Search

A self-consistent method is used for the first time to calculate the characteristics of ring lasers with intracavity acousto-optical interference components. The results obtained by this method are shown to differ considerably from those obtained traditional methods. The traditional methods for the calculation of losses, phase shifts, and phase and amplitude anisotropies of such acousto-optical components cannot be used to determine the output parameters of typical solid-state ring lasers because the frequency dispersion of such components is exceptionally high.

A study was made of the characteristics of the formation, in the absence of seed radiation, of a χ(2) grating with an efficiency of 4% in Ge—Er optical fibres. In a wide dynamic range of the χ(2)-grating amplitude, there was a direct relationship between the growth rate of the grating and the intensity of the UV third and fourth harmonics of a neodymium laser generated by the cubic χ(3) nonlinearity inside a fibre. The experimentally determined characteristics of the growth and saturation stages of the formation of a grating were in agreement with the proposed physical interpretation based on a model of a coherent photocurrent and on the assumption that the UV harmonic radiation participates in the photoionisation of donor and acceptor centres.

The spectral dependence of photoinduced optical losses after chi((2)) writing have been obtained in Sm- and Er-doped fibers. The results show that Sm(2+) and Er(2+) can be a source of photoelectrons during fiber preparation.

An investigation is reported of the dependence of the frequency of low-frequency relaxation oscillations of the radiation power of solid-state ring lasers on the nature of the polarisation of the counterpropagating optical waves and on the ring cavity parameters. It is shown that the maximum frequency of antiphase low-frequency oscillations corresponds to the linear collinearly oriented polarisations of the counterpropagating waves. An increase in the ellipticity of the counterpropagating waves reduces the frequency of the antiphase oscillations and this frequency tends to zero for orthogonal circular polarisations of these waves.

An experimental investigation was made of a mode-locked garnet laser with intracavity second-harmonic generation. The peak power of the ultrashort pulses was improved appreciably and the intracavity second-harmonic generation efficiency was enhanced by increasing the effective resonator length using an afocal optical delay line.

Laser beams with helical wavefront dislocations and their applications in the diagnostical and metrological systemsT.I.Arsenyan, N.N.Fedotov, L.S.Kornienko, P.V.Korolenko, E.A.Kulyagina, G.V.PetrovaMoscow State University, Faculty ofPhysics, Chair of Optics and Spectroscopy, Lenin Hills, Moscow 1 19899, RussiaABSTRACTProperties and practical applications of the light beams with helical dislocations (HD) of wavefront in metrological systemsare considered on the basis of experiments with gas lasers and numerical ones. It is shown, that the super stable lasers-heterodynes with high quality of out coming radiation can be created using lasers with inner-resonator helical fiel&;.Conditions of HD appearance in laser beams propagating through the turbulent atmosphere are determined. Method ofdefinition of atmospheric turbulence degree based on HD number counting is suggested.

Optical fibers are widely used in modern nonlinear optics and quantum electronics for the transformation and generation of coherent radiation. They operate either as nonlinear or linear waveguide elements. The following two types of optical schemes are used: (i) those without a resonator, with useful effect, i.e., the transformation of radiation achieved at a single pass along the fiber; (ii) those with a resonator that ensures recirculation of radiation and accumulation of the useful effect. Case ii is actually a laser of a special type —a fiber laser.

Valerian Grigor'evich Shevchenko (Obituary) Yu V Galaktionov, Mikhail V Danilov, Vladimir S Imshennik et al. Anatoli Aleksandrovich Vlasov (obituary) I P Bazarov, N N Bogolyubov, Boris B Kadomtsev et al. Physics and astronomy at Moscow University (On theUniversity's 225th anniversary) B I Spasski, L V Levshin and V A Krasil'nikov Configurational splitting of the giant dipole resonance in atomic nuclei B S Ishkhanov, I M Kapitonov, Vladimir G Neudachin et al. German Stepanovich Zhdanov (Obituary) N B Brandt, B K Vanshten, A S Ilyushin et al. Yuri Mikhalovich Shirokov (Obituary) N N Bogolyubov, S N Vernov, Vasilii S Vladimirov et al. Dmitri Vladimirovich Skobel'tsyn (Obituary) A M Baldin, N G Basov, Vitalii L Ginzburg et al. Igor' Borisovich Teplov (Obituary)

Photoinduced second-harmonic generation in silica fibers doped with Er(3+), Sm(3+), and Tb(3+) has been investigated. Er(3+)-doped fibers have been found to tune a chi((2)) grating easily to the mode structure of the laser radiation, whereas Sm(3+)-doped fibers have been found to possess the greatest resistance to chi((2)) grating erasure by radiation at 532 nm. From the beginning of the preparation processes, the third harmonic at 355 nm is registered in all the fibers.

