Table of contents

Constants of the Sellmeier equations were determined for a KTP crystal in the 0.4–4.0 μm wavelength range. Calculations were made of the angular tuning characteristics for various types of interaction in the principal crystal planes. Some of the tuning characteristics were checked experimentally.

A systematic investigation was made of photorefractive and nonlinear optical properties of LiNbO₃:Mg, LiNbO₃:Fe, LiNbO₃:Mg:Fe and LiNbO₃:Mg:Nd crystals grown from congruent melts with a wide range of dopant concentrations. The nonlinear optical properties depended nonmonotonically on the impurity concentration and strong suppression of photorefraction was observed when the magnesium concentration was more than 1%. Crystals containing 2.6% Mg were used for second harmonic generation of radiation emitted by a YAG:Nd³⁺ laser at room temperature with a conversion efficiency of 25%.

An experimental investigation was made of the gain in cataphoretic cadmium vapor lasers at 0.44 μm. It was found that when the striations were synchronized, the gain increased by approximately 15% due to an increase in the excitation of the active levels by fast electrons. Scaling laws typical of an He–Cd laser were determined for conventional excitation of the active medium, excitation with synchronized striations, and application of a longitudinal magnetic field.

Investigations were made of a pulse-periodic electric-discharge XeCl laser with two types of resonator. When an unstable confocal resonator with a magnification of M = 12 was used, the divergence exceeded the diffraction limit by a factor of only 2–3 and there was only a slight ( ≲ 30%) reduction in the output energy relative to that from a laser with a plane–plane resonator. The influence of the pulse repetition frequency on the radiation divergence was investigated for helium- and neon-containing gas mixtures. A dependence of the divergence on the pulse repetition frequency was discovered. A theoretical interpretation is given of the results of the experiments.

The problem of spreading of the current is solved exactly using a model with a stripe contact. The efficiency of pumping of a laser with an alternating current is determined.

An investigation was made of variation of the pulse repetition frequency in a passively mode-locked injection laser. The generation of ultrashort laser pulses was observed at four harmonics of an external resonator when its length was constant. Dynamic variation of the pulse repetition frequency was readily achieved by changing the laser pump current. Analytical dependences were in good agreement with the experimental results.

It was shown theoretically that the use of a nonlinearly absorbing cell inside the resonator of a laser leads to a reduction in the width of the laser emission line by a factor of S in the case when apparatus-induced fluctuations are dominant, and by a factor of S² for the case of natural fluctuations (S is the autostabilization factor). It was established experimentally that S reaches a value of ~ 25 in an injection laser with a nonlinearly absorbing cell containing cesium vapor, and that this enables one to improve substantially the monochromaticity of the radiation from injection lasers without increasing their dimensions.

An investigation was made of the influence of phase modulation of picosecond pulses on their amplification in a CO₂ amplifier. Linear frequency modulation of the input pulses was not maintained during amplification. This casts doubt on the possibility of compressing such amplified pulses. However, amplification of chirped picosecond pulses in a CO₂ amplifier makes it possible to generate a train of ultrashort pulses with a high ( ~ 10¹² Hz) and controlled repetition frequency.

A model is proposed for the dynamics of evolution of various transverse modes in the resonator of a passively Q-switched laser. On the basis of this reasoning, a double-pulse YAG:Nd³⁺ laser with a delay between pulses controllable in the 20–100 ns range was implemented experimentally. A satisfactory agreement was obtained between the parameters of the real laser and the results of the numerical calculations. By using this laser to irradiate a target, it was possible to improve severalfold the contrast of the laser plasma luminescence spectrum.

A simple and convenient method of synchronous pumping of jet organic dye lasers is described. In this method a cw argon laser with sinusoidally modulated radiation is used as the pump source. The argon laser is modulated by a standing-wave acoustooptic modulator operating at the frequency of intermode beats of the dye laser. The results are given of an experimental investigation of the width of the mode locking range under synchronous pumping conditions and of the time and energy characteristics of the output radiation. The duration of the output pulses of the dye laser was ~ 350 ps under synchronous pumping conditions.

