Showing papers in "Soviet Journal of Quantum Electronics in 1989"
TL;DR: In this paper, a coherent photogalvanic mechanism of the effect of second harmonic generation on optical fiber length was proposed, and a new method for nondestructive determination of the dependences of the efficiency of second-harmonic generation on the length of the fiber was developed and implemented.
Abstract: Temperature-controlled phase matching was observed in photoinduced second harmonic generation in optical fibers. A new method for nondestructive determination of the dependences of the efficiency of second harmonic generation on the length of the fiber was developed and implemented. A coherent photogalvanic mechanism of the effect is proposed.
70 citations
TL;DR: In this paper, a detailed model of radiative collisions was used to consider three approximations employed in determination of the level populations and of the gain G in the short-wavelength part of the far ultraviolet range.
Abstract: The example of multiply charged Ne-like ions and a detailed model of radiative collisions are used to consider three approximations employed in determination of the level populations and of the gain G in the short-wavelength part of the far ultraviolet range. If the plasma heating process is fast, which corresponds to the transient approximation, the gain can reach G ~ 102 cm − 1. A population inversion appears then not because of strong radiative depletion of the lower active level, but because of transient radiative collisional processes. There is therefore no need to limit the transverse dimensions of a plasma in establishing optical transparency conditions and there are several other consequences of practical importance.
61 citations
TL;DR: In this paper, the threshold, energy, spectral, and temporal characteristics of the output radiation under lasing and regenerative conditions were investigated in a system with self-pumped "loop" phase-conjugate mirrors.
Abstract: Lasing was observed in a system with self-pumped "loop" phase-conjugate mirrors in YAG:Nd3+, KGW:Nd3+, and GSGG:Cr3+:Nd3+ active media. An investigation was made of the threshold, energy, spectral, and temporal characteristics of the output radiation under lasing and regenerative conditions.
57 citations
TL;DR: In this paper, the second harmonic of CO2 laser pulses was achieved in GaSe single crystals at repetition frequencies up to 100 Hz, and phase-matching angles were measured for GaSe at pump wavelengths of 9.3, 9.6, and 10.6 μm.
Abstract: Efficient generation of the second harmonic of CO2 laser pulses was achieved in GaSe single crystals at repetition frequencies up to 100 Hz. The phase-matching angles were measured for GaSe at pump wavelengths of 9.3, 9.6, 10.3, and 10.6 μm. The threshold power densities for surface optical damage and for the formation of a plasma jet on the surface of GaSe were determined. The efficiency of second harmonic generation in a GaSe crystal 0.65 cm thick was up to 9%. A comparison was made of GaSe and ZnGeP2 crystals as materials suitable for the generation of the second harmonic of CO2 laser radiation.
38 citations
TL;DR: In this paper, an analysis is made of the kinetics of the processes occurring in gaseous media that contain molecules of singlet oxygen and iodine, and the available results are used to propose the recommended (most probable) values of the rate constants of the relevant reactions.
Abstract: An analysis is made of the kinetics of the processes occurring in gaseous media that contain molecules of singlet oxygen and iodine. A review is given also of the rates of homogeneous electronic–electronic (EE) energy exchange processes, electronic–translational (ET) quenching, chemical reactions of dissociation of molecular iodine, and heterogeneous quenching on the walls. The reliability of the kinetic schemes of the various processes is confirmed by the agreement between the calculated results and the experimental data. The available results are used to propose the recommended (most probable) values of the rate constants of the relevant reactions.
28 citations
TL;DR: In this paper, the authors developed a stable pulsed yttrium aluminate laser with hybrid mode locking and passive intracavity negative feedback utilizing a GaAs laser, which emitted bandwidth-limited pulses of 4.5 ± 0.5 ps duration with an energy instability of 1.5%.
Abstract: The development of a stable pulsed yttrium aluminate laser with hybrid mode locking and passive intracavity negative feedback utilizing a GaAs laser is reported. The laser emits bandwidth-limited pulses of 4.5 ± 0.5 ps duration with an energy instability of 1.5%.
28 citations
TL;DR: In this paper, the authors demonstrated that the spatial and amplitude characteristics of the?2 radiation can be controlled by modulating the losses of the 1.064 and 1.318 wavelengths, respectively, by introducing nonlinear losses.
