Table of contents

A study was made of the modulation of the coherent emission spectrum by spatial gratings of the refractive index, produced by the dye laser field in an absorbing medium inside the resonator. It was found that the frequencies of the reflection maxima of a nonlinear mirror resulting from the inhomogeneity of the refractive index along the direction of propagation of the light wave were in agreement with the frequencies satisfying the conditions for the maxima of interference reflection in the presence of an additional plane in the resonator.

An experimental investigation was made of the influence of the resonator mirror misalignment and of the thermal deformation of the active element on the angular divergence of the radiation emitted from a laser resonator formed from frustrated-total-internal-reflection prisms acting as plane mirrors with a transversely varying transmission. It was found that such a resonator was less sensitive to the misalignment of the resonator mirrors and to the thermal deformation of the active element.

A proposal is made fot an improved method for the interpretation of interferograms which can accelerate considerably the process of measurement and increase the precision of determination of deformations of an object. The improved method is applied to thermal deformations in a soldered cylindrical glass–Kovar–copper joint.

The results are given of an experimental investigation of the change in the phase of laser radiation due to transmission through a ruby crystal. The experimental results are compared with theoretical calculations.

The generation conditions were investigated and the output characteristics were determined for the blue–green laser radiation emitted by xenon ions and for the ultraviolet radiation emitted by oxygen ions. These ions were excited in an electrodeless high-frequency discharge using excitation pulses of ~1.5 msec duration. The total pulse output power of the xenon ions was ~120 W under quasicontinuous conditions and the corresponding output power of the O II (λ = 374.95 nm) and O III (λ = 375.98 and 375.48 nm) oxygen lines was 5 W. It was found that these lines could be emitted continuously.

Estimates are given of the maximum average output powers which can be obtained from pulsed metal vapor lasers. It is shown that the average output power of sealed lasers of this type can be of the order of several tens of watts per centimeter of the discharge tube length, i.e., it can exceed by more than one order of magnitude the corresponding power obtained from the CO₂ laser.

A description is given of an iodine photolysis laser with an output energy of 50 J in the form of pulses of 5 nsec duration.

A description is given of a method for the fabrication of GaAs semiconductor lasers with an emission region several microns wide. The results are given of an investigation of the radiative characteristics of such lasers. It is reported that the emission is of the single-mode type when the threshold is exceeded by a factor of 3–4.

A method was developed for varying continuously the duration, carrier frequency, and width of the emission spectrum of a mode-locked laser. The method was based on the use of a polarization filter. A reduction of the width of the spectrum to 3 Å did not increase the minimum (10^–11 sec) pulse duration but simply increased the stability of the laser operation. Further narrowing of the spectrum to 0.5 Å increased the pulse duration to 50 psec.

A calculation is reported of the influence of the stimulated emission of a system of hydrogen atoms on the response of a hydrogen maser to a short resonance-frequency pulse. It is shown that this emission produces two effects which result in a deviation of the form of the signal from the ideal curve exp(–t/T₂). The first increases effectively the decay time of the signal and it disappears even for I/I_th ≈ 0.3, when the atomic beam is interrupted during the observation time (I is the atomic flux and I_th is the threshold value of this flux). The second effect appears when the excitation pulse deviates from the 90° form and it lengthens the signal if ψ < π/2 and shortens it if ψ > π/2. The results of calculations are compared with the experimentally observed dependences.

The construction of electron-beam-excited semiconductor lasers, their present characteristics, and electron-optics requirements are discussed. The characteristics of laboratory prototypes and of sealed commercially produced laser tubes are given. Potential applications of these lasers in information transmission systems, projection television, metrology, and spectroscopy are reviewed.

An experimental investigation was made of the optical inhomogeneities which appeared in the active medium of a photodissociation laser during coherent emission. The transverse gradient of the refractive index could reach 10^–4 cm^–1. The experimental results indicated that the inhomogeneities were mainly due to gas-dynamic displacements of the working medium and not due to changes in the polarizability of the molecules as a result of photodissociation. Inhomogeneity waves appeared at the walls of a laser cell because of the adsorption of the active gas on the walls. The change in the polarizability of the C₃F₇I molecules in the photodissociation process was estimated. A photodissociation laser with a divergence of the output radiation close to the diffraction limit was built.

A photodissociation iodine laser, employing n-C₃F₇I and i-C₃F₇I molecules, was used in a study of the kinetics of the reactions which accompanied the photolysis of these compounds. The results obtained confirmed the earlier observation that the recombination processes involving iodine atoms in the ground state I(5²P_3/2) had much larger rate constants than those of the corresponding reactions involving excited iodine atoms I*(5²P_1/2). A study was made of the influence of the structure of the radical R, formed by the photolysis of an RI molecule, on the rate constant of the recombination reaction R + R → R₂. The rate constants of several chemical reactions involving iodine atoms and R radicals were determined and the influence of these constants on the energy characteristics of photodissociation lasers was analyzed.