Absorption coefficients measured at 5 to 6 and 10.6 pm by CO- and CO2-laser calorimetry of TICl, KRS-6 (TICl-TlBr), TlBr, and KRS-5 (TlBr-TlI) crystals are found to increase upon irradiation with 60Co γ-rays. It is found that the radiation resistance of the crystals substantially increases with the halogen number. The dose dependence of γ-induced absorption spectra from 0.36 to 15 μm is measured for TlCl. The results of the measurements are explained by the formation of Tl aggregate centres. [Russian Text Ignored].

A method was developed for the electrovacuum fabrication of very pure quartz glass completely free of hydroxyl ions. The optical losses of this glass in the 0.6–1.1 μ range were found to be 10 dB/km, which made the glass suitable for fiber optics applications. A study was made of the increase in the optical losses under the action of γ rays. The resistance of the new glass to the effect of small (104–105 rad) γ-ray doses was inferior to that of the KSG glass but, at high doses (108 rad), the resistance was comparable for the two glasses. It was concluded that the resistance of the new glass to γ-ray effects was limited by the presence of modifier ions in the glass network.

A review is given of the radiation-optical properties of glass fiber-optic waveguides. Particular attention is paid to an analysis of radiation-induced absorption in multimode fiber-optic waveguides having pure and doped quartz glass cores. Dependences of the induced absorption on the dose, power, and type of radiation, on the temperature, the concentration of dopants and hydroxyl groups in the core, and on the wavelength and power of the probe radiation are discussed. An analysis is made of the kinetic curves of the changes in the induced absorption both during and after exposure to the radiation. Some models describing the effects of radiation bleaching and optical bleaching are analyzed. The propagation of a bleaching pulse through a radiation-darkened waveguide is examined.

An investigation was made of the influence of temperature and optical power level on the magnitude of induced absorption in fiber-optic waveguides made of pure quartz glass. It was found that coupling additional bleaching radiation into a waveguide at a power level of ~10−6 W decreased its induced absorption by several orders of magnitude. Previously unknown quartz-glass induced-absorption bands were discovered and their optical and thermal bleaching investigated.

Theoretical and experimental investigations were made of the influence of a magnetooptic feedback loop creating a difference between the losses for opposite waves, proportional to the difference between their intensities, on the amplitude and frequency characteristics of a rotating solidstate ring laser with a homogeneously broadened luminescence line of the active substance. Analytic solutions were obtained for the description of possible lasing regimes and a study was made of their stability for arbitrary values of the difference between the frequencies of the opposite waves. It was found that a feedback loop with a large transfer coefficient was capable of ensuring stable and simultaneous lasing under several regimes. It was established experimentally that optimization of the parameters of the loop in a rotating YAG:Nd3+ ring laser resulted in stabilization of the beat regime and expanded significantly the range of existence of this regime. The inertia of the feedback loop observed on increase of its transfer coefficient resulted in an instability of bidirectional lasing, giving rise to antiphase oscillations of the intensities of the opposite waves. A study was made of the transient processes which occurred as a result of abrupt changes in the signal in the feedback loop. The results of theoretical investigations were in good agreement with the experiments.

Theoretical and experimental investigations were made of the possibility of increasing the efficiency of intracavity modulation and stabilization of the radiation emitted from ring lasers by utilization of the competition between counterpropagating waves. It was established that in the case of solid-state ring lasers one can switch rapidly the direction of counterpropagating waves both in the case of forced mode locking and in the case of single-mode emission without spike transient processes at a relaxation frequency typical of solid-state lasers. An analysis was made of the conditions for significant reduction of the switching time and a method is suggested for achieving this by simultaneous modulation of the amplitude nonreciprocity and of the coupling between counterpropagating waves. It is shown that highly stable unidirectional single-mode operation of a solid-state ring laser can be achieved as a result of weak modulation of the resonator perimeter. Various time dependences of the intensities of counterpropagating waves and stabilization of bidirectional operation of a solid-state ring laser were achieved using a magnetooptic feedback loop.

