Table of contents

An investigation was made of the influence of active mode locking on the stability of generation of giant pulses at different Q-switching frequencies F. In the absence of locking near chaotic operation regions there were two lasing regimes with spectra characterized by very different widths. The change from one regime to another occurred in a random manner. The duration of the existence of a particular regime depended on F and was several orders of magnitude higher than 1/F.

An experimental investigation was made of a compact gadolinium scandium gallium garnet (GSGG) laser activated with Cr³⁺ and Nd³⁺, and containing phototropic centers. The active element of this laser performed the function of a passive Q switch. Lasers of this kind were demonstrated to be capable of generating nanosecond pulses with an energy of up to 5 mJ per pulse.

A study was made of the time characteristics of a distributed-feedback (DFB) dye laser pumped by single pulses from a picosecond YAG: Nd³⁺ laser. The duration and delay of the pulses generated by the DFB laser depended on the pump energy and on the DFB laser emission wavelength. When the pump energy exceeded the threshold by a factor of 3–4, the stability of the time characteristics of the DFB laser was 15–20% in the case of a slight (10–15 nm) detuning of the emission wavelength from the center of the line profile.

Gaseous plasma was used to control the characteristics of the output radiation of a GSGG:Cr³⁺ laser. The use of a plasma medium made it possible to alter the spectral radiation power and the duration of the pulses by several orders of magnitude.

The rotational relaxation time and its spectral dependence were determined for oxazine 17 in hydrogen-containing alcohols and it was found that the governing factor was an intermolecular hydrogen bond with the solvent. A strong reduction in the strength of this intermolecular interaction in deuterated alcohols was accompanied by a short-wavelength shift of the fluorescence spectrum and by an increase in its quantum efficiency.

It is shown experimentally that the divergence of radiation from a laser with a retroreflecting mirror may be reduced considerably (compared with the diffraction limit) by one retromirror component because of phase self-locking of the mirror components.

Stimulated emission from color centers in an Al₂O₃:Mg crystal was achieved in the range 500–590 nm. Spectroscopic information on the active centers was obtained.

A high-efficiency Q-switched GSGG:Cr:Nd laser (∼3%) is described.

An investigation was made of a YAG:Nd³⁺ crystal ring laser with an acoustooptic phase-nonreciprocal element. This element provided effective control of lasing kinetics. The conditions for ensuring unidirectional single-frequency emission with the aid of this element were determined. It was found that an ML-202 acoustooptic mode locking device introduced a phase nonreciprocity between the opposite waves as a result of which bidirectional emission in this solid-state ring laser with longitudinal mode locking became possible for certain angular positions of ML-202. The conditions were identified for unidirectional emission in the case of acoustooptic locking of longitudinal modes.

Coherent pumping of a titanium-activated chrysoberyl laser, by the second harmonic of a continuously pumped YAG:Nd laser operating in the Q-switched regime at a pulse repetition frequency 3–15 kHz, made it possible to achieve a conversion efficiency of ∼5% and tuning of the emission wavelength in the range 0.73–0.95 µ. It was found experimentally that the lifetime of an excited state of the Ti³⁺ ions decreased on increase in temperature from 4.9 µsec at 300 K to 0.2 µsec at 500 K.

An yttrium scandium gallium garnet crystal activated with chromium, thulium, and holmium ions was investigated. A differential lasing efficiency of 3.1% was obtained (for the ⁵I₇ → ⁵I₈ transition in the Ho³⁺ ions) at room temperature and the emission wavelength was 2.088 µ.

Possible methods of achieving pulse-periodic operation of an oxygen–iodine chemical laser (OICL) are indicated. The energy characteristics and efficiency of the pulse-periodic regime are improved substantially if atomic iodine is prepared rapidly in a singlet oxygen medium. This can be done by flash ultraviolet photolysis of iodides. An analysis is made of a system for generation of single nanosecond pulses in an OICL, incorporating a multipass ring amplifier. Coherent amplification conditions can be achieved in this system and the energy stored in the upper level of the iodine atom can be extracted with a 95% efficiency. Estimates show it is realistic to obtain an energy of around 100 kJ, so that the proposed system is potentially useful for laser fusion applications.

