Table of contents

A laser based on the amplification of light by reflection from an inverted medium was constructed. This made it possible to use a variety of active media differing in respect of the efficiency of utilization of the pump radiation and relatively insensitive to changes in temperature. The laser was a transparent waveguide resonator surrounded by an active medium with a refractive index smaller than that of the resonator material. Exciting radiation traveling in the resonator was reflected successively from the working surfaces at angles slightly smaller than the angle of total reflection of the boundary between the resonator and the active medium. In this way a thin layer of the medium was pumped and the radiation density in the layer was higher than that in the original beam.

Experiments indicated that three-layer W-type single-mode waveguides were less sensitive than two-layer waveguides. A study was made of the spectral dependence of the additional losses due to microbending and also due to regular bending of both types of waveguide. The additional losses in the W-type waveguides depended weakly on the radiation wavelength, in contrast to the two-layer waveguides which were characterized by a strong rise in the losses on increase in the wavelength. Moreover, the three-layer W-type waveguides could be deformed to smaller radii in regular bending than the two-layer waveguides.

An analysis is made of the current status of investigations of γ radiation emitted by channeled relativistic charged particles in single crystals. It is shown that the spectral and angular distributions of radiation emitted by channeled particles differ significantly from the corresponding distributions in the case of familiar coherent bremsstrahlung in crystals and they appear as a result of radiative transitions of a particle between different levels (bands) of the transverse motion. It is shown that by increasing the energy of the incident particle, it should be possible to obtain an emitted frequency in the x-ray and γ ranges as a result of the Doppler effect. Possible methods of amplifying γ radiation in a crystal are discussed. An analysis is made of stimulated radiation and the lasing threshold value of the particle current density is given.

A theoretical analysis is made of the normal polarization modes and of the effect of field rotation outside and inside the resonator of a cw neodymium-doped garnet laser with a nonplanar ring resonator. It is found that, as a result of induced birefringence in the active element, the polarization of the radiation is generally elliptic and only tends to circular when the degree of nonplaneness of the resonator is fairly high. The radiation field is rotated both outside and inside the resonator and the angle of rotation is the sum of two angles defined by the degree of nonplaneness of the resonator and the focal length of a thermal lens in the active element. The transverse modes have a degree of axial symmetry which is a multiple of the total angle of rotation of the field in the resonator. Experimental results confirm these effects.

A report is given of theoretical and experimental investigations of the kinetics of emission from a YAG:Nd³⁺ laser with a nonplanar ring resonator. Laser equations are derived allowing for the ellipticity of the polarization of the opposite waves. A numerical solution of the kinetic equations and experimental measurements show that it is possible to establish high-frequency and low-frequency self-modulation of the laser radiation and infrequent switching of the direction of emission. Under conditions of infrequent switching, the laser radiation is unidirectional and single-frequency for several seconds even in the absence of nonreciprocal elements.

An investigation was made of the influence of processes of excitation energy transfer from rhodamine 6G (donor) to cresyl violet (acceptor) during lasing in their binary solutions under conditions of inhomogeneous broadening of the electronic spectra of both components. It was found that an increase in the lasing power of the acceptor on increase in the inhomogeneous spectral broadening was due to both radiative and nonradiative energy transfer from the donor to the acceptor.

The field amplitudes are found for oscillation modes in a resonator formed by mirrors consisting of sets of retroreflecting elements such as prism or mirror corner-cube reflectors, etc. The influence of optical inhomogeneities in the resonator and of the phase mismatch of the mirror components on the behavior of the resonator modes is discussed.

A numerical investigation is made of the role of coherent effects in the generation of short pulses in a high-pressure CO₂ laser operating in the passive mode-locking regime or in the regime of regenerative amplification of short pulses. It is shown that for a certain set of laser parameters one can expect generation of ultrashort pulses of duration of the order of the reciprocal of the half-width of the gain profile.

A pulsed optically pumped NH₃ laser is modeled numerically. Calculated dependences of the output energy and laser power on the buffer gas pressure and temperature of the active medium, obtained allowing for nonlinear effects due to interaction between the pump and laser radiation fields coupled via a common level, can be used to interpret various available experimental data. An analysis is made of the dependence of the threshold excitation power on the pump radiation frequency.

An investigation was made of the nature of the dependence of the bulk laser damage threshold of solid transparent materials on the size of the focusing-lens caustic. Experiments carried out on a large number of different samples of NaCl and KCl crystals showed that for λ = 10.6 µ and the focusing-lens caustic diameter ≳ 23 µ, the dependence on this diameter was due to the presence of microdefects. It was also established that in the case of λ = 1.06 µ radiation and small caustics (5–30 µ) the same dependence could be unrelated to microdefects. A statistical theory was developed for determining the distribution function of the defect damage thresholds from the nature of the size dependence.