Lasing was observed in iodine atoms perturbed by xenon at pressures up to 30 atm. A reduction in the delay of the laser pulse relative to the beginning of the pump pulse with increasing xenon pressure confirmed that there is a broad strong IXe(1/2)'→(1/2)'' exciplex transition and opened up the possibility of generating picosecond laser pulses at ~ 1.3 μm.

An efficient regenerative YAG:Nd³⁺ amplifier with a stimulated Brillouin scattering (STBS) mirror operating on a weak initial signal was developed. An investigation was made of the compression of the initial pulse under the combined influence of STBS and nonlinear amplification in the active medium.

A study was made of the structure of radiation from a cw CO chemical laser when the rate of flow of the reagents through the optical resonator was subsonic. It was found that the laser delivered unpolarized radiation with a divergence of 6–8 mrad, but this divergence decreased as the pressure of the medium increased.

A pulse-periodic laser has been developed utilizing a new active medium, a gadolinium scandium aluminum garnet crystal activated with chromium and neodymium. An absolute free-running efficiency of 3.4% with a differential efficiency of 4.4% was obtained in the single-pulse regime. Thermooptic effects in the new active medium were approximately 1.5 times weaker than those in scandium gallium garnet crystals. The damage threshold for cylindrical active elements with a mat surface was approximately 500 W per centimeter of the active element.

The maximum attainable average output power of an Sr–He recombination laser (λ = 430.5 nm) was ~ 14 W/m limited by overheating of the active medium. An average output power of 3.9 W at a pulse repetition frequency of 29 kHz was obtained using a water-cooled laser tube 33-cm long and 1 cm in diameter.

Laser radiation was generated in zinc sulfide crystals by streamer excitation using both transverse and longitudinal systems for coupling out the radiation. The output power was 170 W (T = 77 K) in the first case and 1 kW (300 K) in the second. A study was made of the crystallographic orientation of the streamer tracks in zinc sulfide single crystals containing between 2% and 10% of the hexagonal phase.

It is shown numerically and experimentally that injection of a high-power train of nanosecond pulses (instead of one pulse) into a controlled CO₂ laser with an active volume of 50 liters makes it possible to widen considerably the range of regenerative amplification and to control the time structure of the radiation within wide limits.

Simultaneous stimulated emission at two controlled wavelengths has been reported in a tunable laser utilizing color centers in an LiF crystal excited by garnet laser radiation with a high pulse repetition frequency. The results of experimental studies of the spectral and temporal characteristics of the radiation are reported.

A theoretical investigation was made of the lasing characteristics of CO₂ lasers with active media containing molecules of ¹²C¹⁶O₂, ¹³C¹⁶O₂, ¹²C¹⁸O₂, and ¹²C¹⁶O¹⁸O. The dependences of the lasing efficiency on the input energy, the Q factor of the resonator, and the degree of enrichment of carbon dioxide with a particular isotope were determined. The calculations were carried out allowing for the partial overlap of the lines due to different vibrational–rotational transitions and use was made of new data on the probabilities of spontaneous emission from the investigated molecule. The results were in good agreement with the published experimental data.

A study was made of the contribution of electronic excitation energy transfer processes and the gain factor to the stimulated emission from various ethanol solutions of rhodamine and oxazine dyes due to flashlamp excitation. A method is proposed for calculation of the power density of the radiation absorbed by the acceptor molecules taking into account energy transfer from the donor to the acceptor and overlap of their gain spectra. Estimates are also made of the direct contribution of the excited donor molecules to the stimulated emission flux in the acceptor band. The calculated values are compared with the relative change in the output power of the mixture due to the introduction of a donor component into the active solution.

