Table of contents

Lasing was observed in neon (λ = 585.3 nm) when dense (0.2–3 atm) Ne–H₂ and Ne–Ar mixtures were pumped by an electron beam (40 A/cm³, 80 nsec). A population inversion appeared because the lower active level was cleared by the Penning reactions involving H₂ and Ar.

Thermally induced optical damage and local "bleaching" of an optically inhomogeneous lithium niobate crystal doped with neodymium ions were observed under the influence of laser radiation.

A study is made of the possibility of a population inversion as a result of the 1s2p³P→1s² transition in He-like ions of the elements with z = 6–15. The ions accumulate in the upper state 1s2p³P as a result of optical pumping of an active medium containing Li-like ions by radiation from a laser plasma followed by a spontaneous transition to the ground state. The wavelength of the radiation due to this transition is 0.6–4.1 nm and the gain is 10⁻²cm⁻¹. A study is made of the possibility of increasing the gain by compressing the active medium.

The correlation function of a field scattered by a rotating rough surface is obtained. The statistical structure of the Doppler spectra of the field and their relationship with the image of the scattering surface is analyzed. It is shown that methods of reconstructing an image from projections can be used to obtain two-dimensional images of a scatterer from averaged Doppler spectra.

An analysis is made of the correlation structure of the Doppler spectrum of a coherent signal scattered by a rough rotating surface. A study is made of the cross-correlation characteristics of the Doppler components of spectra obtained under various conditions of broad-band probing. It is shown that these characteristics are related to the image of the scattering surface. Some estimates of the resolution are made.

An analysis is made of some features of the dynamic structure of Doppler spectra of a coherent signal scattered by a rotating surface for long intervals of spectral analysis. It is shown that the dynamic parameters of the Doppler spectra are related to the two-dimensional image of the scattering surface. Constraints on the resolution of Doppler methods of constructing two-dimensional images under real conditions are studied.

An analysis is made of superradiance in an extended two-level system. A new quantum-mechanical approach is proposed for the investigation of the evolution in space and time. A new system of integrodifferential equations is obtained and this system predicts a wider superradiance pulse and thus improves the agreement with experimental data.

An investigation is made of the stability of steady-state reflection from a boundary of a nonlinear medium with respect to the growth of small three-dimensional perturbations. It is shown that in the range of parameters of interest, where the plane monochromatic wave reflection theory predicts hysteretic effects and bistable states, the nonlinear refraction regime is instable. The dependence of the growth increment on the perturbation wavelength is determined for an arbitrary angle of incidence and an arbitrary incident wave intensity. The nonlinear stage of the development of an instability is investigated numerically in a one-dimensional approximation. In the bistable region a transition is discovered to a self-oscillatory regime in which periodic switching takes place between total internal reflection and transmission.

An analytical theory is considered of recombination pumping of H ions in a low-temperature plasma. A simple formula for the gain is obtained. The theory makes it possible to analyze the gain in the low-temperature range of most interest for applications.

Investigations were made of the energy and spectral characteristics of the stimulated emission from flashlamp-excited mixed solutions of oxazine 17 and rhodamine 6G in the following organic solvents: ethanol, acetone, isopropanol, ethylene glycol, and dimethylformamide. It was found that the energy parameters of this system are improved when both components are involved in stimulated emission. Transfer of electronic excitation energy as a result of flashlamp pumping did not appreciably alter the lasing efficiency of the two-component systems. The spectral and energy properties of these systems were strongly influenced by the triplet states of the dye molecules. Heterogeneous dye association compounds have a specific influence, depending on the solvent used.

Observations are reported of fluctuations in the polarization state of radiation from a CO₂ laser having an unstable resonator without selective elements. A connection is established between such fluctuations and changes in the spectral composition of the radiation during lasing. A demonstration is given of the influence of the effects discovered on the penetration of laser radiation into long metal channels which can be manifested in deep-penetration laser welding.