Abstract: Simultaneous emission of two wavelengths, ?1 = 1.064 ?m and ?2 = 1.318 ?m, from a cw solid-state YAG:Nd3+ laser was achieved and studied experimentally. It was demonstrated that the spatial and amplitude characteristics of the ?2 radiation could be controlled by modulating the losses of the ?1 radiation. It was established that the stability of the radiation power at the two wavelengths could be enhanced by introduction of nonlinear losses. The emission of two cw series of pulses at wavelengths ?1 and ?2, and tuning of their relative delay was achieved.
22 citations
TL;DR: In this paper, a review of the main results obtained in the last few years in the course of development and studies of integrated injection laser arrays is given, where the main configurations of such arrays are considered: they differ in respect of the structure of the active elements and methods used to couple the elements optically.
Abstract: A review is given of the main results obtained in the last few years in the course of development and studies of integrated injection laser arrays. The main configurations of such arrays are considered: they differ in respect of the structure of the active elements and methods used to couple the elements optically. The main approaches to calculations of the mode compositions of the output radiation are described. The experimental energy, spectral, spatial, and dynamic parameters of laser arrays are reported to illustrate the attained levels of their technical characteristics. An analysis is made of phase locking of the radiation from laser arrays by injecting an external phase-locking optical signal, and also by using a shared external resonator, spectral–spatial selectors, and other external optical components.
20 citations
TL;DR: In this paper, an optimal method was developed for generating the fifth harmonic (λ = 216 nm) with an output energy of 0.5 mJ in the form of pulses of 15-ps duration.
Abstract: An investigation was made of the generation of the fifth harmonic of the radiation emitted by a picosecond Nd3+-activated yttrium aluminate laser. The harmonic was generated by three different methods using KDP and potassium pentaborate crystals. An optimal method was developed for generating the fifth harmonic (λ = 216 nm) with an output energy of 0.5 mJ in the form of pulses of 15-ps duration.
17 citations
TL;DR: In this article, an experimental investigation was made of a Raman laser emitting picosecond optical pulses from an LiIO3 crystal, pumped synchronously by a train of pulses from a phosphate neodymium glass laser with mode self-locking (λp = 1.054 μm).
Abstract: An experimental investigation was made of a Raman laser emitting picosecond optical pulses from an LiIO3 crystal (λl = 1.143 μm), pumped synchronously by a train of pulses from a phosphate neodymium glass laser with mode self-locking (λp = 1.054 μm). The time characteristics of the Raman laser radiation were determined as a function of the mismatch of the resonator lengths. When the resonator lengths were matched, the duration of the output pulses was shortened by a factor of 7 or 8 compared with the pump pulses. In this case, the duration of the output pulses was ~ 1 ps and the energy conversion efficiency was ~ 30%.
17 citations
TL;DR: The feasibility of compression of a high-power optical pulse by stimulated Brillouin scattering in a laser plasma under conditions of amplification of a Stokes pulse from the thermal noise level, allowing for optical heating of the plasma, is studied for the first time in this article.
Abstract: High-power ultrashort optical pulses are obtained by compression under conditions of stimulated scattering in nonlinear media, although the radiation intensities used are generally limited by the possible breakdown of the medium. The feasibility of compression of a high-power optical pulse by stimulated Brillouin scattering in a laser plasma under conditions of amplification of a Stokes pulse from the thermal noise level, allowing for optical heating of the plasma, is studied for the first time. It is demonstrated that a laser plasma may be a convenient medium for appreciable compression of high-power long-wavelength subnanosecond pulses to durations of a few tens of picoseconds and for compression of short-wavelength pulses from a few tens of picoseconds to the subpicosecond range.
TL;DR: In this paper, the coherent anti-Stokes Raman scattering (CARS) method was used in observation of excited Al II, Al III, In II and N II in an optical breakdown plasma.
Abstract: The coherent anti-Stokes Raman scattering (CARS) method was used in observation of excited Al II, Al III, In II and N II in an optical breakdown plasma. The feasibility of CARS spectroscopy of multiply charged ions in a laser plasma was established.
TL;DR: In this article, the influence of the composition of a mixture of working gases on the parameters of the active medium and output characteristics were determined under conditions typical of efficient operation of an electric-discharge CO laser.