The observation of luminescence from iodine atoms (λ = 1.315 μm) was reported when methyl iodide (CH₃I) and propyl iodide (C₃H₇I) were added to a stream of products from a chemical singlet oxygen generator containing chlorine. The effective rate constant of the atomic iodine formation process + products was determined: k₁₀ ≈ 4 × 10^{− 32} cm⁶/s for R = CH₃, C₃H₇. In the case of fluorine-substituted alkyl iodides (R = CF₃, C₃F₇), no luminescence was observed from excited iodine atoms. The presence of chlorine in the active medium of a pulsed oxygen–iodine chemical laser reduces substantially the lifetime of the stored energy. Appropriate estimates are given.

An analysis is made of the possibility of constructing a cw laser converting solar radiation in a gaseous active medium consisting of a mixture of homonuclear and heteronuclear dimer molecules (which may be metal vapors) and a rare gas as a buffer. A population inversion is established in such a system as a result of photodissociation of dimer molecules into atoms in excited and ground states followed by recombination of the lasing atoms back to the original molecule as a result of three-particle collisions with the buffer gas atoms. It is shown that this system has a number of important advantages such as the chemical stability of the active medium during optical pumping, resistance to pyrolysis, and also a fairly high efficiency of ~ 3% at a relatively low degree of concentration of the solar energy ξ ≈ 50–100.

An emission band corresponding to the B →X transition in the HgF molecule was recorded in the spectra of a plasma produced by a high-voltage pulse-periodic discharge in mercury difluoride and trifluoromethylmercury fluoride vapor. This indicated that it is advisable to use pumping methods based on a dissociative excitation mechanism in attempts to develop an HgF laser.

An experimental investigation was made of nonradiative relaxation of the excitation from the ⁴S_3/2 level of the Er³⁺ ion in Y₃Al₅O₁₂. It was found that quenching of the excitation from the ⁴S_3/2 level cannot be described using a single microparameter at all stages of the excitation decay process.

A single excitation source (in the form of a xenon flashlamp) was combined with spectral converters to demonstrate lasing due to F₂, F₂⁺, and F₂⁻ color centers in LiF. A universal spectrum analyzer for the investigation of gases and plasmas was constructed. Polychromatic quasi-cw lasing was excited by flashlamp pumping of color centers and this made it possible to widen the spectral range of the analyzer and to increase its sensitivity. The results indicated that it should be possible to construct "soft" apertures and switches (shutters) for visible laser radiation.

An experimental investigation was made of the emission characteristics of a coherently operating array of waveguide CO₂ lasers. The lasers were phase locked by self-reproduction of periodic light fields. Three supermodes of the array were found to exist, an investigation was made of the radiation power distribution over the aperture as a function of the active medium pumping level, and the efficiency in the coherent lasing regime was determined.

An experimental investigation was made of the spectra of natural amplitude fluctuations of counterpropagating (opposite) waves in a ring He–Ne laser under phase resonance conditions. The form of the spectrum was then qualitatively different from the spectrum obtained in the standing-wave regime. A theoretical analysis provided a satisfactory explanation of the characteristics of the observed spectra.

A study is made of the laws governing interference effects in a system of dispersive resonators coupled by diffraction. An approximate analytic expression is obtained for the selectivity function. An analysis is made of the influence of the parameters of the system on the selectivity curve. It is shown that the strongest manifestation of interference effects is observed when the difference between the Q factors of cophasal and antiphasal types of resonator excitation is maximal.

An experimental investigation was made of the processes occurring on transition from active mode locking to chaotic free running of an He–Ne laser (1.15 μm). The appearance of quasiperiodic fluctuations and chaos was due to the formation of supermodes observed experimentally. A reduction of the depth of modulation induced higher supermodes. An asymmetry of the bifurcation diagram was observed as a result of a change in the sign of the mismatch between the modulation and beat frequencies. The nature of the processes occurring as a result of suppression of mode locking was fairly complex, but the following bifurcations could be identified: period doubling, tangential bifurcation, appearance of tori. A mapping relationship was obtained to describe changes in the pulse profile from one pass to the next during propagation in the laser resonator.