It is shown that modulation of the intensity of the radiation emitted by continuous-flow lasers with unstable resonators may give rise to optical inhomogeneities. Expressions are obtained for the natural frequencies of perturbations and for the instability increment. An analysis is made of the effects of pumping of an active medium in a resonator, of the exchange of excitations between molecules, and of the relaxation process on the rate of growth of optical inhomogeneities in CO₂ lasers.

A high-speed photographic method was developed for measuring the spatial and temporal characteristics of pulsed laser radiation in the middle infrared range. An investigation was made of the dynamics of the angular divergence of a beam from a cryogenically cooled electron-beam-controlled CO laser with different types of resonator. The main factors limiting the angular divergence of the radiation from such lasers were found to be inhomogeneity of the cooling of the active medium and gasdynamic perturbations arising from a nonuniform distribution of the pump energy.

A program for the calculation of the energy characteristics of amplifiers, based on the Monte Carlo method, was used to calculate the characteristics of a disk amplifying stage with a transverse pump system and an aperture of 15 cm. A study is made of the influence of various physical factors on the efficiency of an amplifier and, in particular, the role of the 0.35 μ absorption band of neodymium was identified. The results of the calculations are compared with the available experimental data. It is shown that when the laser pulse duration is 1 nsec, the efficiency of a multistage disk laser can reach ∼0.15% and the efficiency of the final stage can be ∼0.3%.

A theoretical investigation is made of generation of a continuous sequence of picosecond pulses in the case of resonant high-frequency pumping of an injection laser with an external resonator. Multiple transit of a light pulse through the components of a ring resonator is considered and the parameters of a steady-state pulse are determined. The active medium is regarded as consisting of two parts, one of which exhibits weak nonlinear absorption. The problem is solved by an iteration method on a computer. A study is made of the influence of the laser parameters on the duration, asymmetry, and energy of the pulses. A comparison is made with experimental results.

A new method was developed for measuring weak absorption in bulk materials and coatings. It is based on recording a change in the integrated thermal radiation flux from the surfaces of samples heated by periodic laser radiation pulses. The possibility is discussed of making absolute measurements by simulation of surface heat sources in the materials investigated, and also by comparing them with standard samples. The sensitivity of the method is estimated and the results of absorption measurements on a number of materials are presented. Consideration is given to limitations imposed on the operating range of laser pulse repetition frequencies by the thickness of the layer of the substance emitting the thermal flux and by the increase in the transverse dimensions of the illuminated area arising on account of thermal diffusion.

An experimental investigation was made of the noise of AlGaAs injection lasers in the 10–100 MHz frequency range. It was found that under steady-state conditions the fluctuation level is governed by the width of the laser emission spectrum.

Tunable laser systems with spatial intracavity separation of the emission lines are considered. The operating features of the lasers in the visible and infrared spectral regions are discussed. Resonators of the chosen type are shown to be suitable for pulsed TEA CO₂ and dye lasers. Line selection was achieved in the cw regime for an argon laser and a CO₂ laser with frequency stabilization based on the power maxima of the emission lines, leading in turn to stabilization of the output power.

An analysis is made of the formation of an optimal wavefront by flexible mirrors designed for compensation of nonlinear distortions (thermal and Kerr defocusing) of optical radiation. Calculations are made of the dependences of the compensation quality criterion and of the necessary number of drives on the ratio of the radius of action of a single drive to the initial beam radius.

An experimental investigation was carried out of the dynamics of vibrational multiphoton excitation of molecular ethanol by a CO₂ laser pulse. Energy transfer from a resonant laser-excited vibrational mode to a nonresonant mode was studied. The energy of the nonresonant mode was measured by recording the infrared fluorescence with nanosecond time resolution. In a wide energy range the intensity of the spontaneous infrared fluorescence is found experimentally to be proportional to the number of photons in the corresponding vibrational mode of a gas of polyatomic molecules. A simple expression is given for the dependence of the average energy in the mode on the total energy of the equilibrium gas. It is shown that the distribution function during the multiphoton excitation process is of a nonequilibrium nature. The lower limit of stochastization of the vibrations in the ethanol molecule is estimated.