Abstract: The influence of the composition of a mixture of working gases on the parameters of the active medium and output characteristics were determined under conditions typical of efficient operation of an electric-discharge CO laser. The experimental results were compared with theoretical calculations. A mechanism accounting for the influence of oxygen on the operation of a laser was identified.
TL;DR: In this paper, a BaTiO3 crystal characterized by gain values in the range 150 cm − 1.7 mm was used to demonstrate discriminatory phase self-conjugation of continuous radiation by spontaneous seeds.
Abstract: An experimental study was made of steady-state energy exchange between counterpropagating optical waves in a BaTiO3 crystal characterized by gain values in the range 150 cm − 1. Stimulated diffusion backscattering by spontaneous "seeds" was observed in a crystal 0.7 mm thick. The conditions for discriminatory phase self-conjugation of continuous radiation by this stimulated scattering mechanism were found theoretically. A steady-state discriminatory phase self-conjugation of He–Cd laser radiation was achieved for Gaussian and speckle pump beams.
TL;DR: In this article, an XeF laser with an active length of 170 cm and an exit aperture of 12 × 20 cm was used for a single-channel sectioned electrical discharge on the surface of polyethylene with a period-average deposited power density dP / dx ~ 41.6 MW/cm.
Abstract: An investigation was made of an XeF laser with an active length ~ 170 cm and an exit aperture of 12 × 20 cm. The optical pump source was a single-channel sectioned electrical discharge on the surface of polyethylene with a period-average deposited power density dP / dx ~ 41.6 MW/cm. The energy of the laser radiation generated as a result of the B–X transition (λ ≈ 351 nm) reached 70 J, whereas in the visible range the energy delivered by the C–A transition (λav = 480 nm) was 98 J.
TL;DR: In this paper, a dynamic distributedfeedback (DFB) rhodamine 6G dye laser under conditions of two-photon optical pumping by single fundamental-frequency pulses from an actively mode-locked YAG:Nd laser was used.
Abstract: Tunable generation of ultrashort pulses was achieved using a dynamic distributed-feedback (DFB) rhodamine 6G dye laser under conditions of two-photon optical pumping by single fundamental-frequency pulses from an actively mode-locked YAG:Nd laser At a dye concentration of 16 × 10 −2 mol/liter, the lasing threshold of the DFB laser was reached at a pump energy of ~ 6 mJ which corresponded to an intensity of ~ 77 GW/cm2 in the active zone The laser operated stably in the 580–606 nm wavelength range The width of the emission line was 01–05 nm A positive chirp of the lasing frequency was observed due to nonlinear modulation of the active medium refractive index in the high-intensity two-photon pump field
TL;DR: In this article, a jet system was used to generate singlet oxygen at a pressure 16 Torr and the concentration of the desired product was at least 60%. But the effective probability of trapping of chlorine molecules in a KOH-H2O2-H 2O solution decreased on increase in the concentration and was within the range 10 − 3 −10 − 2.
Abstract: A jet system was used to generate singlet oxygen at a pressure 16 Torr and the concentration of the desired product was at least 60%. The effective probability of trapping of chlorine molecules in a KOH–H2O2–H2O solution decreased on increase in the concentration of KOH and was within the range 10 − 3–10 − 2. The main factor limiting an increase in the O2(1Δ) pressure in such a jet generator was exhaustion of HO2− on the solution surface.
TL;DR: In this article, the first pulse performed the function of a vacuum pump and also generated a cloud of target particles, which increased the contrast of the spectral lines of the elements in the target as a result of breakdown in the field of the second pulse.
Abstract: Suppression of the emission of radiation of atmospheric gases in a laser plasma formed as a result of two-pulse irradiation of a target surface was due to a reduction in the gas density in the region of the interaction of the radiation with the surface. In accordance with this mechanism the first pulse performed the function of a vacuum pump and also generated a cloud of target particles, which increased the contrast of the spectral lines of the elements in the target as a result of breakdown in the field of the second pulse.
TL;DR: In this paper, a kinetic model for a Penning plasma Ne laser utilizing electron-beam-pumped He-Ne-Ar and Ne-H2 mixtures is constructed.
