Table of contents

An investigation was made of an XeCl laser with ultraviolet preionization and a 4 × 4-cm active region cross section. A half-height laser output pulse duration of 500 ns was obtained by employing a laser excitation scheme based on KMK and IK-100 capacitors. The composition of the active gas mixture influenced the duration of a laser pulse.

A rigorous analytic solution is obtained of an equation describing evolution of the difference between the phases opposite waves in a ring laser characterized by a resonator frequency nonreciprocity varying linearly with time. This solution is used in combination with the Floquet method to investigate the frequency characteristic of a ring laser with a periodic resonator frequency nonreciprocity of triangular and trapezoidal forms. It is shown that in the case of sufficiently slow modulation of resonator frequency nonreciprocity this characteristic represents a system of parametric locking bands located near a quasistatic frequency characteristic. It is shown that in the case of trapezoidal modulation of the resonator frequency nonreciprocity and a specific (optimal) ratio of the durations of constant and linearly varying components of the nonreciprocity the quasistatic frequency characteristic coincides with the ideal characteristic at low angular velocities.

New laser emission lines were obtained and identified when thulium vapor was excited by a pulsed gas discharge. The spectrally integrated specific laser output energy in the visible and near infrared regions was 20 μJ/cm³. An investigation was made of the behavior of infrared laser radiation pulses under different conditions, leading to the proposal that the transfer of excitation from closely spaced resonant levels of the thulium atom in the presence of atom–atom collisions is the mechanism for pumping the upper active levels.

An analysis was made of the conditions required to achieve high-intensity recombination pumping of levels of multiply charged ions in a longitudinal pulsed gas discharge. It was found that elastic collisions with light buffer gas atoms and ions combined with ambipolar diffusion result in fairly rapid (within 0. 1–1.0 μs) cooling of the electrons in the discharge afterglow at low (up to 1 Torr) buffer gas pressures and for small ( ~ 0.3 cm) tube diameters. Lasing was obtained for the first time by recombination pumping utilizing the λ = 375.5, 376.0, and 559.2 nm O III transitions and the λ = 335.0, 430.6, 495.4, 500.8, 515.9, 526.0, 535.3, 539.5, and 595.6 nm Xe IV transitions. This was achieved in a mixture of ~ 10 ^− 2 Torr O₂ or Xe with He, H₂, or Ne (0.1–0.3 Torr) in a tube 3-mm in diameter and 50-cm long.

An analysis was made of the operation of a two-pass neodymium pulse-periodic amplifier with a mirror based on stimulated Brillouin scattering. An average output radiation power of 0.5 W was reached in the absence of depolarization when a cylindrical active element made of KNFS-type glass was used. An output energy of 0.4 J at a pulse repetition frequency up to 1 Hz and a divergence close to the diffraction limit were obtained.

An investigation was made of the feasibility of using cavity flashlamps to develop neodymium glass amplifiers with a high gain M per pass for amplification of weak signals. Active elements made of GLS22P glass of varying diameter were inserted alternately in the internal cavity of INK-22 and INK-12 flashlamps. It was found that an increase in the density of packing the optical pumping system with the cavity flashlamps (an increase in the ratio of the radii of the active elements to the radius or the reflector) did not increase the pumping efficiency. Monitoring the effective lifetime of the excited particles established that the main reason for the fall in the amplifier efficiency with increasing pump energy (the greater the active element diameter, the steeper the fall) was the influence of superradiance processes. A gain M = 10³ was achieved in an amplifier excited by an INK-22 cavity flashlamp with an active element 6 mm in diameter and 300 mm long (the excited part was 200 mm long) when the ratio of the stored excitation energy to the pump energy was ~ 0.015.

Experimental studies were made of lasing in Ne(He)–Kr–HCl mixtures pumped by an ultraviolet-preionized transverse discharge. High-power λ = 222 nm radiation was obtained with an efficiency of ~ 0.5%, in terms of the energy stored in a capacitive storage system, with laser active lengths of 20 and 60 cm. The main mechanism of formation of KrCl* molecules was ion–ion recombination and high output energies were achieved in mixtures with a neon buffer gas using high-intensity preionization and pump powers higher than 1.5 MW/cm³.

A comparison was made of different active materials such as GSGG:Cr:Nd, GSAG:Cr:Nd, YA:Nd, and YAG:Nd from the point of view of the attainable specific output energy. The best result, 150 W/cm³, was obtained for a GSGG:Cr:Nd active element 3 mm in diameter and 50 mm long.

