Table of contents

Theoretical and experimental investigations were made of the transformation of the phase-polarization characteristics of radiation on reflection from a planar waveguide. When the conditions for the excitation of the guided TE and TM modes were different, a phase shift appeared between the s and p components of the reflected radiation and this shift showed a sharp resonance in its dependence on the angle of incidence. This effect was observed experimentally for waveguides with different degrees of overlap of the angular distributions of the TE and TM modes. A resonant variation of the phase shift from zero to 2π was observed.

It is shown that the laser field influences spontaneous relaxation of quantum systems and alters the relaxation scheme. New quantum kinetic equations are obtained for the density matrix of quantum systems and it follows from these equations that an additional frequency shift appears in the dispersion function of a quantum system. This shift is over an order of magnitude larger than the familiar Bloch-Siegert shift and the absorption line profile of a quantum system is found to be an asymmetric function of the laser field frequency.

A new algorithm is derived for identification with the aid of additional information on the field polarization. The efficiency of the new algorithm is compared with the original one and it is shown that, other conditions being equal, the probability of identification with the aid of polarization is always higher and its advantage over the scalar case increases on increase in the number of resolution elements of the image.

A theoretical determination is made of the spectral characteristics of an atmospheric-pressure pulse-periodic CO₂ laser taking into account the selective absorption of the radiation in the inactive zones of the resonator. It is shown that heating of the gas in these zones can strongly influence the formation of the spectrum of the output radiation. The possibility of controlling the emission spectrum by forced convection in the inactive zones is considered.

An experimental investigation was made of the emission spectrum of a pulsed atmosphericpressure electron-beam-controlled CO₂ laser having a pump pulse duration of 30μsec. It was established that lasing mainly occurs due to the P(18) and P(20) transitions with 70-90% of the total energy being released in the P(20) transition. It was found that the width of the emission line due to a rotational transition, integrated over the duration of a radiation pulse, did not exceed 2×10⁻²cm⁻¹, while the width of one of the recorded components of the line was less than 4.7×10⁻³cm⁻¹.

Calculations are made of the laser radiation intensity in the caustic of an axicon. Calculations are used to develop methods for optimizing the focusing by matching the profiles of axicon focusing elements and the intensity distribution in the initial laser beam cross section. The results are used to determine the dimensions of continuous laser sparks obtained by axicon focusing of laser radiation in a gas.

A theoretical study is made of the influence of changes in the relaxation of a three-level system in a resonance field on the dispersion, absorption, and difference between the populations of levels activated by noncoherent pumping. This change in the relaxation is due to a tendency of a thermal reservoir to create an additional difference between the populations of quasienergy states that appear under the influence of the resonance field. It is shown that as a consequence there is a considerable change in the nature of the interaction with the radiation field in laser crystals with three-level active centers when the pump power is close to the threshold. The lasing conditions are found subject to such changes. It is shown that the threshold pump power can be reduced in this case to a value at which the difference between the populations of the active levels vanishes and lasing appears because of an inversion of the populations in a system of quasienergy levels. Under transient conditions the lasing frequency near the threshold should then depend on the pump

The parameters of a magnetically tunable Zeeman helium-neon laser are calculated. A semiclassical theory is applied to a model of the J = 1→2 transition. It is shown that the theory agrees with the experimental results.

A description is given of the construction and performance of ultrafast semiconductor electric switches controlled by optical pulses. A careful design of the transmission line connected to a switch made it possible to generate electrical pulses of picosecond duration and amplitudes of the order of several volts. It was found that at high voltages the switching efficiency was limited by intervalley scattering in semiconductors in a strong electric field, giving rise to a negative differential resistance.

The Keldysh diagram technique is used in the problem of a two-level atom interacting with an external field and a thermostat. A system of kinetic equations is obtained for an arbitrary external field. The special cases of the kinetic equations in weak and strong fields are derived by going to the appropriate limits. In the case of some specific cases new formulas are found for the absorption, resonance fluorescence, and polarization of a two-level atom in an external electromagnetic field.