Abstract: A kinetic model is constructed for a Penning plasma Ne laser utilizing electron-beam-pumped He–Ne–Ar and Ne–H2 mixtures. Calculations are made of the plasma parameters and the lasing characteristics of the Ne yellow line (λ = 585.3 nm) in quasi-cw and pulsed pumping regimes. The calculated results agree well with the experimental data on lasing in a wide range of durations and densities of the pump current, and of mixture pressures and compositions.
TL;DR: In this article, a new type of intermode wave phase matching is proposed for the first time, which is used for the locking of cascade components of stimulated Brillouin scattering in a multimode fiber waveguide.
Abstract: Locking of cascade components of stimulated Brillouin scattering, excited in a multimode fiber waveguide, was achieved for the first time. It is postulated that a new type of intermode wave phase matching is responsible for such locking.
TL;DR: In this paper, an experimental investigation was made of fluctuations of the spectral distribution of the intensity in the wide-band spectrum of a ring cw traveling-wave dye laser, and the threshold of detection of an intracavity spectrometer, denned in terms of the absorption coefficient, was found to be governed by the quantum nature of the radiation used in the spectrometers and amounted to ~?3?X?10???17 cm???1 when the accumulation time was 20 s.
Abstract: An experimental investigation was made of fluctuations of the spectral distribution of the intensity in the wide-band spectrum of a ring cw traveling-wave dye laser. Allowance for the averaging within the limits of the instrumental function of a spectrometer was made by analyzing the noise power spectra obtained for the recorded intensity distributions. A good agreement with the theory was observed. The threshold of detection of an intracavity spectrometer, denned in terms of the absorption coefficient, was found to be governed by the quantum nature of the radiation used in the spectrometer and amounted to ~?3?X?10???17 cm???1 when the accumulation time was 20 s.
TL;DR: In this paper, a picosecond YAG:Nd3+ laser with passive mode locking and a negative feedback loop was constructed, and trains of between 7 and 5000 pulses of 20 ps duration were generated.
Abstract: A picosecond YAG:Nd3+ laser with passive mode locking and a negative feedback loop was constructed. Trains of between 7 and 5000 pulses of 20 ps duration were generated. Theoretical and experimental analyses of the operation of a solid-state picosecond laser with a negative feedback loop were made treating this laser as a discrete object of control. The theory made it possible to describe completely operation of the investigated laser. A laser with a negative feedback loop was found to behave in a complex manner and, under certain conditions, it demonstrated chaotic behavior. The criteria of stability of the operation of picosecond lasers with a negative feedback loop were established.
TL;DR: In this article, the influence of phase shift in a channel coupling two unstable-resonator CO2 lasers on the band width of stable phase locking of the laser fields was studied experimentally for the first time.
Abstract: The influence of a phase shift in a channel coupling two unstable-resonator CO2 lasers on the band width of stable phase locking of the laser fields was studied experimentally for the first time. The fraction of the radiation effecting the optical coupling was determined experimentally and found to vary in the range 10 − 3–10 − 2 for different coupling apertures. The maximum mismatch of the resonator lengths which did not disrupt the coherence amounted to ΔL≈λ / 20. A method developed for calculating the diffraction made it possible to determine numerically the stable phase locking range of the output radiation from two lasers with unstable resonators. The calculated and experimental parametric dependences of the phase-locking band width were in qualitative agreement.
TL;DR: In this paper, a study of selective reflection from an interface between a transparent dielectric and an absorbing gas as a function of the angle of incidence of radiation and of its polarization, and of the concentration of atoms in a cell was performed.
Abstract: Resonance lines of rubidium and cesium and injection lasers were used in a study of selective reflection from an interface between a transparent dielectric and an absorbing gas as a function of the angle of incidence of radiation and of its polarization, and of the concentration of atoms in a cell. Selective reflection resonances were observed against zero background when radiation was incident on the cell at the Brewster angle. The conditions for observation of selective frustrated total internal reflection (FTIR) were determined analytically and experimentally. The maximum reflection coefficient obtained was 95 ± 2%, which was 10 times greater than the nonresonant reflection coefficient. The spectral width of the region where FTIR was observed ranged from 0.1 to 1.5 cm − 1, depending on the concentration of atoms and the angle of incidence. The FTIR eifect was used to construct a selective component which made it possible to ensure narrow-band cw operation of an injection laser with an external resonator. Other potential applications of the FTIR effect in quantum electronics were also considered.