An experimental investigation was made of the kinetics of the output energy at different pulse repetition frequencies in a pulse-periodic XeCl excimer laser using He and Ne as the buffer gas component. It was found that the homogeneity of the discharge in the pulse-periodic regime was conserved more readily in an Ne gas mixture than in an He mixture. The highest average power achieved so far for electric-discharge pulse-periodic excimer lasers, ∼400 W, was obtained for a two-module XeCl excimer laser utilizing an HCl:Xe:Ne = 1:10:1200 gas mixture. It was established that a reduction in the average output power and the service life of the laser could be due to the formation, in the laser channel, of fine particles which scattered the radiation and promoted formation of an absorbing film on the resonator mirrors.

An analysis was made of the design of a cw HF laser utilizing a chain reaction with a thermal branching mechanism and suitable molecules are proposed. This analysis made it possible to select the shape of the laser chamber needed to prevent a thermal crisis of the supersonic stream in this laser.

Investigations were made of the pump power density and of the emission characteristics of an XeCl laser having an active volume of up to 30 liters. Attention was paid to the inhomogeneity of the excitation of the active region. For electron beam current densities in the range 5–15 A/cm², the halogen content of the mixture was a function of the pump power density. The gain (3 m⁻¹) and the unsaturated absorption (0.3 m⁻¹) were determined. The specific laser output energy was 4 J/liter and the efficiency was ∼2%.

An investigation was made of the conditions under which control was possible of a narrowband XeCl laser with injection locking when the duration of the output pulses of this laser was 60 nsec and the duration of an external signal was 15 nsec. A definition of the efficiency of injection locking of an XeCl laser was introduced. It was found that this efficiency reached 95% when the intensity of the external control signal was ~2 W/cm², but the efficiency fell to zero when the intensity was 7 mW/cm². The output power of the laser exceeded 100 kW and the divergence was within 0.15 mrad when the spectral line width was 5 pm.

An experimental investigation was made of a supersonic mixing CO chemical laser with an equilibrium source of CS and S, based on thermal dissociation of carbon disulfide molecules in nitrogen heated to a high temperature using a pulsed arc plasmatron. An output power of ∼730 W and a specific output energy of ∼13 J/g were obtained.

An experimental investigation was made of fluctuations in the output power of a CO₂ laser when laser radiation reflected from a target was returned to the unstable resonator. It was found that a small fraction of the laser radiation (less than 10⁻⁴) reflected by an optical discharge plasma, whose density was much lower than the critical density, led to strong fluctuations (of the order of 100%) in the laser emission. A theoretical model predicting the possibility of the appearance of the experimentally observed fluctuations in the laser emission was proposed.

It is shown that the 3¹D–2¹P transition in helium-like ions is of interest for the amplification of light of wavelengths λ < 50 nm. An analytic formula is derived for the gain due to this transition. An analysis is made of the time dependence of the gain in the model of consecutive recombination during vacuum expansion of an initially completely ionized plasma filament. An allowance is made for the recombination heating of electrons, reabsorption due to the 2¹P–1¹S₀ radiative transition, and changes in the ion composition of the plasma during its expansion. It is shown that the maximum value of the gain for the C V ion [λ (3¹D–2¹P) = 26.7 nm] is ∼1 cm⁻¹.

The results are given of numerical calculations of the characteristics of pulsed copper vapor amplifiers. These are compared with the systematized and generalized known experimental data. General relationships governing the saturation in amplifiers of this type are determined.

Experimental and theoretical investigations were made of the characteristics of an uncooled electron-beam-controlled atmospheric-pressure laser utilizing simultaneously vibrational–rotational transitions in the CO and CO₂ molecules. A theoretical model was developed on the basis of a self-consistent solution of the equations of vibrational kinetics and the Boltzmann equation for the electron energy distribution function. A good agreement between the experimental and calculated results was obtained. An investigation was made of the problem of control of the emission spectrum. It was found theoretically that the overall efficiency could reach ∼20% (in the case of approximately the same efficiencies in the spectral ranges 5.5 and 10.6 µ) if a laser of this type were cooled to 200 K.

A numerical analysis is made of the transport of electrons in matter in the presence of magnetic fields. It is shown that the energy absorbed in the interior of a gas laser increases approximately twofold on application of a magnetic field. The results are given of a calculation dealing with electron-beam pumping of an amplifier with a large transverse cross section.