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.

A fast-acting system for stabilization of the axis of the angular distribution of radiation from a continuous-flow CO₂ laser is considered. The results of a simulation experiment are reported: they show that it is possible to suppress, by 24–28 dB, fluctuations of the position of the axis in the spectral range 0–20 Hz. This makes the proposed system a promising method for large-aperture laser beams.

A comparative analysis was made of the various methods for heating a laser plasma with Nd laser radiation. Methods of heating with the first and second harmonic pulses of different durations were compared. Diagnostics by x-ray spectroscopy yielded the parameters of a recombining plasma (temperature and density) and the populations of excited levels of the Al XII ion at different distances from the surface of an aluminum target. The experimental results on population inversion of the excited levels were compared with theoretical calculations.

An experimental investigation was made of the characteristic features of optical breakdown on the surface of silicon and germanium subjected to laser pulses of wavelengths 1.06 and 10.6 μm with a short time delay between them. A theoretical analysis was made of the main experimental dependences. Reduction in the breakdown threshold at the wavelength of 10.6 μm was attributed to intraband absorption by free carriers, which appeared as a result of photoexcitation of a semiconductor with pulsed 1.06 μm radiation. A strong increase in the breakdown threshold occurred near a plasma resonance for the CO₂ laser radiation.

An analysis is made of a two-color adaptive optical system with a feedback loop closed optically via the atmosphere and utilizing an additional reference source emitting at a wavelength different from the wavelength of the main source. Calculations are reported of the variance and of the structure function of the difference between eikonals of two spherical (or plane) waves with different optical frequencies under different turbulence conditions.

A physical model of generation of spontaneous magnetic fields and of electric currents in an inhomogeneous laser plasma is developed for a wide range of laser radiation flux densities. It is shown that spontaneous magnetic fields generated in a plasma may be governed not only by the bulk emf sources, but can be influenced significantly by the processes at interfaces in a plasma (for example, at DT fuel–shell, plasma–metal, and other interfaces). A quasistationary approximation is used to formulate the boundary conditions governing the surface sources of spontaneous magnetic fields. A detailed analysis is made of an inhomogeneity of the potential of a double layer and of an effective contact emf in their role as surface mechanisms of generation of spontaneous magnetic fields. Generation of fields and currents is considered analytically in the region of an inhomogeneous interface between two plasmas and in an inhomogeneous laser jet formed as a result of interaction of laser radiation with a conducting target.

High-frequency electric currents were generated by irradiation of a metal target with CO₂ laser pulses. It was found that the region where the ambient gas was photoionized had a decisive influence on the hf current amplitude. A method for increasing the amplitude of the current by creating an auxiliary laser jet on the target was proposed and used. An hf current of up to 1 A amplitude was observed at a frequency of 75 MHz and this current lasted for 1.5 μs.

A description is given of a spectrometer capable of recording panoramic Raman-induced Kerr effect (RIKE) spectra in the range of frequency offsets from – 600 to 1600 cm^− 1. The RIKE spectra of low-frequency intermolecular vibrations of liquid water (with lines at frequencies 16, 71, and 82 cm^− 1) are reported for the first time and the results are given of a determination of the spectroscopic parameters of the corresponding continuous Raman lines.

Optical damage to YAG:Nd crystals was observed. The change in the refractive index exhibited dispersion in the visible range of wavelengths. The damage effect was due to either charge transfer or photoexcitation involving defect centers.

A numerical investigation is reported of resonant absorption by a plasma density profile with a step. It is shown that the resonance curve is affected not only by the inhomogeneity length at the point with the critical density, but also by the density at the upper and lower boundaries of the step. An analytic solution is obtained for the resonant absorption coefficient on the assumption that a plasma region occupied by the step is thin.