An analog of the Franck–Condon principle is formulated for a heterojunction laser inhomogeneous along its resonator axis and described as consisting of two composite (homogeneous over their length) active regions.

A theoretical investigation is made of the effect of gain saturation of short (1 nsec to 2 μsec) multifrequency light pulses in an active medium, in the case of cascaded transitions for the specific case of carbon monoxide. The saturation energy is determined and the gain is optimized with respect to a number of parameters. The efficiency of carbon monoxide as a medium for amplifying light pulses of 0.01-1μsec duration is found. An investigation is made of the evolution of the shape of a multifrequency signal as it propagates in an amplifier. Analytical expressions for estimating the parameters of a saturated pulse are obtained.

A study was made of the long-term stability and reproducibility of the emission frequency of a laser with internal mirrors stabilized by the method of thermal control of the resonator length using a fixed ratio of the orthogonally polarized components of the radiation. The spectral characteristics and the thermal regime of the gas-discharge tube were investigated. A theoretical estimate was made of the long-term stability allowing for the drift of the reference point and instability of the parameters of an automatic frequency control system. Experimental values of 2×10⁻⁹ for the instability and 2×10⁻⁸ for the irreproducibility of the frequency of the investigated laser were obtained.

A theoretical analysis is made of optical multistability in electrooptic crystals in the case of various mechanisms of self-diffraction gyration. A method for realization of optical bistability in the interaction of two beams is suggested and estimates are obtained for strontium barium niobate and lithium niobate.

The results are reported of numerical experiments on nonlinear dynamics of ultrashort pulses in fiber waveguides. The quantitative criteria for a structural instability of solitons in such waveguides are derived. A study is made of the influence of the optical losses on the dynamics of formation and decay of bound soliton states in fiber waveguides. It is shown that the main contribution to the rms duration of a multisoliton pulse does not come from a narrow central peak but from the pedestal of the pulse, which gives rise to additional difficulties in the development of high-transmission-rate fiber-optic communication lines utilizing solitons.

An example of a parallel four-beam interaction in absorbing liquids was used to study the influence of a thermal self-interaction of optical beams on wavefront reversal (WFR) of radiation from a neodymium glass laser having a pulse duration of 2.5–3 msec in the free-running regime. It was found that although the thermal self-interaction substantially rearranged the angular spectrum of the interacting beams, the WFR quality was high due to self-compensation of large-scale optical inhomogeneities in the nonlinear medium. However, some shortening of the duration and deterioration in the efficiency of the WFR process were observed.

An investigation was made of the specific energy characteristics of homogeneous gasdynamic CO₂ lasers with active media utilizing a mixture of pure components (N₂-CO₂-H₂O) and the combustion products of three types of fuel (C, C + B, C₇H₈) with air.

An analysis of the permissible background energy is made allowing for the matching of the main heating pulse to the target. Expressions are obtained for the necessary level of energy contrast. It is shown that in the shell compression (implosion) regime the necessary contrast may be as high as ∼10⁶.

Investigations were made of the conversion and sorption of the impurity gases CO₂, O₂, H₂, and water vapor present in the active mixture of a carbon monoxide laser with a sealed active element, utilizing ion-heterogeneous processes. A graphite cathode was employed as the active surface and reagent for a chain of physicochemical conversions. Ion activation of heterogeneous reactions between the impurities and the graphite was shown to be a radical method for controlling the chemical composition of the active medium and for optimizing it, making it possible to improve the energy parameters of a CO laser oscillator having a sealed active element, as well as to lengthen its service life and its shelf life.

An experimental investigation was made of the dependences of the cross-talk level on the parameters of a two-channel multimode fiber waveguide. The existence of a steady-state cross-talk level was established. The dependence of this level on the normalized distance between the channels was readily approximated by an exponential law. The possibility of selection of parameters of a two-channel waveguide to achieve a given cross-talk level was established.