Principles of design and construction are described for modern quantum amplifiers (masers), which are the most sensitive input devices of ultrahigh-frequency radio receiving systems. Data are given on the characteristics of paramagnetic crystals for quantum amplifiers (QA) and on the attained QA parameters. Problems are discussed of application of QA in radio astronomy (cosmic radiospectroscopy, radar observation of planets, very-long-baseline radiointerferometry, etc.) and in long-range space radio communication systems.

Results are presented of numerical experiments to investigate the dynamics of ultrashort light pulse generation in a laser with a bleachable filter when a Raman-active medium having a wide gain profile is introduced into the laser resonator. It is found that intracavity Raman frequency conversion of ultrashort pulses in a master oscillator opens up prospects for achieving limiting durations determined by the reciprocal width of the gain profile of the active medium and by the width of the spontaneous Raman scattering line.

Measurements were made of the Einstein coefficients of the spontaneous transitions from the 4F3/2 metastable level of Nd3+ to all the levels of the 4I ground-state multiple! occurring in several silicate and phosphate glasses. The cross sections of the 4F3/2→4I11/2 laser transition were determined. It was demonstrated that the spectroscopic methods suggested in the literature for the determination of these quantities could give rise to basic and uncontrollable errors.

An experimental investigation was made of a cw YAG:Nd3+ solid-state ring laser with a nonstationary resonator. New lasing regimes and competing effects of interaction between opposite waves were observed. In particular, under conditions of low-frequency (f~100 Hz) vibrations of one of the ring resonator mirrors, the following regimes were observed: regimes with cophasal or antiphase modulation of the opposite wave intensities, regimes with different frequencies and different modulation in the opposite directions, regimes with variable-frequency antiphase oscillations of the opposite wave intensities, regimes with trains of cophasal pulses, and kinematic mode-locking regimes.

A single pulse from a neodymium laser is used to initial electrical breakdown in glasses which accumulate and preserve a space charge induced by a beam of rapid monoenergetic electrons. Laser initiation permits use of high-speed recording apparatus and study of the initial stage of electrical breakdown in the charged glasses. A time delay in electrical breakdown relative to the initiating optical radiation was observed and measured, corresponding to the time of formation of a conductive channel between the region of space-charge localization and the specimen surface. Growth rates of the conductive channel are determined for surface and volume initiation, and possible mechanisms of laser initiation are considered.

A study was made of the influence of laser light on radiation color centers in glass fiber waveguides of the SiO2–SiO2:B2O3 type. The induced-absorption spectra were determined in the wavelength range 300–1900 nm for fibers subjected to γ-ray doses from 300 to 104 rad at irradiation temperatures 77 and 300 K. Eight types of radiation color centers were identified and the induced-absorption spectra of the waveguides were almost entirely due to these color centers. The centers differed in respect of the stability when subjected to laser light and temperature variations. Infrared absorption appeared when the induced-absorption band at 340 nm was suppressed by λ = 337 nm laser light and then restored at room temperature.

An experimental determination was made of the threshold temperatures for the excitation of optical discharges in silicate glasses under the action of millisecond laser pulses. At normal pressure the discharges on glass surfaces appeared at a temperature of ~ 2000 K. In the interior of the glasses, where the pressure as a result of local heating increased to ~ 104 atm, the discharges appeared at ~ 2500 K. A theoretical analysis was made of spontaneous decomposition of the main glass-forming oxide (silica) and it was found that the proposed model describes satisfactorily the pressure dependence of the threshold temperature. A quantitative agreement was established between the calculated thermal characteristics of the decomposition process and the experimentally determined threshold temperatures for the onset of optical discharges.

