Dissipation of laser-radiation energy in the gas surrounding a target in intense plasma formation

For the first time, the dissipation of laser-radiation energy in the gas surrounding a target is investigated under the conditions of intense plasma formation near a surface and the existence of large spots of: irradiation. The parameters of different regions of the heated gas are measured and an energy balance of the process of laser effects is obtained. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 814–817, November–December, 1998.     

Stability of the conditions for excitation of atomic spectra in plasma produced on exposure of copper alloys to laser radiation

We show that the temperature of plasma produced by exposure of copper-zinc alloy specimens to laser radiation changes little (within the limits of random errors) with a change in the conditions of the laser effect and chemical composition of the specimens. With use of electric discharges (a low-voltage spark), systematic changes in the temperature of the plasma are observed when the chemical composition of copper-zinc alloys changes. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 319–321, May–June, 1998.     

Some characteristics of laser refractometric detection in a cylindrical cuvette

Results of sensitivity measurements in laser refractometric detection in a cylindrical cuvette are reported. A model of laser-beam transmission in a capillary with a liquid is developed. The influence of the laser-beam position, capillary and liquid characteristics, and laser power fluctuations on detection sensitivity is discussed. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 894–899, November–December, 1998.     

Dynamics of processes occurring in laser ablation of metals in a liquid

We present the results of investigations undertaken to establish relationships between certain characteristics of the disintegration of metals in air and liquid under laser radiation and their thermophysical properties, as well as between the basic parameters of a gas cavity formed in a liquid and the energy of the laser ablation products of metals. Consideration is given to the possibilities of applying the dynamic properties of this cavity to control the time behavior of the radiation of solid-state lasers and to solve spectroanalytical problems. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave, Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 668–673, September–October, 1997.     

Nonlinear amplitude-tuning characteristic of a CO2 laser with pump-current modulation

The nonlinear amplitude-tuning characteristic of a CO₂ laser with discharge-current modulation was investigated by mean of numerical simulation. It is shown that in the general case the magnitude and shape of the laser response depend on the ratio between the frequency of the pump modulation and the fundamental resonance frequency of the laser. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 68, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 640–644, September–October, 1999.     

Laser system based on a picosecond dye laser with combined feedback for spectroscopy

A laser system comprising a synchronously pumped picosecond dye laser with combined cavity-distributed feedback and a two-stage dye amplifier is described. The dependence of the laser pulse duration on the detuning of the cavity length, the pumping level of the active medium, and the pulse number in the pulse train was investigated. It is shown that the combination of the two types of feedback provides more than ten-fold shortening of the dye laser ultrashort pulse duration. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 47–55, January–February, 1998.     

Studies of spectral and coloristic properties of ultradispersive hematite particles

B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70 F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 6, pp. 157–165, November–December, 1995.     

Recording of selective intracavity absorption at doubled frequencies of multimode laser radiation

We carried out measurements of the spectral distribution of wideband dye laser generation intensity within the limits and in the vicinity of an absorption line with its simultaneous recording at the frequencies of the fundamental and second harmonics of laser radiation. In the laser cavity we placed optical cuvettes with active and absorbing media, as well as selecting and nonlinear-optical elements. We show that at double frequencies the contrast of the narrow-band hole in the multimode laser generation spectrum increases. The gain in the concentration sensitivity of measurements depends in this case on the value of the absorption coefficient being determined. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., 220072, Minsk, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 516–521, July–August, 1998.     

Temperature dependence of the width of spectral holes: Octaethylporphin in polymer matrices

Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 2, pp. 145–150, March–April, 1995.     

Amplitude-detuning characteristic of a CO2 laser with simultaneous modulation of two parameters

Analytical expressions have been obtained in a linear approximation for the amplitude-detuning characteristic of a CO₂ laser with simultaneous modulation of two its parameters. It is shown that the value and form of the laser response can be controlled over a wide range by way of changing the modulation frequency, the value of the detuning, and the phase difference of the oscillations of the simultaneously modulated parameters. B. I. Stepanov Institute of Physics of the Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 190–196, March–April, 1997.     

Spectral-time characteristics of combined-target laser plasma

From the analysis of the contours of the spectral lines of target-material atoms, the electron and atomic concentrations and their variation with time are determined in the laser plasma of a combined Cu–Al–Cu target. The time dependences for the concentrations of electrons and atoms in the ground and excited states are explained within the framework of a model that allows for plasma decay being determined by processes of three-particle recombination and ionization as well as by the variation in the particle concentration in plasma expansion. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 426–432, May–June, 1998.     

Laser absorption and fluorescence diagnostics of a plasma

Diagnostics of a near-surface laser plasma, the plasma of a strong-current pulse gaseous discharge in inert gases, nitrogen, and carbon dioxide under conditions of intense evaporation of the wall of the discharge chamber, the plasma of a discharge with a hollow cathode, and the active medium of an excimer laser was conducted by methods of intracavity laser spectroscopy and laser-induced fluorescence. The dynamic fields and absolute concentrations of atoms, ions, molecules and electrons, the plasma temperature, and the velocities of flows of particles were measured. The quantitative determination of the density of particles in the erosion laser flame prior to breakdown and the phenomena associated with the formation of molecules in the laser plasma received primary consideration. To whom correspondence should be addressd. Instite of Molecular and Atomic Physics of the Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 281–290, May–June, 1997.     