The example of optical heating of semiconductors and plasma is used in a study of the kinetics of the initial temperature peaks and the formation of switching waves from these peaks. It is shown that the range of the peak parameters can be divided into regions of subcritical (which disperse) and supercritical perturbations. When the peak parameters are close to the boundary curve, the time dependences of the parameters (including the perturbation width) are nonmonotonic. A comparison with the case of a nonlinear interferometer confirms the fairly general nature of the main conclusions reached for various bistable systems.

Experimental and theoretical investigations were made of the energy and threshold characteristics of stimulated Raman scattering as a result of the Q₁₂(1) transition in vibrationally excited hydrogen molecules.

An investigation is made of the influence of the quantum effects during the recording of holograms on the precision of tomographic determination of the refractive index of transparent objects. Mathematical expressions are obtained for examining the optimal value of the regularization parameter in reconstruction of the function which describes variation of the refractive index over the cross section of an object.

Estimates are obtained of the losses of modes formed in the region of monotonic variation of the refractive index in a specific case for which a fairly rigorous solution can be obtained. An analysis is made of the relationship between the concept of radiative losses of such modes and the concept of the coefficient of refraction losses used by other authors.

The results are given of numerical experiments on nonlinear kinetics of the generation of pulses as a result of stimulated Brillouin scattering (STBS) in an extended channeling medium (fiber waveguides). It is shown that the main laws governing the kinetics of STBS are determined by the relationship between the transverse relaxation time of a hypersonic wave and the propagation time of light in the medium. An investigation is made of the dependence of the period and depth of amplitude modulation of the transmitted and reflected waves on the relaxation time of a hypersonic wave and on the length of a fiber waveguide. It is shown that scattered-radiation pulses can have a peak intensity exceeding the intensity of the pump pulses even in the absence of focusing of the pump radiation or of a "seed" pulse at the Stokes frequency.

Features of the optical Fréedericksz effect, which do not appear in static fields, are identified. It is shown that in the case of oblique incidence of light relative to the detector we can expect the threshold-free effect when an ordinary wave is incident on a cell with a nematic (this effect is due to the appearance of an extraordinary component in the scattering of light by fluctuations of the director) as well as the threshold effect in the field of an extraordinary wave (this effect is due to adiabatic propagation of light).

Investigations were made of the temporal and spatial coherence of the radiation emitted by a pulsed VL-10 dye laser pumped by an electric discharge excimer laser. The dye laser radiation was characterized by a high spatial coherence and it could be used in the main hologram recording methods. Examples of holograms recorded using the dye laser are given.

A compact laser amplifier utilizing a gadolinium scandium gallium garnet crystal doped with Cr³⁺ and Nd³⁺ was constructed and investigated. Efficient operation of such an amplifier with a wavefront-reversing mirror of titanium tetrachloride was demonstrated. The diffraction-limit divergence of the beam was achieved at the exits from the laser when the repetition frequency of the light pulses was up to 10 Hz.

It was demonstrated for the first time that an optical signal with specific spatial and angular characteristics can be obtained by holographic correction of wavefronts of transient fields at the exits of long sections of multimode fiber waveguides.

Frequency doubling in various powders of molecular crystals was investigated using a tunable laser utilizing F₂⁺ centers in LiF. The dependence of the converted radiation intensity on the pump frequency was used to determine the frequency interval where nonlinear phase-matched conversion can be achieved and the noncritical (90°) phase-matching frequency.

Measurements were made of the rate constants of transfer of the excitation energy by the interaction between Er³⁺ ions excited to ⁴I_11/2,13/2 states in Y₃Al₅O₁₂ crystals. The constants were used to determine the influence of the cooperative processes on lasing of an Y₃Al₅O₁₂:Er³⁺ crystal as a result of the ⁴I_11/2–⁴I_13/2 transition.

A study was made of the design and construction of an LiF crystal laser with F₂ color centers and a long service life. The processes of phototransformation of F₂⁺and F₂⁻ color centers to the neutral state were used. Active LiF:F₂ elements with low lasing thresholds of <0.01 J/cm² were constructed. A study was made of the kinetics of the lasing of F₂ color centers in LiF. The two-stage nature of the process of photoionization of the F₂ color centers in LiF was observed under the influence of 0.53-μ pump radiation. A laser tunable in the 0.65–0.74-μ range with an LiF:F₂ crystal and a 4% efficiency was constructed; its emission line width was <2 cm⁻¹ and it was capable of emitting 10⁴–10⁵ pulses in one lasing channel during its service life.