A theoretical analysis is made of the accuracy of measurements of rotation in an inertial space using ring lasers. The main source of error is assumed to be random components of frequency pedestals. An analysis is made of the dependence of the error on the angular velocity vector as a function of time. Approximate equations are derived for the diffusion coefficients in the diffusion-like time dependence of the error variance.

An investigation was made of the spectral characteristics of planar stripe (contact width 6–8 μ) lasers made of AlGaAs heterostructures. The steady-state emission spectrum could be of multimode type because of the high level of spontaneous emission in the lasing mode. The spectrum then became narrower on increase in the power and in the limit changed to the single-mode form. However, in the presence of self-modulation processes the multimode nature of the emission spectrum could be explained by a theory of transient effects and in this case the width of the spectrum increased on increase in the power.

A theoretical study is made of the influence of the scattering on the wings of the angular distribution of radiation emitted from a laser with a plane-mirror resonator. The calculations are confirmed by a numerical experiment.

An experimental investigation was made of the contrast ratio of subnanosecond light pulses shaped by high-speed deflectors utilizing lithium niobate, KDP, and DKDP crystals. It was shown that the main factor limiting the contrast ratio is the scattering of light in the optical elements of the shaping system, for example, in the deflectors. The possibility is indicated of suppressing the influence of light scattering in real laser systems employing a pulse shaping deflector system and of obtaining a contrast ratio of ∼ 10⁸.

Highly efficient solid-state neodymium microlasers pumped by an energy of 0.2–1 J were constructed. This energy was provided by flashlamps in which the discharge gap was less than 15 mm. In the free-running regime the lasing efficiency reached 2%, whereas in the -switched regime it was 1.3% and the pulse duration was 2 nsec.

Optical probe studies were made of a laser plasma in the ablation regime of heating of thermonuclear targets. Exact synchronization of a short (0.4 nsec) probe laser pulse with a heating radiation pulse (4 nsec) was ensured by a system based on a two-transit Pockels cell. The probe and heating pulses were formed by the same electrical pulse applied to a two-pass Pockels cell in the case of the probe radiation and to a conventional Pockels cell in the case of the heating radiation. The duration of the short probe laser pulse obtained in this way was approximately equal to half the duration of the leading edge of the electrical pulse. Frame interferograms of the laser plasma were recorded.

An experimental investigation was made of the acoustic perturbations that appeared in absorbing condensed media when their surfaces were exposed to laser pulses. Changes in the profile of a photoacoustic pressure signal were recorded for the first time and these could be due to the melting of the irradiated substance.

A new method for determining the optical nonreciprocity is suggested and analyzed. The method is based on the use of a ring laser operating in the self-modulation regime with a variable-sign frequency "pedestal." The example of a ring YAG laser is used to show that this method should make it possible to reduce greatly the experimental error.

An investigation was made of fluctuations of the output frequency of a pulsed diode laser emitting at ∼ 10μ. An analysis of signals transmitted by a Fabry–Perot interferometer made it possible to determine the frequency dispersion Δν_l ≈ 2.5 MHz for a normal distribution law and also the correlation time of frequency fluctuations, which was 0.2 μsec.

An experimental investigation was made of the transformation of the intensity profile of a spatially confined light beam transmitted by optical bistable devices based on thin-film semiconductor interferometers formed by vacuum evaporation. A hysteresis of the intensity profile and switching waves was observed: these waves represented the process of consecutive transition from one stable state to another in neighboring zones of the interferometer. An experimental investigation was made of the velocity of switching waves in thin-film interferometers and in a model interferometer with a thermal nonlinearity.

Aberration distortions were determined at the focus of a spherical geodesic lens made from a waveguide formed by the diffusion of Ti in a Y-cut LiNbO₃ crystal. The experimental results were compared with calculations carried out in the geometric-optics and diffraction approximations. For a lens with a focal length f = 8.6 mm and a relative aperture of the incident beam amounting to 0.67, the size of the spot at the focus was ∼ 4 μ when the relative amplitude of the side lobes was 9dB.

A numerical solution is obtained of the problem of generation of an electric current and of a magnetic field in a plasma formed by interaction between laser radiation and the surface of a conducting target. The contact potential and the thermo-emf of an inhomogeneous plasma are considered as emf sources. The distribution of hydrodynamic parameters in a jet is deduced from a numerical solution of an axisymmetric problem. The distributions of the current and of the associated magnetic field are determined.

