Showing papers in "Soviet Journal of Quantum Electronics in 1978"
TL;DR: In this article, a theory of radiative collisions is given, i.e., elementary events in which the emission of a photon occurs in the course of a collision, and an analysis is made of the theoretically predicted effects.
Abstract: A theory is given of radiative collisions, i.e., of elementary events in which the emission of a photon occurs in the course of a collision. Special attention is paid to radiative collisions stimulated by a laser field. Simple but clear approaches formulated in the forties or fifties are described briefly. This theory applies, in particular, to collisions in a strong electromagnetic field which affect the collision dynamics. Chemical radiative collisions, i.e., chemical reactions stimulated by photons absorbed in the course of a collision, are reviewed. An analysis is made of several recent experiments in which the theoretically predicted effects were observed: these include the radiative-collisional transfer of excitation from atom to atom, nonlinear effects due to the influence of the field on the collision dynamics, and photosubstitution of one of the atoms in a halogen molecule with an inert gas atom.
36 citations
TL;DR: In this article, an experimental investigation of rotational and vibrational stimulated Raman scattering (VSTRS) in nitrogen at low pressures (1
Abstract: Results are presented (thresholds of the effects and spectral characteristics) of an experimental investigation of rotational (RSTRS) and vibrational stimulated Raman scattering (VSTRS) in nitrogen at low pressures (1
34 citations
TL;DR: In this paper, a theoretical analysis is made of the possibility of constructing a distributed feedback dye laser in which a doped cholesteric liquid crystal is used as the resonator, and the threshold power density required to obtain stimulated emission from an active dye impurity in the crystal is P≈1×105 W/cm2
Abstract: A theoretical analysis is made of the possibility of constructing a distributed feedback dye laser in which a doped cholesteric liquid crystal is used as the resonator The threshold power density required to obtain stimulated emission from an active dye impurity in the crystal is P≈1×105 W/cm2
25 citations
TL;DR: In this paper, the effect of a breakdown plasma in air and of oxidizing reactions occurring on the surface of metallic targets on the temperature dependence of their effective absorption coefficient was investigated, and a lowering of the threshold for the breakdown of air by pulse-periodic CO2 laser radiation close to a copper target was discovered when the target was heated.
Abstract: The effect of a breakdown plasma in air and of oxidizing reactions occurring on the surface of metallic targets on the temperature dependence of their effective absorption coefficient was investigated. A lowering of the threshold for the breakdown of air by pulse-periodic CO2 laser radiation close to a copper target was discovered when the target was heated. A comparison was made between the kinetics of heating metals in air by means of cw and pulse-periodic laser radiation.
24 citations
TL;DR: In this paper, a GaSb/InGaAsSBS/GaSb heterostructure with an injection current of 900 A/cm2 density at 90° K was obtained at the wavelength of 1.9 μ.
Abstract: Stimulated emission was obtained at the wavelength of 1.9 μ from a GaSb/InGaAsSb/GaSb heterostructure using an injection current of 900 A/cm2 density at 90° K.
23 citations
TL;DR: In this paper, a pulsed Y3Al5O12:Er3+ laser (4I11/2-4I13/2 transition, λ = 2.94 μ) with activator concentrations of 30 wt.% (T = 300 °K) was reported.
Abstract: The development of a pulsed Y3Al5O12:Er3+ laser (4I11/2–4I13/2 transition, λ = 2.94 μ) with activator concentrations of 30 wt.% (T = 300 °K) is reported. A pulse repetition frequency of f = 20 Hz was obtained under free-oscillation and Q-switched conditions. Stimulated emission due to this transition at T = 300 °K was obtained over the whole concentration series of the Y3Al5O12–Er3Al5O12 system with Er3+ concentrations of between 10 and 100 wt.%.
23 citations
TL;DR: In this article, an investigation of the heterogeneous photochemical reaction between Ge and Br2, the Br2 molecule being excited by λ = 514.5 nm high-poiwer argon laser radiation in the predissociation range is presented.