Some characteristics of gas lasers utilizing cascade transitions in linear triatomic molecules are discussed. General operating conditions are determined for a pulsed cascade laser with an arbitrary method of excitation and a simple technique is described for the calculation of its maximum energy output. This approach is used to analyze some features and to give an estimate of the energy yield of three-frequency CO₂ lasers with thermal and electric pumping. Practical recommendations on the development of cascade lasers are given and specific methods of improving their efficiency are proposed. It is found that under typical conditions the average radiation power at the ∼16 µ wavelength in cascade CO₂ lasers can reach 0.5–0.6 W/cm³ in gasdynamic lasers and ∼4.5 W/cm³ in an electric-discharge laser with a supersonic gas flow rate.

An investigation was made of stimulated Raman scattering (STRS) of light in SiO₂+GeO₂ multimode fiber-optical waveguides having a complex refractive index profile. By investigating STRS using a neodymium-doped garnet laser, it was possible to distinguish three waveguide structures in the multimode waveguide (two few-mode and one multimode structure) and by selectively exciting each of these, it was possible to obtain STRS in a few-mode waveguide without exciting directly guided modes in this waveguide. Qualitative information was obtained on the refractive index profile. Saturation of the pump power and of the Stokes STRS components was observed and it was found that this was related to broadening of the STRS spectral lines. When a multimode fiber-optical waveguide was pumped by 1.064 µ radiation, nonlinear effects gave rise to high-intensity radiation with a continuous spectrum in the 0.4–1.8 µ range which was observed at the waveguide exit. This wide-band source of nanosceond pulsed radiation is potentially useful both for investigations of fiber-optical waveguides and for various spectroscopic investigations.

A study was made of the influence of a laser plasma on the potential of an insulated conducting target. It was discovered that the target potential changed stepwise on illumination with a high-power TEA CO₂ laser. A step, ΔU, in the target potential was observed and the dependences of ΔU on the initial potential, laser radiation energy density, and geometrical dimensions of the illuminated region were determined. There was an optimal pressure of the surrounding air for which ΔU had the maximum value. The dependence of ΔU on the pressure was determined, when illuminating a target in air and in nitrogen. The temporal characteristics of the variation in ΔU were correlated with the time variation of the visible and ultraviolet luminescence from the plasma. A mechanism was proposed to explain the potential step accompanying the interaction of a laser-produced plasma with a charged metallic target.

A study was made of the formation of the angular distribution of laser radiation in resonators with retroreflecting mirrors. The exchange lasing was investigated and methods of suppressing it were considered. The dynamic and static optical inhomogeneities were compensated in the active medium and in the optical channel. This reduced the divergence of the output radiation by a factor of 5–10. Intracavity beam control was achieved and complex angular distributions of specified configuration were formed. Self-guidance of the radiation on a mirror target within an angle of 30 µrad was attained.

The results are presented of theoretical and experimental investigations of room-temperature YAG:Nd lasers pumped by light-emitting diodes. The lasing characteristics of a laser operated at the 1.06 and 1.32 µ wavelengths were investigated in the cw and pulsed regimes and dependences of its parameters on the temperature, pulse repetition frequency, and other factors were studied. In the pulsed regime the laser efficiency was 0.2% and in the cw regime the radiation power reached 50 and 17 mW at the 1.06 and 1.32 µ wavelengths, respectively.

The possibility was investigated of employing catalytic regeneration of the gas mixture in a cw CO₂ laser. A regenerator was made which enabled the characteristics of an electron-beam-controlled closed-cycle CO₂ laser to be stabilized without replenishing the gas mixture. The temporal characteristics of an electrical discharge in the laser are described. A mass-spectrometric analysis was carried out of the changes in the composition of the gas mixture during laser operation. A method was developed for calculating the parameters of the regenerator.

A study of the characteristics of spontaneous and stimulated emission from a pulsed electrical discharge in an Ar–Xe mixture was used to analyze the processes populating the active atomic levels of xenon, and an estimate was made of the efficiency for the transfer of excitation from argon to xenon atoms. A conclusion was reached concerning the excitation of the active levels from the ground state by direct electron impact. An improvement in the laser energy characteristics and a change in the spectral composition of the emitted radiation on increasing the xenon pressure and adding argon were associated with a considerable change in the electron energy distribution function. The transfer of excitation from argon to xenon atoms in the electrical discharge could be neglected. The latter fact is important in the design of electron-beam-controlled and electric-discharge vacuum-ultraviolet lasers utilizing Xe₂ dimers.

The spectral characteristics of radiation-colored YAG:Nd crystals grown by the Czochralski method were investigated. Some growth defects manifested in the absorption and luminescence spectra were identified. It was found that several types of radiation color centers were formed in these crystals. A correlation between the color centers and growth defects was established.

