processes. The gaussian form of the laser light spectrum and the data processing method are taken into account. The model of multifrequency laser radiation used is in agreement with known experimental results.     

Features of the interaction of near-infrared laser radiation with Yb-doped dielectric nanoparticles

Experimental data have been presented to confirm the thermal nature of broadband visible radiation emitted from Yb³⁺- and Er³⁺-doped nanocrystalline particles of orthophosphates and orthophosphate hydrates irradiated by 972-nm near-infrared laser radiation. The mechanism of appearance of this radiation has been discussed.     

Production of heavy atomic clusters upon interaction of laser radiation with matter

The results of an investigation of the formation of Pb, Th, and U clusters over a broad range of numbers of atoms (from a few atoms to macroparticles) upon interaction of high-power pulsed laser radiation with matter are presented. Clusters of fissionable elements are studied for the first time. A setup for determining the yield of clusters and the number of atoms in them, which is based on the use of several different methods (laser resonance fluorescence, time-of-flight measurements, and counting the number of tracks of fission fragments from the cluster nuclei), is described. The dependence of the yield of clusters with various numbers of atoms on the conditions for their formation is discussed. Zh. éksp. Teor. Fiz. 112, 78–88 (July 1997)     

Investigating the interaction of x-ray free electron laser radiation with grating structure

The interaction of free electron laser pulses with grating structure is investigated using 4.6±0.1 nm radiation at the FLASH facility in Hamburg. For fluences above 63.7±8.7 mJ/cm², the interaction triggers a damage process starting at the edge of the grating structure as evidenced by optical and atomic force microscopy. Simulations based on solution of the Helmholtz equation demonstrate an enhancement of the electric field intensity distribution at the edge of the grating structure. A procedure is finally deduced to evaluate damage threshold.