Abstract: Results are presented of an investigation of the heterogeneous photochemical reaction between Ge and Br2, the Br2 molecule being excited by λ = 514.5 nm high-poiwer argon laser radiation in the predissociation range. The dependence of the reaction rate on the irradiation intensity has a well-defined nonlinear character. The explanation of this effect is found by analyzing the chemcal kinetics of this reaction. The possibility of utilizing the heterogeneous photochemical reaction between Ge and Br2 for laser separation of bromine isotopes is discussed.
23 citations
TL;DR: In this paper, the elementary processes and characteristics of a pulsed nanosecond discharge plasma in a copper vapor-buffer gas mixture and their correlation with the laser energy parameters are investigated.
Abstract: An investigation is made of the elementary processes and characteristics of a pulsed nanosecond discharge plasma in a copper vapor–buffer gas mixture and of their correlation with the laser energy parameters. It is shown that the saturation of the stimulated emission power with rising pressure must be associated with a drop in the effective electron temperature. The complex dependence of the stimulated emission energy on the buffer gas (neon) pressure is identified and explained. It is established that at high operating pressures the pulse repetition frequency is governed by the electron cooling rate and by the plasma recombination in the afterpulse interval. At low pressures and for small laser tube apertures the pulse frequency is governed by the quenching of the metastable states by the walls. The excitation conditions are optimized and an efficiency of 2.1 % is achieved.
22 citations
TL;DR: In this paper, a method for the simultaneous determination of the quantum yields of excited and unexcited iodine atoms produced by photodissociation of alkyl and fluoroalkyl iodide molecules was presented.
Abstract: A new method is presented for the simultaneous determination of the quantum yields of excited and unexcited iodine atoms produced by photodissociation of alkyl and fluoroalkyl iodide molecules, and for the determination of the rate constants of the subsequent recombination processes. The method involves taking simultaneous oscillograph traces of the 1313 and 580 nm luminescence signals of the material being studied, produced during molecular photodissociation by neodymium laser harmonics. These constants were determined for CF3I, 1–C3F7I, and (CF3)3CI molecules using the radiation of the fourth harmonic (266 nm) with a pulse energy of 0.4–0.8 J. The results significantly altered the estimate, based on previous investigations, of the possible population inversion in the active medium of a Q-switched iodine laser.
21 citations
TL;DR: In this article, a retroreflecting mirror was used for dynamic compensation of optical inhomogeneities of a laser-active medium for the first time by means of a retro reflecting mirror.
Abstract: Dynamic compensation of optical inhomogeneities of a laser-active medium was achieved for the first time by means of a retroreflecting mirror.
21 citations
TL;DR: In this article, the authors optimized frequency doubling in a KDP crystal, pumped with single pulses of 30 psec duration, and found that, under picosecond pumping conditions, there was a definite optimal relationship between the length of a crystal and pump power density.
Abstract: Frequency doubling in a KDP crystal, pumped with single pulses of 30 psec duration, was optimized. It was found that, under picosecond pumping conditions, there was a definite optimal relationship between the length of a crystal and pump power density. The energy efficiency of conversion to the second harmonic was 92% for a pump power density of 8×109 W/cm2 in a crystal 14 mm long.
TL;DR: In this article, a cholesteric liquid crystal was used as a selective Bragg reflector for tuning and narrowing of the emission spectrum of a dye laser, and the average emission frequency of this laser was a function of the spectral position of the Bragg reflection maximum of the oriented liquid crystal layer.
Abstract: Tuning and narrowing of the emission spectrum of a dye laser were achieved for the first time when a cholesteric liquid crystal was used as a selective Bragg reflector. The average emission frequency of this laser was a function of the spectral position of the Bragg reflection maximum of the oriented liquid crystal layer. The position of the reflection maximum was varied by altering the temperature.
TL;DR: In this article, the power characteristics of the laser transitions in strontium atoms and ions under self-heating conditions were investigated and the average output power was 1.2 W and the efficiency was 0.1% when the repetition frequency of the excitation pulses was 20 kHz in a tube 10 mm in diameter and 380 mm long.