An experimental investigation was made of the dependence of the spectrum and average radiation power of a Q-switched CO laser on the period and effective angular velocity of rotation of the switch mirror. It was found that the main reason for narrowing of the spectrum at high rotational speeds was a decrease in the Q-switching time compared with the lasing-pulse rise time.

The results are given of an investigation of the luminescence and stimulated emission spectra of powder phosphors of the Na₅La_1-x Nd_x(MoO₄)₄ composition prepared by the method of solidstate synthesis. Stimulated emission of neodymium was observed under the influence of strong pumping with laser pulses of 30-nsec duration. Such emission was indicated by monochromatization of the spectrum, strong reduction in the duration of the pulses and a simultaneous steep rise of the luminescence intensity, and transformation of the excitation spectrum. The appearance of stimulated radiation had a clear threshold.

A new method is suggested for weakening the competition between opposite waves by reflection of self-pumping waves from additional population inversion gratings induced by them in the active medium. A theoretical study is made of the characteristics of a solid-state ring laser when self-pumping waves are used in the beat regime.

A study was made of the conditions under which the TEM₀₁ and TEM₁₀ modes were generated simultaneously and they formed a beam with an annular distribution of the intensity. Complete suppression of the TEM₀₀ mode ensured that the ratio of the intensity at the peak of the annulus to the intensity on the axis reached 200 and it was limited by the scattering in the optical components of the resonator. A regime of mutual locking of the frequencies of the TEM₀₁ and TEM₁₀ modes was observed and then the annular beam exhibited complete spatial coherence.

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

The Monte Carlo method was used to calculate the spectra and yields of the products of primary and secondary thermonuclear reactions in a number of high-aspect-ratio targets used in the Del'fin facility. It is shown that in the case of a deuterium-filled target the average value of the quantity obtained by multiplying the density and size of a DD plasma at the moment of maximum energy evolution can be determined from the ratio of the yield of secondary neutrons created by the ³H(d,n)⁴He reaction to the primary neutron yield. The neutron yield of the ³He(d,p)⁴He reaction depends on the degree of deceleration of the ³He ions in the active zone and can be used for plasma temperature diagnostics. In the case of a DT-filled target it is shown that the spectra and yields of recoil nuclei created by elastic collisions with neutrons are sensitive to the state of the target shell and can be used for diagnostic purposes.

A dispersive component designed for coupling radiation out of a fiber and at the same time to separate the radiation in accordance with the wavelengths was formed on a flat polished surface of a single-mode fiber waveguide by ion-beam etching through a photoresist mask. The use of this device was demonstrated by separating the frequencies in the stimulated Raman scattering spectrum of the waveguide. The coupling-out efficiency reached 55%. A study was made of the dependence of this efficiency on the polarization of the radiation traveling in such a waveguide.

An investigation was made of multiphoton dissociation of chloroethylene dichloroborane (HClC = CHBCl₂) in a pulsed CO₂ laser radiation field. The main products of infrared dissociation of the active medium were identified. It was shown for the first time that in a pulsed CO₂ laser field the chloroethylene dichloroborane molecule dissociates to give elemental boron with up to 80% of ¹⁰B.

A study was made of deuteron emission from a vacuum arc plasma stimulated by the action of laser radiation on the surface of zirconium deuteride. A family of dependences of the deuteron yield on the laser energy E_l and on the energy deposited in the vacuum arc E was obtained in the range E_l=1—25 mJ, E=0—400 mJ. A correlation was established between the deuteron formation processes in the electrode spots of the vacuum arc and in a laser plasma due to the dependence of the arcing conditions on the laser energy. It is found that an energy an order of magnitude higher was dissipated in the formation of a single deuteron in the electrode spots of the arc compared with that dissipated in the formation of a deuteron in a laser plasma.