An experimental investigation was made of lasing in neon at λ = 540.1 and 585.3 nm when this gas was pumped by a transverse discharge. At λ = 540.1 nm the duration of the laser pulses was 35 nsec. The addition of argon to an He–Ne–H₂ mixture pumped by a self-sustained discharge increased the duration of the output pulses at λ = 585.3 nm.

New mechanisms of the cubic nonlinearity of absorbing liquid crystals are proposed. These mechanisms can result in parametric amplification in the case of frequency-degenerate interaction of waves. Amplification is based on the dependence of the pitch of a helix of a cholesteric liquid crystal on temperature or on the concentration of an isomer which is formed as a result of absorption of incident radiation. The possibility of amplification as a result of a gyrothermal effect in nematic liquid crystals is considered. Typical pump intensities required for the observation of these effects amount to a few watts per square centimeter.

A self-pumped mirror was implemented experimentally for CO₂ laser radiation generated by a four-wave interaction with feedback in CCl₄ and SF₆. The lowest threshold energy of the input signal was ∼8 mJ for CCl₄ and ∼2 mJ for SF₆. The energy reflection coefficient was 5 for CCl₄ and 11 for SF₆. The maximum energy of the output radiation exceeded 0.2 J.

The possibilities of compensating random small-scale phase distortions in a linear wavefront reversal system utilizing a spatial phase filter were analyzed by numerical methods. It was found that for an appropriate choice of the parameters of the system it is possible to compensate effectively such distortions in the variance range 0.1–1.3 rad². The improvement in the axial light intensity depends on the spatial spectrum of the distortions and can be as high as a factor of ten. The permissible misalignments of the system are estimated and recommendations are given on the choice of its parameters.

An experimental investigation was made of the efficiency of reflection and of the precision of wavefront reversal in the case of saturation of stimulated Brillouin scattering (STBS) competing with other nonlinear processes. It was found that the maximum pump power reaching STBS mirrors made of glasses and quartz was limited by the breakdown of the scattering medium and in some cases such breakdown occurred only in the scattering saturation regime. A study was made of an STBS oscillator–amplifier system in which such breakdown was suppressed so that the pump energy could be increased. Methods for widening the dynamic range of STBS mirrors were investigated.

The dependence of the optimal length of a nonlinear wave interaction region on the angle of birefringence in the direction of phase matching is determined for an optical parametric oscillator utilizing an anisotropic uniaxial crystal with a quadratic nonlinearity. The analysis is made assuming a strong feedback at both parametric frequencies and the optimal focusing of the interacting waves.

A theoretical analysis is made of the space and time structure of optical pulses formed by opposed stimulated Brillouin scattering (STBS) of focused laser beams allowing for an inhomogeneous transverse intensity distribution. It is shown that the laser pulses obtained under conditions of maximum compression and efficient STBS reflection have a complex space and time intensity distribution. The time structure of the reflected pulses obtained in the case of a large focusing angle is due to smoothing of a quasiperiodic time substructure of the Stokes pulse because of a transverse redistribution of the intensities of the interacting beams. Calculations are made of the coefficients of reflection and STBS compression as a function of the excess of the pump intensity above the threshold and of the focusing angle. Good agreement with experiments is found.

A theoretical investigation is reported of the Raman scattering and fluorescence (doublet) spectra of three-level quantum systems subjected to a strong laser field reducing broadening of the spectral lines caused by adiabatic perturbations (elastic collisions). The dependences of the frequency shifts, widths, and integrated intensities of the spectral components of the doublet on the intensity and frequency of the laser field are derived allowing for the influence of this field on the collision dynamics.

An investigation was made of the tuning of the Stokes and anti-Stokes components of stimulated four-photon processes in germanium dioxide-silicate fiber waveguides when the wavelength of one of the biharmonic pumping waves and the core radius were altered. An analysis was made of the propagation of the components formed by such four-photon processes in various combinations of the first two LP waveguide modes. The ranges of the waveguide parameters and pump wavelengths satisfying the condition of phase matching of the modes participating in the stimulated four-photon processes were determined. Feasibility of phase matching in single-mode waveguides at pump wavelengths very different from the wavelength at the maximum of the material dispersion was demonstrated. Variation of the wavelength of one of the pump waves within intervals typical of tunable lasers varied the wavelengths of the Stokes and anti-Stokes components of the investigated four-photon processes in wide spectral ranges in the visible and near infrared.