Abstract: An investigation was made of the power characteristics of the laser transitions in strontium atoms and ions under self-heating conditions. The total (over the whole spectrum) average output power was 1.2 W and the efficiency was 0.1% when the repetition frequency of the excitation pulses was 20 kHz in a tube 10 mm in diameter and 380 mm long. About 75% of the output power was concentrated in a line at 6.45 μ.
TL;DR: In this article, the influence of the initial conditions on the development of a homogeneous discharge in the geometry of a typical TEA CO2 laser was studied, the active medium being preionized by ultraviolet radiation from an auxiliary discharge.
Abstract: The influence of the initial conditions on the development of a homogeneous discharge in the geometry of a typical TEA CO2 laser was studied, the active medium being preionized by ultraviolet radiation from an auxiliary discharge. It was established theoretically and experimentally that there is a certain range of values of the initial electron density and electric field, within which a volume-discharge regime is realized, and conditions and equations determining the limits of this range were formulated. The physical model developed explains a number of effects which characterize the operation of transversely pumped pulsed gas-discharge lasers.
TL;DR: In this article, the reflectivity of copper, aluminum, and stainless steel mirrors acting on neodymium-laser pulses was investigated and the results were compared with heating calculations using the linear theory of heat conduction and data from other publications.
Abstract: A study was made of the reflectivity of copper, aluminum, and stainless steel mirrors acted on by neodymium-laser pulses of ~400 nsec duration and ~70 J energy. The temperature and luminosity of the irradiated surface were recorded at the same time. Within an experimental error of ±10%, the reflection coefficient of the mirrors remained constant right up to the energy density at which intense evaporation of the metal occurred. There was a substantial reduction in the reflection coefficient when an absorbing discharge formed in the vapor. The results obtained were compared with heating calculations using the linear theory of heat conduction and data from other publications.
TL;DR: In this paper, a theoretical analysis is made of stimulated light scattering in a pump beam possessing both fine-structure inhomogeneity and a continuously varying amplitude and phase envelope due to focusing of the beam with a lens into an unbounded medium.
Abstract: A theoretical analysis is made of stimulated light scattering in a pump beam possessing both fine-structure inhomogeneity (and thus, "gray" divergence) and a continuously varying amplitude and phase envelope due to focusing of the beam with a lens into an unbounded medium. An equation is derived to describe the gain of the pump-reproducing field component, and a solution of this equation, excitable by spontaneous radiation noise, is found in the constant pump field approximation. In this case, the scattered wave is localized in a narrow (compared with the pump wave) near-axial zone and, unlike scattering in a waveguide, the reproduction of the pump wave is partial and dependent on the correlation between the "gray" and diffraction-limited divergence. The disagreement between this theoretical conclusion and the complete reproduction observed earlier experimentally indicates the importance of saturation effects in the scattering of focused beams.
TL;DR: In this paper, a comparative study of the radiation spectra of spark and surface discharges in the 114-200 nm range is presented, and it is shown that both complete and incomplete discharges are a more efficient source of ultraviolet radiation for preionization of the active volume of CO2 lasers than spark discharges.
Abstract: Results are presented of a comparative study of the radiation spectra of spark and surface discharges in the 114–200 nm range. It is shown that both complete and incomplete surface discharges are a more efficient source of ultraviolet radiation for preionization of the active volume of CO2 lasers than spark discharges. This is attributed to the possibility of concentrating the radiation energy in the required spectral range and of locating the discharge plasma in the optimal position with respect to the laser active volume. An analysis of the time behavior of the radiation intensity of the most characteristic spectral lines showed that the changes in the spectrum of an incomplete surface discharge with polarity reversal of the supply pulse were associated with the surface-discharge-formation mechanism.
TL;DR: In this paper, the influence of the gas-discharge parameters on the specific laser output energy and efficiency of a transversely excited copper vapor laser was investigated, and two optimum buffer-gas pressures were found.
Abstract: The influence of the gas-discharge parameters on the specific laser output energy and efficiency of a transversely excited copper vapor laser was investigated. For a Cu–Ne mixture, two optimum buffer-gas pressures were found. A maximum specific output energy of 55 μJ/cm3 was obtained at an efficiency of 1%. The optimum pulse repetition frequencies for lasing were determined.