A report is given of lasing achieved for the first time in optically pumped molecular bromine (D' ³Π_2g→A' ³π_2u, λ_L ≈ 292 nm). It was pumped by thermal vacuum ultraviolet radiation emitted by plasmadynamic discharges of magnetoplasma compressors, formed directly in the laser active medium. An output energy of ~ 1.1 J was obtained per laser pulse of ~ 5-μs duration from a Br₂:Ar ≈ 1:450 active mixture at a pressure of ~ 4 atm. A comparison was made of the experimental output parameters of optically pumped Br₂, I₂, and XeF (B–X) lasers when their geometries and excitation energies were identical.

Results are presented of an optimization of the characteristics of a flashlamp-pumped Al₂O₃:Ti³⁺ laser using luminescent light converters. Two types of converters were tested, a liquid one and a polymer one utilizing a dye (coumarin 30). The maximum laser output energy was 130 mJ with a differential efficiency of 0.4%. The tuning range of the laser radiation was 685–920 nm.

Lasing as a result of the 3-μm ⁴I_11/12–⁴I_13/2 transition in erbium was observed at room temperature in a fianite (ZrO₂–Y₂O₃:Er³⁺) crystal. The active level lifetimes were measured and pulse-periodic operation at frequencies up to 100 Hz was achieved.

Miniature monolithic solid-state YAG:Nd³⁺ ring lasers (chip lasers) with a planar or a nonplanar ring resonator and a highly efficient pumping by a quantum-well semiconductor InGaAsP/GaAs laser were constructed and investigated. The conditions for highly stable unidirectional and bidirectional single-frequency emission were established for these chip lasers. The dependences of the output radiation characteristics on the parameters of the ring resonator, on the pumping rate and geometry, on the intensity and orientation of an external magnetic field, and on temperature were determined. The results indicated a new opportunity for detection of nonreciprocal optical effects on the basis of splitting of the spectrum of the frequencies of antiphase oscillations of the intensities of the counterpropagating waves under self-modulation conditions.

An investigation of time dependences of the spectral and spatial distributions of the radiation emitted by pulsed homojunction wide-contact PbS_1–xSe_x lasers revealed excitation of autowaves (self-oscillatory waves) of the free carrier density at two similar frequencies (≲ 10⁷ Hz). These autowaves resulted in simultaneous emission of laser radiation of two types, associated with modulation of the refractive index and of the optical gain. The width of the channels was governed by the thickness of the laser diode wafer, but was independent of the resonator width. The transverse (along with p-n junction plane) intermode spacing was governed by the amplitude and spatial period (channel width) of the autowaves. A study was made of the influence of the conditions of operation ofthe laser diodes on the autowave parameters. A strong scatter of the threshold current density in a batch of 30 injection lasers with a constant resonator length, formed freshly by four-sided cleaving from a single wafer, was attributed to changes in lateral optical confinement as a result of a change in the resonator width, which was a consequence of interference between the autowaves in the resonator induced by the lateral faces of the crystal.

An experimental study was made of changes in the polarizability of nitrogen when it was vibrationally excited in a non-self-sustained electric discharge. Using this effect, interference measurements were made of the pumping inhomogeneity in an electron-beam-controlled CO₂ laser. The spatial distribution of the energy deposition in a transverse section of the discharge gap was determined.

An analysis is made of the amplification of light in a linear chain of freely expanding plasma spheres. It is shown that an optimal distribution of these spheres on a straight line ensures more effective amplification of light due to transitions in hydrogen-like ions in the case of recombination pumping of such a system than the amplification that can be expected of a freely expanding plasma filament.

Calculations are made of the influence of the photoionization–recombination mechanism of increase in the internal losses on the lasing characteristics (lasing threshold, quantum efficiency) of dye lasers utilizing transverse optical pumping of gaseous or liquid active media.

The heterodyne method was used in an experimental investigation of the frequency dynamics during operation of a TEA CO₂ laser with a ring resonator and radiation injection. The time dependence of the change in the frequency during lasing differed qualitatively from the results of other authors. The short duration of the discharge pulses and a considerable delay of lasing relative to these pulses prevented reduction in the frequency during the initial part of the pulse. Creation of a shock wave by the discharge in the anode region lowered the lasing frequency at the end of a pulse. This was attributed to a change in the mode composition of the output radiation during lasing. A theoretical analysis was made of the factors responsible for the change in the emission frequency. At the beginning of a pulse the frequency change was dominated by heating of the active medium by the discharge current pulse, whereas at the end of a pulse the dominant effect was the influence of the shock wave on the change in the mode composition. The experimental results agreed well with the theoretical calculations.

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.

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.