A quantitative simulation in the cluster approximation is made of an autolocalized hole in the amorphous SiO2 network. A model is suggested in which the thermal excitation of holes from Anderson localized states of the top of the silica valence band above the mobility edge corresponds to the thermally stimulated luminescence peak at 125 K, and the analogous optical transition — the radiation-induced low-temperature IR-absorption. The position and form both, of the peak and absorption band and their thermo- and photostability are explained. [Russian Text Ignored].

An investigation was made of the damage threshold, partial melting, and bleaching of radiation-colored K-8 glass as a function of γ-ray dose. The threshold temperatures were estimated and it was found that the residual absorption coefficient of glass was constant right up to power densities at which bulk damage was observed. Two types of radiation defects were found in K-8 glass and these defects were responsible for the absorption at γ = 1.06 μ.

A theoretical study is made of kinematic mode locking in a laser with a homogeneously broadened luminescence line, which occurs during translational motion of one of the mirrors along the resonator axis. The problem is reduced to a system of algebraic equations, the solutions of which determine the quasisteady parameters of a near-Gaussian weakly asymmetric pulse traveling in the resonator.

An experimental investigation was made of unidirectional and bidirectional emission from a ring laser having a resonator perimeter that varied periodically at a frequency of 250 Hz and an amplitude of up to 250μ. It was found that the most favorable conditions for mode locking in this laser occur when the perimeter is varied by moving one of the resonator mirrors. It was established by means of calculations that there is minimal coupling whereby the mode locking stability is ensured in the bidirectional emission regime.

An experimental investigation was made of the influence of the diffraction acoustic feedback on the stimulated emission from a YAG:Nd3 solid-state ring laser with forced acoustooptic mode locking. The feedback was created by directing beams diffracted in an acoustooptic modulator back to the ring laser resonator. A study was made of systems with a single reversing mirror and with an additional linear or ring resonator for the diffracted beams. In all cases this feedback broadened considerably the mode-locking band. It was possible to modulate in different ways the intensities of the opposite waves in the ring laser by sweeping the ultrasonic wave frequency inside the mode-locking band. In particular, the direction of the radiation emitted by the ring laser could be switched without low-frequency transients.

It is shown experimentally that induced absorption in a fiber-optic waveguide with a pure quartz glass core can be bleached within ~100μsec by optical radiation pulses of ~10−5 J energy.

An experimental study was made of the competitive interactions of opposite light waves in a YAG:Nd3+ ring laser with acousto-optic mode locking. These effects were investigated with the laser at rest and rotating. A study was made of the dependence of suppression of one of the opposite waves on the detuning of the modulation frequency from the intermode value, on the difference between the resonator frequencies due to rotation, and on the position and orientation of the acousto-optic modulator. It was found that the competition between the opposite waves in the case of forced mode locking could be weaker or stronger than in the case of free oscillations. Moreover, in the case of a solid-state ring laser with a homogeneously broadened luminescence line of the active substance one could realize bidirectional or unidirectional mode locking. Different forms of modulation of the intensities of the opposite waves were possible under forced mode-locking conditions when the ultrasonic frequency was scanned.

An experimental study was made of the mode-locking regime in a cw YAG:Nd3+ laser. It was found that an increase of the detuning between the modulation frequency of the phase and the frequency of intermode beats altered the structure of ultrashort pulses. A study of an active-passive mode-locking method revealed the existence of two symmetrically located regions of detuning of the modulation frequency within which stable generation of ultrashort pulses free of structure was possible.

A report is given of an experimental investigation of a garnet laser with an optical-fiber resonator. It was established that intense Raman emission appears at wavelengths of 1.12 and 1.18 μ in a laser of this type, in addition to emission at the wavelength 1.06 μ. The energy characteristics and dynamics of the radiation at the fundamental and Raman frequencies were investigated.

The first results are reported of forced phase mode locking in a cw YAG:Nd3+ ring laser. The locking was produced by inserting an electrooptic LiNbO3 phase modulator in the resonator. The modulator varied the resonator perimeter at the intermode beat frequency. The time, spectral, and frequency characteristics of the laser were investigated in the phase mode locking regime. The width of the locking band was determined. In the phase locking regime the competition between the opposite waves was much weaker and there was also a reduction in the locking range when the ring laser was rotated. Moreover, spontaneous axial mode locking was observed in the absence of periodic variations of the resonator parameters.