Calculations are given of the instability of the frequency of a laser resonator due to vibrations of its supporting structure. The influence of longitudinal and transverse vibrations of the base is considered. Equations are obtained for the design of a structure which is equally strong in the longitudinal and transverse directions. It is concluded that the most desirable is a structure ensuring that instabilities of the resonator length due to longitudinal and transverse vibrations are equal. It is shown that the optic axis of the resonator should be made to coincide with the neutral axis of the supporting structure so as to minimize the instability of the resonator length and reduce the transverse dimensions of the structure.

The main causes of the explosions of the bulbs of pulse-discharge pump lamps operating under various conditions are analyzed. Empirical expressions are obtained for estimating the maximum flash energy and maximum average power in quartz bulbs of lamps of various types emitting pulses of 10^–2–10^–3 sec duration. An equation is suggested for estimating the combined parameters of the lamp and discharge circuit which should ensure a long service life of lamps emitting pulses of 10^–5–10^–4 sec duration.

An investigation was made of the depth of penetration of a gas discharge into the cavity of a cylindrical cold cathode. This depth was determined as a function of the discharge current (from 5 to 100 mA), the pressure (from 0.62 to 5 mm Hg), and the ratio of the partial pressures of helium and neon (4:1, 6:1, 8:1, 10:1, 12:1). A mixture with the 6:1 ratio was used as an example to demonstrate the method for deriving the empirical dependence of the depth of penetration of the discharge on the factors listed above. The results of life tests indicated that a correct selection of the cathode geometry increased considerably the service life.

The lifetime of the lower active level of a decaying copper plasma laser was determined as a function of the nature and pressure of buffer gases. Pure inert (He, Ne, Ar) and molecular (CO₂, H₂) gases were employed. An equation for the determination of the lifetime of the lower laser level was obtained for self-terminating transitions. It was found that a collisional competition occurred between the transitions corresponding to the yellow and green lines in the spectrum.

The temperature dependence of the output power was determined for a CO laser emitting in the infrared range. The laser action was observed when the discharge-tube walls were cooled with running water. If the mixture contained xenon, the laser action was achieved under continuous-flow conditions and in a sealed laser. The output power of a sealed discharge tube 980 mm long was about 5 W and this value was obtained in tests lasting 80 h.

An investigation was made of the coherent emission from binary solutions of organic compounds pumped by the fourth harmonic of a neodymium laser. Binary solutions of two types were studied: In those of the first type both components readily emitted coherent radiation; those of the second type contained a donor in the form of a nonlasing organic compound with a low quantum efficiency of the fluorescence. A comparison of the experimental and calculated dependences of the laser threshold and emission frequency on the partial concentrations of the donor and acceptor yielded the rate constants of the singlet–singlet transfer of the excitation energy.

An analysis is given of one-dimensional degenerate parametric laser emission of light in a quadratically nonlinear resonator excited by Gaussian pump pulses. The development of the laser action with time is described by the results of a numerical integration of a time series of nonlinear boundary-value problems with suitably selected boundary conditions. Computer-generated "oscillograms" are obtained for the development of the laser action with time. These oscillograms are used in a calculation of the principal laser characteristics and in the optimization of the laser parameters. This method can be used also in calculations concerned with frequency- nondegenerate pulsed parametric lasers.

An investigation was made of the spectral characteristics of a tunable thin-film laser with a distributed feedback. A short-wavelength shift of the frequency tuning range was discovered and studied as a function of the film thickness. The spectral composition of the emitted radiation was determined and it was demonstrated that the H and E waves could be excited separately. It was found that the refractive index of an activated film could be determined from the effective value of this index and from Δλ = λ_H – λ_E.

Single-mode spike-free laser pulse emission was obtained from a CaF₂:Dy²⁺ crystal (λ = 2.36 μ). The time characteristics of the emission were investigated under single-mode and multimode conditions. The number of modes was estimated from the structure of the far-field pattern. The pattern was calculated for a single mode generated in a plane-parallel resonator with a small Fresnel number.

Narrowing of the stimulated emission spectrum was studied using a neodymium-doped niobium-phosphate glass element. Under free-oscillation conditions the linewidth could be reduced to 1.7 cm^–1 when the threshold was exceeded sixfold; this could be done without a significant reduction in the efficiency. The narrowest emission line obtained was 0.15–0.2 cm^–1 wide. This result was achieved by the use of new niobium-phosphate laser glass elements in selective resonators.

An experimental investigation was made of the radial inhomogeneity of the gain and losses, which was one of of the factors reducing the efficiency of the giant-pulse lasers with passive switches. Passive switches with a radial variation of the transmission were suggested and developed. Such switches made it possible to equalize the losses and the gain for rays passing through any point in a transverse section of the active rod. The optimal distribution of the transmission in these switches was determined for ruby rods with lateral surfaces in different states. The use of such Q switches made it possible to increase considerably the laser output power and efficiency.

An internal resonator method is suggested for the determination of the optical density and absorption nonlinearity of matter. The method is based on the change in the Q factor of the resonator due to introduction of an absorbing medium and on the corresponding changes in the rise time and repetition period of laser pulses. Expressions are derived for the calculation of the optical density and absorption nonlinearity. The results are given of a ruby laser investigation of solutions of phototropic substances and of a model plasma with a high concentration of sodium.