A one-dimensional time-dependent model of the operation of a CO₂ laser with an unstable low-magnification resonator is adopted. This model allows self-consistently for the discharge, gasdynamic, and optical processes and this makes it possible to investigate stimulated scattering in a resonator. The development of optical inhomogeneities in the lasing process gives rise to oscillations in time and increases the divergence. It is shown that the self-interaction due to modulation of the energy deposited in discharge is weak.

A method was developed for the control of transverse laser modes based on the use of an inhomogeneous interferometer adjusted using piezoelectric ceramics instead of a nontransmitting resonator mirror. Two variants of a device for controlling the ratio of the powers or duration of emission of individual transverse modes were used. Experiments on an He–Ne laser demonstrated TEM₀₁–TEM₀₀–TEM₁₀ mode switching as well as continuous control of the TEM₀₁ and TEM₁₀ modes at an intermediate position; this made possible a symmetric annular distribution of the intensity. Smooth variation of the ratio of the powers of the TEM₀₀ and TEM₀₁ modes, participating simultaneously in the lasing process, was possible. The proposed method could be used to form non-Gaussian light beams and, in particular, a flat-topped beam the profile of which was reproduced during propagation in free space and under focusing conditions.

An investigation was made of matching of the spectral characteristics of an amplifier and an absorber in passively mode-locked cw lasers by a specific choice of a suitable dye mixture. It was demonstrated experimentally that this reduced the duration and increased the energy of the pulses. It is important to note that the profile of the autocorrelation function was also improved.

An experimental study was made of intracavity compression of ultrashort pulses during continuous passive mode locking as a function of the resonator geometry, the energy of the output pulses, and the spectral characteristics of the dyes. New combinations of dyes were used for the first time and these made it possible to generate pulses with duration down to 60 fs in a simple linear resonator without recourse to pulse collisions in an absorber.

An experimental investigation was made of the time and spectral–time characteristics of intracavity radiation emitted by a copper vapor active medium in a resonator formed by plane mirrors with lenses between them. The traveling-wave regime was observed in the investigated resonator. The resonator was capable not only of time division, but also of spectral separation of single-pass and round-trip output beams: the single-pass output radiation consisted almost entirely of the green component, whereas the round-trip radiation consisted of the yellow component.

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.

A basic scheme is proposed for compression of bandwidth-limited optical pulses in the course of their nonlinear conversion in a layer of a cholesteric liquid crystal.

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.

An investigation is reported of laser radiation power absorbed in a spherical shell microtarget irradiated with six laser beams. Hydrodynamic processes in the resultant plasma, refraction of the heating radiation, inverse-bremsstrahlung and resonant absorption of the laser radiation, and deformation of the plasma density profile by the optical pressure forces are all taken into account. A study is made of the influence of the irradiation geometry and of the integral absorption coefficient. The numerical results are compared with the experimental data obtained using the six-channel PROGRESS laser facility.

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.

A study was made of the optical strength (at the wavelength of 1.06 μm) of LiF crystals before and after coloration by γ-ray bombardment. The optical breakdown thresholds were determined under different focusing conditions. It was found that the γ-ray coloration process did not result in deterioration of the optical strength of LiF crystals subjected to weakly focused radiation and it increased the breakdown threshold in the strong focusing case. Possible damage mechanisms were analyzed.

An investigation was made of the development of breakdown under the influence of CO₂ laser pulses in a decaying air breakdown plasma created by an independent source. When the laser pulses were delayed by 0.1–15 ms relative to the moment of initiation of the plasma, the intensity corresponding to the breakdown threshold was more than two orders of magnitude less than the breakdown threshold of cold air. The breakdown threshold depended nonmonotonically on the laser pulse delay. The experimental results were compared with theoretical calculations of the plasma formation threshold.

A study was made of the optical strength of polymer materials subjected to repeated laser irradiation. Low-molecular additives increased effectively the optical strength.

An experimental study demonstrated that the relative intensity of stimulated backscattering, the efficiency of conversion into stimulated backscattering, and the transmission were largely determined by the position of a focal constriction of a lens focusing a laser pulse in an active medium. Focused pumping ensured that the intensity of a phase-conjugated wave and the conversion efficiency had optima at different positions of the focal constriction. The amplitude and phase of laser radiation focused in acetone changed considerably as a result of two-photon absorption and due to the hf Kerr effect. A nonlinear medium therefore made it possible to observe phase objects and inhomogeneities of strongly reflecting surfaces illuminated by laser pulses.