A simple method is proposed and realized for making high resolution fiber-optic Fabry–Perot interferometers having a spectral scanning period of the order of tens of microseconds.

A method for the generation of an ultrashort Raman pulse train with peak power considerably in excess of the pumping one is proposed and theoretically developed. It is shown that it can be used for obtaining tunable picosecond pulses in Raman fiber laser.

An investigation was made of the influence of single-mode radiation from an injection laser on the magnetic resonance signal as a function of the laser radiation frequency. It was found that the amplitude, phase, and rate of decay of the free precession signal depended on the tuning of the laser radiation frequency within the Doppler profile of the line representing the hyperfine levels of the ground state of cesium.

The phenomena of optical bistability, hysteresis and memory under the interaction of oppositely directed (OD) light waves in a CW YAG:Nd3+ solid state ring laser (SRL) have been experimentally discovered. The possibilities of spontaneous or forced (with modulated SRL parameters) commutation of the radiation direction without transients at the relaxation frequency (typical for solid state lasers) have been established both in the single-mode and in the mode-locking regimes with various feedback circuits. The mode-locking band was found to be substantially broadened by more than an order of magnitude when OD light waves primarily diffracted on a standing ultrasonic wave were returned into the acousto-optical modulator. With such acousto-optical feedback the mode-locking regime has been obtained using a modulator on a running ultrasonic wave.

The EPR spectra of PO 4 2− and PO 3 2− and atomic hydrogen were observed in γ-irradiated (Li-TRx-La1−x) — phosphate glasses, where TR = Nd, Sm, Er. Using the obtained data on the atomic hydrogen EPR spectrum the estimation of the OH− group concentration was made for these glasses.

It is found experimentally that the competitive interaction of the oppositely directed (OD) light waves in YAG:Nd3+ and ruby solid-state ring lasers OIRL) can be significantly reduced due to nonlinear optical effects (second harmonic generation, stimulated Raman scattering, resonant absorption) since the nonlinear losses for the wave of lower intensity are lower. It was established that in the SRL with a resonantly absorbing medium the spatially inhomogeneous burning-out and the slowness of the relaxation of the inverted population in the solid-state active medium may result in strong phase nonreciprocity due to the frequency shift of the OD waves after their reflection from the moving lattice of the inverted population. The beat frequency strongly depends on detuning between the gain and absorption lines and may be more than two orders of magnitude less in comparison with the resonator frequency difference in the rotating SRL. The possibility has been shown of active stabilization of the bidirectional generation in the beat regime using the nonreciprocal amplitude Faraday element controlled by the external feedback circuit via the difference of the OD waves intensities.

Reversible optical bleaching of the induced absorption was observed and investigated in the range 0.5–1.3 μ for γ-irradiated glass fiber waveguides. The bleaching was produced by He-Ne laser radiation (γ = 0.63 μ). The effect was associated with an induced absorption band characterized by-a maximum in the range ~0.9 μ.

An investigation was made of the profile of the hyperfine component of the cesium line observed using a cw semiconductor laser. It was found that the profiles of the absorption and luminescence signals, their widths, amplitudes, and the positions of the maximum depend strongly on the relaxation time of the active medium, laser radiation intensity, and rate and direction of passage of the frequency through resonance.

Passive mode locking was achieved for the first time in a cw solid-state YAG:Nd3+ laser using a filter based on the use of an LiF crystal with color centers as the saturable absorber. A study was made of the effect of the filter density on the lasing dynamics.

An investigation was made of the radiation-optical stability of SiO2:GeO2–SiO2 and SiO2–SiO2:B2O3 glassfiber waveguides. The induced absorption spectra in the 0.45–1.75 μ wavelength range were obtained by altering the gamma-radiation dose between 103 and 108 rad. An investigation was made of the growth kinetics of the induced absorption of the waveguides during gamma irradiation and of the induced absorption decay kinetics after irradiation.

Theoretical and experimental investigations were made of the properties of a solid-state ring laser in the case of kinematic modulation of the resonator length. It is shown that the observed characteristics can be explained only if we allow for the combined influence of the variable-sign frequency offset and modulation of the coupling between the opposite waves.