Neodymium lasers with fiber-optic reflectors

The lasingin an Nd:YAG laser with a fiber-optic reflector in the form of a loop was experimentally investigated. Two designs of the laser with a fiber-optic loop reflector were considered. In the laser of the first type the reflector was formed by a fragment of a fiber guide the ends of which were placed in the focal plane of a microscope objective. In the laser of the second type the role of the output mirror was played by a loop-shaped fiber-optic reflector made on the basis of a V-shaped fused three-fiber splitter. It is shown that when such lasers operate in the regime of free-running lasing, in them there takes place the effect of nonlinear conversion of the generated radiation frequency in the Stokes and anti-Stokes regions of the spectrum. Institute of Applied Optics, National Academy of Sciences of Belarus, 11, Belynitskii-Birulya Str., Mogilev, 212793, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 259–262, March–April, 1999.     

Excited states, relaxation processes, and coordination reactions in the active centers of heme proteins

Based on the results of studying hemoglobin and myoglobin molecules using the methods of laser absorption spectroscopy of superhigh time resolution, we described photophysical and spectral properties of excited states, and intramolecular electronic and thermal relaxation processes. A mechanisms of the photodissociation reaction of oxy forms of these proteins is proposed and substantiated. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 479–482, July–August, 1999.     

Determination of optical density at the center of an absorption line contour from the spacing between the frequencies of the two-component radiation spectrum of a laser having a phase-polarization selector

A method for determining optical density at the center of an atomic absorption line contour from the spacing between the components of the two-frequency generation spectrum of a laser with a phase-polarization selector is suggested. It is shown that the method makes it possible to measure the largest possible optical densities, but it is not suitable for measuring optical densities smaller than unity. Optical densities at the center of the D-lines of sodium are measured experimentally. A good agreement between experimental and predicted data is obtained. Institute of Molecular and Atomic Physics of the Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 738–743, November–December, 1997.     

Study of the profiles of atomic absorption lines in an electrothermal atomizer

Narrow atomic absorption lines of Ba, Cs, Mg, and Tl are recorded in an electrothermal atomizer with a graphite tube furnace by the intracavity laser spectroscopy method. The conditions of applicability of this laser absorption method for reducing the observed profiles of spectral lines to the true ones are found. Measurement of the integral absorption coefficient has made it possible to determine the absolute number of free atoms of each element in the analyte volume at the maximum of the absorption peak under optimum conditions of atomizer heating. The Voigt parameters are determined from the profiles of absorption lines. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 27–33, January–February, 1998.     

Control of the shape and duration of a laser pulse in the case of nonlinear total internal reflection

A nonlinear device based on nonlinear total internal reflection is suggested which provides a more than ten-fold shortening of the laser pulse and smooth variation of the pulse duration due to double reflection from the interface between transparent and absorbing media. Results are presented for the shape and duration of the pulse components that have been reflected and transmitted by the interface. B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., 220072, Minsk, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 325–328, May–June, 1997.     

Luminescence of human blood serum in the longwave spectral region

An investigation is made of the absorption, fluorescence, and fluorescence excitation spectra of human blood serum whole and diluted with a sodium-phosphate buffer solution. Time characteristics of the longwave serum luminescence are obtained. The quantum yield of background fluorescence upon excitation by radiation with λexc=500 is found to be 0.5%. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 433–436, May–June, 1999.     

Properties of lasers based on vapors and solutions of complex organic compounds

We present the most important results of investigations of lasers based on vapors and solutions of complex organic compounds. We investigated the effect of a foreign gas, the duration and intensity of the exciting pulse, the temperature of the active medium, and the spectroscopic parameters of the material on the generation characteristics of complex molecules in the gas phase. The special features of generation of radiation by a laser with distributed feedback in transition from a condensed to the gas phase in heating the active medium are considered. It is suggested that the polarization characteristics of the radiation generated by a vapor laser be used to investigate the laws that govern the relaxation of optically induced anisotropy of excited molecules of the active medium. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 709–720, September–October, 1998.     

Dynamics of erosion plasma formation and formation of a plasma flame with a condensed disperse phase when quasi-continuous laser radiation acts on bismuth

The dynamics of near-surface plasma formation and the formation of an erosion plasma flame was investigated for quasi-continuous laser radiation (λ=1.06 μm, q=0.1–10 MW/cm², τ∼1.5 msec) acting on bismuth targets in air. The absence of low-threshold plasma formation at q<2 MW/cm² was established and explained. Instabilities in the plasma formation were revealed and the range of laser radiation power densities (2≤q≤4 MW/cm²) at which these instabilities take place was determined. At q≥5.4 MW/cm², brightening of the flame was noted. The dependence of the luminescence temperature of the flame on the laser radiation power density q was determined. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 126–133, January–February, 1998.