A high-Q resonator and linear polarization of the output radiation are assumed. Calculations are made of the contributions of the real and imaginary parts of the nonlinear polarizability of an absorbing medium in the resonator to each of the parameters governing the output intensity (loss factor, saturation parameter) and detuning of the output frequency from the natural frequency of the resonator (coefficients describing effects of the mode pushing and pulling type). The results are reported of an experimental determination of the output power at the wavelength of an absorption line as a function of the intensity of the applied magnetic field and it is shown that these results agree well with the calculations.

Theoretical and experimental investigations were made of the profile of an inverse Raman scattering (IRS) line in a wide range of pump intensities. Analytic expressions were obtained for the spectral density of the intensity of Stokes and anti-Stokes waves. It was found that an IRS line forms as a result of a complex combination of the Raman and parametric processes. At some value of the pump intensity a maximum appears in the background of an IRS line and initially this maximum is of interference origin. When the IRS threshold is exceeded significantly, the maximum transforms into an anti-Stokes stimulated Raman scattering line. This anti-Stokes line does not prevent the observation of IRS as a result of the same Raman-active transition. The results are reported of an experimental investigation of the 992 cm⁻¹ line of benzene carried out using one and two cells in a collinear IRS configuration. The results obtained are found to be in qualitative agreement with the theory.

Consistent application of the averaging method in the solution of equations describing generation of opposite waves in a ring laser in the presence of backscattering shows that the frequency characteristic of such a laser has a component which is not reversed when the sign of the frequency nonreciprocity of the resonator is altered. If the coupling between the waves is weak, this nonreversible component is governed by a combination of fourth-order coupling coefficients and it disappears when the coupling is symmetric. The nonreversible component depends strongly on the parameter of a nonlinear interaction of the waves in the active medium and it can vanish for a certain value of this parameter. Phenomena associated with synchronous reversal of the amplitude and frequency nonreciprocities of the resonator are also considered.

A statistical description of four-wave parametric scattering of complex optical fields is used to investigate interaction of high-power radiation with a transparent nonlinear distorting medium and a nonideal wavefront-reversing mirror. It is found that the regime involving compensation for nonlinear perturbations of the wavefront based on averaging these perturbations is unstable when the coefficients of energy reflection from the reversing mirror are high (of the order of or greater than unity). Possible conditions for suppression of this instability are discussed.

An experimental investigation was made of natural fluctuations of the difference between the frequencies of opposite waves in an He–Ne ring laser emitting at the wavelength of 1.15 µ when the excess over the lasing threshold was up to a factor of 2.5. The dependences of the spectral density of these fluctuations on the output power were determined when this power was varied by introducing the losses into the resonator or by altering the pumping rate. The experimental results were in good agreement with a phenomenological theory. The nature of saturation of the active medium was also determined: it differed from the usually assumed approximation for an inhomogeneously broadened gain profile.

Single-mode fiber-optic waveguides were constructed. They had an SiO₂ + GeO₂ core and an SiO₂ cladding, with weak internal birefringence. These waveguides were capable of distortion-free transmission monochromatic linearly polarized laser radiation over fiber lengths of from several centimeters to several hundreds of meters. A study was made of changes in the birefringence which occurred when external mechanical forces were applied to a waveguide (bending, tension, compression, torsion). It was found that on winding a waveguide into a coil of particular radius, without applying tension, the birefringence remained weak, while if tension was applied during the winding process the birefringence increased sharply. The possibility of controlling the birefringence is of practical interest in constructing various types of optical devices.

An experimental study was made of the effects of laser radiation of 5×10⁵–5×10⁶ W/cm² power density on porous materials, including molybdenum, nickel, bronze, and YuNDK35T5 alloy. The changes in the geometric characteristics of craters formed in these materials were analyzed. Mechanical tests were made on the samples. The dependence of the volume of the removed material on the porosity was determined and analyzed. Qualitative conclusions were drawn on the mechanisms of the ejection of a material from the interaction zone.

The parameters of diffused channel waveguides in Y-cut LiNbO₃ were determined and the mode field distributions were calculated. Various operating conditions in an interference modulator were analyzed and the values of the control voltage were determined as a function of the distance between electrodes.

An experimental investigation was made of the dependences of the lasing threshold, power, and spectrum on the thickness of a crystal, reflection coefficients of the resonator mirrors, and rate of scanning with an electron beam. The reasons for catastrophic degradation of laser screens at 300 °K were analyzed. Estimates were obtained of the maximum power and optimum diameter of the electron beam for a CdS laser screen operating as a television raster at 300 °K.

A numerical study is made of the interaction of laser radiation with different isotopic forms of potassium, ³⁹K and ⁴⁰K, for time intervals shorter than the relaxation times. The quantum efficiency and selectivity of the process are determined. The behavior of the atoms is considered using the Schrodinger equations for the probability amplitudes. Account is taken of the effects associated with hyperfine splitting of the levels, their degeneracy, and the Doppler effect. Excitation by a single traveling wave and by two oppositely traveling waves is considered and the excitation characteristics of the two regimes are compared.