A method for making direct measurements of the difference between the anharmonicities of the hydrogen molecule is proposed and implemented. It gives [ν{₀₁(1)} — ν{₁₂(1)} — ν{₁₂(1)} — ν{₂₃(1)}] = 4.837 ± 0.001 cm⁻¹ if the reference lines are components of the complex spectrum of four-photon parametric light scattering accompanying stimulated Raman scattering due to the ₀₁(1), ₁₂(1), and ₂₃(1) transitions. The measured anharmonicity difference can be used to calculate the frequency of the ₀₃(1) transition in the hydrogen molecule reduced to zero gas density: ν{₀₃(1)} = 11765.003 ± 0.001 cm⁻¹ .

An investigation was made of the characteristics of the radiation emitted by injection lasers with an external mirror and different levels of the optical coupling. Variation of the optical length of a laser or of the external resonator modulated the emission wavelength and radiation power and such modulation differed in the case of weak and strong coupling with the external mirror. In general, power modulation had two components (fast and slow) and a tilt of the external mirror gave rise to an additional component.

Planar focusers ensuring formation of an axially asymmetric distribution of the intensity of CO₂ laser radiation, of the type used in ophthalmic surgery, are described and considered. Special attention is given to laser treatment of myopia (laser keratotomy). The promising nature of the proposed method is demonstrated.

A narrow-band picosecond parametric oscillator was constructed. Radiation from a GaAs semiconductor laser was injected into this oscillator and it was pumped by 40 psec pulses of the second harmonic of a garnet laser. The output was in the form of picosecond pulses which were frequency-tunable near the signal λ _s = O.85 μ and idler λ _i = 1.4 μ wavelengths. The pulses were nearly bandwidth-limited with Δν = 0.6 cm⁻¹ and with an energy of 50 μJ.

A laser flashlamp pumping system having an input energy of 330 J and a pulse duration of ∼ 230 nsec was developed experimentally and tests were made using a solution of rhodamine 6G under lasing conditions. The maximum lasing energy was 1.1 J, the efficiency was 0.33%, the angle of divergence of the beam at half-energy in a planar resonator was 1.2–1.3 mrad, and the illumination of an ethanol solution of rhodamine 6G halved the output energy when the intensity was 170 kJ/liter.

A hypothesis of "frozen" turbulence in separate horizontal layers of the atmosphere and an allowance for the external turbulence scale are used to find the matrix of the moments of the coefficients of the expansion of a wavefront on an aperture in terms of the Zernike polynomials. It is shown that the aperture has an averaging effect on lower-order aberrations and that it causes a deterioration in the precision of representation of the wavefront by a finite number of such polynomials with coefficients averaged over the measurement time. An example is given of a calculation of the characteristic time of the "frozen" phase distribution over the aperture.

Calculations are made of the compression ratio of the plasma of the simplest type of a shell target exposed to a laser pulse whose power increases with time in accordance with a power law and whose duration is shorter than the shell implosion time. It is found that as the exponent in the law describing the increase in the laser pulse power rises the entropy coupled into the compressed target material by the shock wave during motion of the shell decreases and consequently the final plasma density increases.

An experimental investigation was made of the effective coefficient representing the absorption of energy from a high-power cw laser beam by metals. The efficiency of energy transfer from the beam to a target in He was found to be considerably higher than in Ar. A qualitative explanation of the observed dependences was provided.

The results are presented of theoretical and experimental investigations of the gain and emission spectrum of a TE laser utilizing a mixture of isotopically substituted ¹²CO₂ and ¹³CO₂ molecules. It was found that, in a wide range of active-medium pressures (p = 100–3500 Torr) and excitation levels (T₃ = 1200–2400 K), a gas mixture such the concentration of ¹³CO₂ (x₁₃) and ¹²CO₂ (x₁₂) molecules satisfied the condition x₁₃/(x₁₃ + x₁₂) 0.35–0.45 emitted one or several lines in the wavelength range between 11.11 and 11.22μ [between P(16) and P(26) in the 00⁰1-10⁰0 band of the ¹³CO₂ molecule] in a laser with a nonselective resonator. The lasing efficiency was approximately equal to that for ¹²CO₂. The results of calculations were in good agreement with the experimental data.