TL;DR: In this article, a theoretical study of the amplification and generation of coherent radiation in the optical range based on the undulator mechanism of stimulated magnetic bremsstrahlung from relativistic electrons is made.
Abstract: A theoretical study is made of the amplification and generation of coherent radiation in the optical range based on the undulator mechanism of stimulated magnetic bremsstrahlung from relativistic electrons. Expressions are obtained for the gain and the efficiency. It is shown that the reaction of the radiation plays an important part in the nonlinear saturation regime and in the mode of operation in which the beam is used repeatedly. Physically possible versions of the parameters of an electron laser are given for different spectral regions.
TL;DR: In this article, the influence exerted on the properties of interference copies by the type of the original hologram, gap between this hologram and a copying material, shape of the copying wavefront, and copying radiation wavelength is analyzed.
Abstract: An analysis is made of various hologram copying methods and of the limits of their recommended use. The structure of the near-field Fresnel pattern is considered from the point of view of interference copying of holograms. An equation is derived for a thin copy prepared by the interference method. A study is made of the influence exerted on the properties of interference copies by the type of the original hologram, gap between this hologram and a copying material, shape of the copying wavefront, and copying radiation wavelength. Estimates are obtained of the aberrations of a hologram copy. Special features of the interference copying of Fourier microholograms and their arrays are considered. Hologram copying systems are described.
TL;DR: In this paper, a two-stage electronic excitation of complex organic molecules in solution was performed using a mode-locked Nd:YAG laser, which was frequency-converted by parametric superradiance effect.
Abstract: An apparatus was made for selective two-stage electronic excitation of complex organic molecules in solution. Radiation from a mode-locked Nd:YAG laser was frequency-converted by the parametric superradiance effect. A wavelength tuning rang of 0.26–4 μ, a wavelength-dependent pulse energy of 1 μJ to 1 mJ, and a pulse repetition frequency of 0.5 Hz were obtained.
TL;DR: In this paper, an investigation was made of lasers utilizing the F2, F2+ and F2− centers emitting in the spectral range 0.6-1.26 μ.
Abstract: An investigation was made of lasers utilizing the F2, F2+ and F2− centers emitting in the spectral range 0.6–1.26 μ. Quasi-cw stimulated emission from the F2− centers was obtained as a result of pumping with a cw YAG laser (λ = 1.06 μ). Thermal tuning of the emission frequency was observed and a qualitative explanation of this effect was found. The time stability of the centers and the influence of the pump radiation were studied. A fairly simple method for restoring the F2+ centers was found.
TL;DR: In this paper, the characteristics of dynamic transmission and reflection holograms are considered theoretically, and it is shown that going over to reflection geometry greatly improves the light-beam conversion characteristics (the gain exceeds 70 cm−1 and is independent of the spatial frequency).
Abstract: The characteristics of dynamic transmission and reflection holograms are considered theoretically. It is shown, using the specific example of holograms recorded in electrooptic LiNbO3 crystals, that going over to reflection geometry greatly improves the light-beam conversion characteristics (the gain exceeds 70 cm−1 and is independent of the spatial frequency). It is shown that the period of a recorded holographic grating can be varied by an external electric field.
TL;DR: In this paper, a mechanism for macroscopic damage to transparent dielectrics, resulting from the explosion of small-diameter (≲ 10−5 cm) absorbing inhomogeneities, was proposed.
Abstract: A mechanism is proposed for macroscopic damage to transparent dielectrics, resulting from the explosion of small-diameter (≲ 10−5 cm) absorbing inhomogeneities. The mechanism given is caused by ultraviolet preionization of the matrix surrounding the inhomogeneity and by the appearance in it of free carriers inducing additional absorption. This absorption results in the explosion of the ionized region and thus in the propagation of a discharge. The importance is indicated of induced absorption in a growing crack, caused by charge separation on its walls (the triboelectric process).