The geometric-optics approximation is used in an analysis of the energy relationships governing counterpropagating spherical beams under steady-state stimulated Brillouin scattering (STBS) conditions. An experimental investigation is reported of an oscillator–amplifier phase-conjugating mirror relying on STBS in nonlinear media of CCl₄ and GLS22P glass. These results are used in derivation of relationships describing the energetics of the operation of such mirrors in a wide range of pump energy densities (up to 12 J/cm²). It is shown experimentally that the efficiency of a phase-conjugating mirror made of GLS22P glass can be increased by shifting the frequency of an acoustic resonance in an STBS amplifier.

An analysis is made of the possibility of observation of Raman scattering resonances free of the influence of the Doppler effect. Such Doppler-free resonances result from the excitation of a standing wave of Raman vibrations in a gas by two standing optical waves differing in frequency by half the Raman frequency. Complete compensation of the Doppler shifts occurs as a result of simultaneous interaction of atomic particles with two pairs of counterpropagating waves. Scattering of traveling pump waves by a standing wave of Raman vibrations in the fifth order with respect to the field gives rise to resonances in the radiation at the Stokes and anti-Stokes frequencies. Coherent scattering is observed in the presence of dispersion. A resonance in the number of particles excited to the upper level of a Raman transition appears in the eighth order in the field. The expressions obtained are applied to the specific example of neon.

A theory of the generation of optical fields in a squeezed state by parametric interaction of beams undergoing diffraction is developed. Problems related to the diffraction of a signal wave are considered and allowance for the fact that the pump wave is bounded in space. The reasons for reduction in the squeezing effect efficiency are identified and the conditions for the attainment of the maximum squeezing are found.

A system for phase conjugation of Stokes radiation by a four-wave interaction involving intracavity stimulated Raman scattering (STRS) in a Raman-active medium with a nonresonant nonlinearity. This method can be used in construction of high-power sources of highly directional Stokes radiation on the basis of round-trip STRS amplifiers coupled to a phase-conjugating element. It is shown that an STRS converter utilizing organic liquids and subjected to laser pumping of less than 100 MW/cm² intensity inside a resonator can ensure a highly efficient phase conjugation with a peak reflection coefficient in excess of unity. Depending on the ratio of the Raman and nonresonant susceptibilities of a medium, there is an optimal value of the coefficient representing the degree of conversion of laser pump radiation into STRS radiation, which ensures the maximum phase conjugation efficiency.

A theory is developed for the calculation of the gain g due to stimulated resonant hyper-Raman scattering of light by polaritons in gaseous media. It is shown that throughout the tuning range of the pump frequency (including one- and two-photon resonances) a maximum of g corresponds to a dispersion curve of polaritons plotted ignoring attenuation. Theoretical results are used to analyze characteristics of hyper-Raman scattering in sodium vapor. It is shown that under normal experimental conditions the splitting of polariton branches is considerable (amounting to tens of reciprocal centimeters on the frequency scale and several angular degrees). The value of g is estimated for two-photon resonances in the case when the pump frequency is tunable in a wide range. The optimal conditions for stimulated hyper-Raman scattering are identified.

A study is made of the behavior of quantum fluctuations of optical solitons. It is shown that fluctuations of one of the quadrature components of a soliton can be reduced. In the optimal case the suppression efficiency increases on increase in the traversed distance. A strong squeezing is quite attainable.

A theoretical investigation is reported of the influence of self-focusing of Gaussian beams on the profile of a saturated absorption resonance in laser frequency standards. An analysis is made of systems with an external nonlinearly absorbing cell and an external interferometer containing a nonlinear absorber. Analytic relationships for the profile of an asymmetric resonance and a shift of its maximum in the course of local and integral photodetection of an optical beam are derived on the assumption of weak absorption and saturation.

An algorithm is derived for the reconstruction of all possible ultrashort pulse profiles from the autocorrelation intensity function. Information on the number of possible ultrashort pulse profiles is supplemented and the conditions are found for limiting the number of these profiles as a function of the precision of their reconstruction.

An experimental investigation was made of the energy (diffraction efficiency) and time (formation, storage, readout) parameters of four-wave mixing in GaAs:Cr. An investigation of the dynamics of the leading edge of a nonlinear response pulse could become an effective method for pulsed spectroscopy of photorefractive materials.

Plane phase optical components generating complex wavefronts from a spherical wave were made and investigated experimentally. The shape of a new wavefront was compared experimentally with the surface of a parabolic mirror.

Control of the statistics of emission from a gas laser was achieved experimentally by using a photodetector–pump feedback loop. This loop reduced fluctuations of the photodiode current, used to provide the feedback signal, below the shot noise level indicating that the photodiode recorded laser radiation with the sub-Poisson photon statistics.

It is shown that the classical equations describing the Brillouin scattering process can be recast into a form which is isomorphic with the Lorenz equations for turbulence. The possibility of Lorenz-type optical chaos is predicted.