An experimental study was made of modulation of argon laser radiation (λ = 488 nm) by broadening of the n = 1 level of the A exciton in CdS pumped by an electron beam. A relative change of about 100% in the transmission and an absolute change of about 0.4 were observed.

A study was made of the kinetics of emission from a neodymium laser subjected to selective pulsed pumping. The influence of the excitation energy relaxation processes on the shape of the stimulated emission pulses was determined for pumping of neodymium glasses in short-base resonators by radiation pulses of 2 nsec duration and 0.53 μ wavelength. A numerical model was developed for the description of the lasing kinetics of neodymium glasses subjected to selective pulsed pumping. The time constants of the relaxation of the excitation energy from the ⁴G_7/2 level to the metastable ⁴F_3/2 level of Nd³⁺ ions were estimated for silicate (GLS-14) and phosphate (KNFS) glasses.

An investigation was made of the evolution of the time profile of a high-power CO₂ laser pulse during its transmission by absorbing molecular gases C₂F₆ and SF₆. The effects observed were associated with an anharmonic shift of the infrared absorption band of the molecule when it became vibrationally excited.

A calculation is made of the steady-state threshold of stimulated scattering in the forward and backward directions in a medium characterized by linear amplification. A numerical investigation is made of the steady-state stimulated scattering in the forward and backward directions under saturation conditions and a comparison of the two sets of results is made.

The first investigation was made of the optical strength of gadolinium scandium gallium garnet (GSGG) crystals doped with both Cr³⁺ and Nd³⁺ simultaneously. The high optical strength of these crystals was not affected by irradiation with γ rays. An investigation of the damage statistics led to the conclusion that the microdefects played the dominant role in the optical strength of GSGG:Cr³⁺:Nd³⁺ crystals.

Lasing was observed at 14 wavelengths in the yellow-red part of the spectrum as a result of electronic transitions in the Te₂ molecule in tellurium vapor pumped optically by He–Sr recombination laser radiation (λ = 430.5 nm). The strongest lasing lines corresponded to the BO_u⁺ (ν' = 1–4) →XO_g⁺ (ν'' = 36–38) transition in the ¹²⁸Te₂ or ¹³⁰Te ¹²⁶Te molecules.

Effective population of the first overtone 2ν₃ of the SF₆ molecule was achieved by the application of two laser fields detuned symmetrically from resonance. This method revealed a structure of the multiphoton excitation spectrum of the OsO₄ molecule in the range of frequencies inaccessible to monochromatic CO₂ laser radiation.

Short and ultrashort infrared radiation pulses were produced by double consecutive generation of the difference frequency between two lasers, when one of them (for example, a CO₂ laser) determined the spectrum and emission line and the other provided the necessary pulse duration. This method was used to generate pulses of 20 nsec duration and 10 kW/cm² intensity in the CO₂ laser emission range.

The spread function is found for degenerate four-photon conversion with rotation. Estimates are given of dependences of the resolution of the radiation converter on the rotation, on the detuning of the image plane from the object plane, and on the divergence of the pump wave.

A theoretical study is made of the possibility of maximization of the sharpness function in a specific adaptive system. It is shown that the known maximization methods produce local maxima which do not satisfy the requirement of a system for compensation of phase distortions.

A shift of the Si⁺¹³ + e⁻→Si⁺¹² + hν recombination discontinuity was recorded in the emission spectra of glass shell targets: this shift was Δε = 100 ± 20 eV corresponding to a plasma density 1–3 g/cm³. The experimental results were compared with numerical gasdynamic calculations

A description is given of a laser with switching in a resonator by a passive laser switch. It is shown that control of the moment of emission of a giant pulse in a compound (three-mirror) resonator can be provided by an electrooptic switch. In this case the requirements in respect of the parameters of the switch can be relaxed considerably.