A numerical investigation is reported of a five-dimensional dynamic system describing a laser (specifically a CO₂ laser) with a nonlinear absorber (in the form of a CO₂ cell). Two regions of periodic modulation of the Q factor are found at low and high pressures of the absorbing gas. The laws describing the behavior of the characteristics of a sequence of pulses are based on the general theory of bifurcations and of propagation of short light pulses in amplifying and absorbing media. A mechanism in which an external noise causes stochastization of spontaneous fluctuations is identified and the conditions under which this can occur are investigated.

The results are given of theoretical and experimental investigations of the generation of vacuum ultraviolet radiation by parametric frequency mixing of radiation from a neodymium laser using higher nonlinearities of a mercury vapor. The effects of interference of nonlinear polarizations of the seventh nonresonant and ninth resonant orders are reported. Investigations of the frequency dependence of the breakdown threshold (which is the main limiting factor) make it possible to relate the reduction in the threshold to a change from ten- to nine-photon ionization.

An experimental investigation was made of a laser oscillator with a stimulated Brillouin scattering mirror located outside the main resonator. Active elements made of YAlO₃:Nd³⁺ and GSGG:CR³⁺:Nd³⁺ crystals were used under Q-switching conditions to generate efficiently radiation with a divergence close to the diffraction limit.

A new absorption spectroscopy method is proposed. This method is based on intracavity generation of sum and difference frequencies and it is analogous, in respect of its physics and capabilities, to intracavity laser spectroscopy. An investigation is reported of the dependence of the sensitivity of the new method on the efficiency of nonlinear frequency conversion and on the phase relationships obeyed by waves interacting in a nonlinear crystal. It is reported that the sensitivity of the new method in determination of weak absorption is between two and three orders of magnitude higher than the extracavity variant.

An experimental investigation was made of the influence of laser radiation pulses on the spectral and time dependences of the transmission of CdSe single crystals at T = 4.2 K. The intensity of laser pulses transmitted by such a crystal was limited in the spectral region of the ground excited state because of two-photon absorption in which an exciton state acted as an intermediate level. A giant value of the two-photon absorption coefficient, amounting to ~ 10³ cm/MW, was obtained. The evolution of photoexcited nonequilibrium electron–hole pairs was investigated.

An analysis is made of spontaneous oscillations in a laser fiber-optic heterodyne interferometer utilizing single-mode fiber waveguides forming a closed ring. A theory is given of steady-state single-frequency lasing in such a system, which represents a characteristic spontaneous oscillator with a delayed optical feedback. The condition for self-excitation and steady-state lasing are found and the frequency and amplitude of steady-state spontaneous oscillations are deduced. It is shown that a high stability of the lasing frequency is possible in a self-oscillatory system with heterodyning of optical oscillations in a reference laser. It is suggested that such a lasing interferometer can be used as a highly sensitive interferometric sensor of external perturbations of a fiber waveguide distinguished by a higher precision of manifestation of such perturbations in the frequency of spontaneous oscillations, i.e., in the quantity which at present can be measured more accurately than any other physical parameter.

An expression is obtained for the Wigner function of a paraxial light beam in terms of its intensity distribution in a bulk (three-dimensional) medium. The derivation is given for monochromatic beams with a one-dimensional transverse structure and it is based on application of the Radon transformation.

A submillimeter synthesizer was built on the basis of a backward-wave tube. A study was made of the characteristics of an optically pumped CH₂F₂ laser with an output power of ~ 120 mW at λ = 184.3 μm and 40–60 mW at λ = 214.6 μm. The synthesizer was used in determination of the frequencies at λ = 184.3 and 214.6 μm: ν₁₈₄ = 1 626 602.95 ± 1.5 MHz and ν₂₁₄ = 1 397 120.216 ± 1.5 MHz.

An experimental investigation was made of the statistical criteria of focusing of radiation on a rough reflector. The effectiveness of such criteria in compensation of static, dynamic, and nonlinear phase distortions was demonstrated. The criteria were used in experiments on a 15-channel adaptive system with a flexible mirror. This system was controlled by a computer.