TL;DR: In this paper, the dependence of the contrast in the emission spectrum of a laser plasma on the degree of focusing of radiation from a neodymium laser on the surface of an aluminum target in the case of double-pulse irradiation was investigated.
Abstract: An experimental investigation was made of the dependence of the contrast in the emission spectrum of a laser plasma on the degree of focusing of radiation from a neodymium laser on the surface of an aluminum target in the case of double-pulse irradiation. For an interpulse interval of 25 μs there was a range of optimal radiation intensities of 0.5–2.5 GW/cm2 in which a fifteenfold increase in the contrast of the aluminum spectral lines was achieved. The principal mechanism for increasing the contrast and efficiency for transforming the laser radiation into radiation of the plasma spectral lines was found to be the flash absorption of the radiation of the second pulse in the leading edge of the gas–vapor cloud created on the target surface by the first pulse.
TL;DR: In this paper, an experimental investigation was made of the processes of interaction of radiation from an XeCl excimer laser (? = 308 nm,? = 20 ns) with aluminum.
Abstract: An experimental investigation was made of the processes of interaction of radiation from an XeCl excimer laser (? = 308 nm, ? = 20 ns) with aluminum. The threshold of formation of an erosion plasma in vacuum (q?* = 200 MW/cm2) was independent of the number N of the pulses. The threshold q?* in air depended strongly on N and could fall to 70 MW/cm2, due to the formation of a strongly absorbing layer on the target surface. The depth of the layer removed by radiation of intensity q???1 GW/cm2 could reach 1 ?m per pulse. The average optical thickness of a plasma created by one pulse was of the order of 0.3 at ? = 308 nm. Evaporation by XeCl laser radiation increased the aluminum absorptivity by a factor of 3?5. The erosion plasma temperature did not exceed 2 eV for q ? 1 GW/cm2. A general energy balance was determined for the laser radiation?target?plasma in vacuum.
TL;DR: In this article, the characteristics of radiation generated by a copper vapor laser operating in the superradiant regime and having a single convex mirror were investigated, and an LG-201 commercial sealed active element was used, with an experimental element having a discharge channel longer by a factor of 1.4.
Abstract: An investigation was made of the characteristics of radiation generated by a copper vapor laser operating in the superradiant regime and having a single convex mirror. An LG-201 commercial sealed active element was used, together with an experimental element having a discharge channel longer by a factor of 1.4. Highly stable radiation was obtained with characteristics which could be controlled by changing the mirror radius. For mirror radii two or three orders of magnitude smaller than the distance from the mirror to the exit aperture of the active element, the divergence angle of the beam was close to the diffraction limit. Average radiation power densities of 1?10 MW/cm2 could be achieved in a focal spot. This is more than two or three orders of magnitude higher than those obtained in a plane?plane resonator. The energy per pulse, the peak power, and the axis of the radiation pattern were several times more stable than for an unstable resonator, and the intensity distribution in the focal plane was also more uniform. These advantages should improve the quality of high-precision materials processing.
TL;DR: In this paper, a passively mode-locked YAG:Nd laser was built with a negative feedback loop based on a high-current photomultiplier and the duration of these trains was several tens of microseconds.
Abstract: A passively mode-locked YAG:Nd laser was built. It was provided with a negative feedback loop based on a high-current photomultiplier. Trains of picosecond pulses were generated and the duration of these trains was several tens of microseconds. When steady-state operation was reached, the feedback loop was disconnected and a short train of picosecond pulses with an overall duration of ~?100 ns and an energy 1.5 mJ was generated. The energy stability of a second harmonic generated by such a short train was ? 1.5% when the efficiency of conversion to the second harmonic was low.
TL;DR: In this paper, the feasibility of suppression of stimulated Brillouin backscattering by phase modulation of the pump radiation and/or a longitudinal gradient of the frequency shift is discussed.
Abstract: The feasibility of suppression of stimulated Brillouin backscattering by phase modulation of the pump radiation and/or a longitudinal gradient of the Brillouin frequency shift is discussed. In both cases, the signal amplified by stimulated Brillouin scattering (STBS) in one part of the medium is out of resonance with the pump radiation in another part of the medium. A suitable theory of STBS is constructed for the transient regime when STBS is suppressed less efficiently.