A theoretical analysis is made of the process of formation of periodic structures of evaporation damage by interaction of the surface of a metal or a semiconductor with laser radiation. The nonlinear stage of the process is considered. It is shown that additional periodic structures may appear during this stage. The conditions under which this happens are identified and the growth increments are calculated. The discussion applies to the majority of the experimentally observed structures: the appearance of new structures is predicted and conditions favoring such structures are identified.

An analysis was made of the kinetics of the appearance of a plasma near the surface of a heated body. It was assumed that during the heating process the surface temperature did not exceed the boiling (sublimation) point at a given external pressure and there was no intense evaporation. A quasisteady-state breakdown model was developed for the case when the characteristic time for the change in the vapor concentration due to surface heating was long compared with the characteristic time for the establishment of the spatial distribution of the vapor. It was found that the breakdown of the vapor and of the ambient gas occurred at different laser radiation intensities while the dependences of the principal parameters of the surface laser plasma on the radiation intensity were of a hysteretic nature. An analysis was also made of the case when the vapor concentration due to the heating varied rapidly compared with the characteristic time for the vapor distribution to be established. It was found that in this case the breakdown of the vapor of the target material could be accompanied by the breakdown of the ambient gas. A comparison was made with experimental data.

A theory of saturated absorption resonances is developed for the transit range of pressures of an absorbing gas with an arbitrary degree of saturation. The rate equation approximation is used to obtain expressions for the absorption coefficient in the cases of one traveling wave, weak and strong opposite waves, and a standing wave with a rectangular radial distribution of the intensity. An analytic study is made of the behavior of resonance widths when the saturating field intensities are varied and it is shown that, in particular, at relatively low densities the widths are proportional to the fourth root of the intensity.

A study was made of the dynamics and mechanisms of fast bimolecular processes of formation of intermolecular exciplexes and free radicals as a result of laser photolysis of molecules. Luminescence was observed and lasing was achieved in the case of aromatic free radicals in the gaseous phase.

A determination was made of the limiting value of the gain governed by the resonance properties of laser pump systems of the optical boiler type with planar YAG:Nd³⁺ active elements. A study was made of the influence of the properties of the discharge plasma, reflector, geometry of the system, and pump energy on such active elements.

Prospects of development of a holographic system for recording and reproduction of digital signals are considered and basic principles of the design of these systems are discussed. Devices for recording and reproduction are described and some results of experimental investigations of these devices are reported. Possible applications are identified on the basis of the parameters already achieved.

The method of coherent anti-Stokes Raman scattering (CARS) was used to probe the plasma of an optical spark formed on the surface of a steel target. Five strong resonances due to transitions between excited states of Fe I atoms were recorded in the CARS spectrum. A study was made of the kinetics and polarization properties of the scattered anti-Stokes radiation. The CARS method is recommended for the study of the plasma formed as a result of optical breakdown at solid targets because it can provide a universal means for the analysis of the chemical composition of the targets.

A nonlinear correction to the probability of a transition in atoms interacting resonantly with the field of a standing wave, averaged over the atomic velocities, is shown to have logarithmic divergences responsible for the slow atom effect. This effect and the resultant narrowing of Doppler-free lines of the lamb dip type are found to occur both in a gas and in an atomic beam.

An experimental determination was made of the coefficient representing extinction of the speckle field at inhomogeneities of the permittivity induced by the field itself in a nonlinear medium with a local response. The extinction coefficient was found as a function of the amplitude of these inhomogeneities and of the angular divergence of the speckle field. The coefficient was directly proportional to the square of the amplitude of the inhomogeneities and inversely proportional to the square of the divergence of the speckle field. The experimental results were in agreement with theoretical predictions.

An explanation is given of the distribution of the radiation of platelet lasers in the far-field zone of their angular distribution on the basis of a model of coherent waveguide scattering of the laser radiation of platelet single crystals by periodically distributed optical inhomogeneities.

A phenomenological model is proposed for the recombination process in semiconductor lasers utilizing an electron transition from the conduction band to a shallow impurity level near the valence band. It is shown that the distribution function of electrons at this level may not be of quasiequilibrium nature, so that the emission line is inhomogeneously broadened.