TL;DR: In this article, the first overtone of the CO molecule (λ = 2.7-5 μ) was achieved using the electron-beam-controlled method using the CO laser.
Abstract: Stimulated emission at the first overtone of the CO molecule (λ =2.7–5 μ) was obtained for the first time using the electron-beam-controlled method. When the temperature of the active medium was 100 °K and the specific energy input was 120 J liter −1 amagat−1, the overall efficiency of the CO laser with a selective resonator was ~30% and of this, 3% of the energy was emitted as a result of the two-quantum transitions. The maximum radiation energy in the 2.7–3 μ range was 9 J.
TL;DR: In this article, the Huygens-Fresnel principle is used in an investigation of the influence of the diffraction size of the transmitting aperture and internal turbulence scale on the variance of the intensity fluctuations of laser radiation traveling in a turbulent atmosphere.
Abstract: The Huygens–Fresnel principle is used in an investigation of the influence of the diffraction size of the transmitting aperture and internal turbulence scale on the variance of the intensity fluctuations of laser radiation traveling in a turbulent atmosphere. The asymptotic formulas for the relative variance are derived for weak and strong fluctuations in a collimated beam whose transmitting aperture has the Fresnel number satisfying the condition Ω≥1; corresponding formulas are obtained also for a focused beam and a spherical wave. An analysis is made allowing for the deviation of the turbulence spectrum from the power law in the dissipation range. In the case of strong fluctuations the asymptotic behavior of the variance of a spatially confined beam differs fundamentally from the behavior in the case of unbounded (plane and spherical) waves if the coherence radius of the field is much less than the internal turbulence scale. In this case the relative variance reaches saturation at unity for plane and spherical waves, whereas for a confined beam the saturation level is higher and it is governed by internal turbulence scale as well as by the Fresnel number of the transmitting aperture.
TL;DR: In this article, the authors analyzed the process of head-on stimulated scattering by approximate and numerical methods and showed that the formation of quasisoliton pulses of duration τ ≥ 10−1T2, characterized by high conversion efficiency (~50-70%), is possible if the leading edges of the pulses are sufficiently steep.
Abstract: The process of head-on stimulated scattering is analyzed by approximate and numerical methods. It is shown that the formation of quasisoliton pulses of duration τ≈10−1T2, characterized by high conversion efficiency (~50–70%), is possible if the leading edges of the pulses are sufficiently steep.
TL;DR: In this article, an analysis is made of the wavefront reversal in pump beams with a highly developed transverse interference structure. And a calculation of the serpentine effect using a power-series expansion in terms of the intensity of a monochromatic pump beam with a randomly inhomogeneous transverse structure is made.
Abstract: An analysis is made of the wavefront reversal (or reproduction) in pump beams with a highly developed transverse interference structure. When the difference between the pump and scattered field wavelengths is small, diffraction improves the reproduction process. On the other hand, pulling of the scattered field into the cores of diffraction filaments with high pump intensities (as in serpentine active microwaveguides) results in deterioration of the reproduction process but it increases the scattered-field increment. A calculation is made of the serpentine effect using a power-series expansion in terms of the intensity of a monochromatic pump beam with a randomly inhomogeneous transverse structure.
TL;DR: In this article, Alexandrite crystals were grown from a molten mixture of BeO and Al2O3 taken in the stoichiometric ratio, and the dimensions of the crystals reached 10×1×1 cm.
Abstract: A new laser material — alexandrite (BeAl2O4:Cr3+) — was investigated. Alexandrite crystals were grown from a molten mixture of BeO and Al2O3 taken in the stoichiometric ratio. The dimensions of the crystals reached 10×1×1 cm. The absorption spectrum at 300°K consisted of U and Y bands with maxima at 420 and 550–600 nm and of narrow lines B, R'1,2,3, and B1,2 at 465, 650–660, and 678.46–680.27 nm. Cooling to 77 °K shifted the R1,2 lines by 8 A toward shorter wavelengths. Stimulated emission of the R1 line was observed at liquid nitrogen temperature. The stimulated emission wavelength was within the range 679.86–680.33 nm.