Table of contents

Sources of coherent radiation can be developed on the basis of layered superconducting compounds. These sources are tunable over a broad frequency range. Their energy characteristics are close to those of semiconductor lasers. A model of single crystals of layered high T_c superconductors is discussed. It is assumed that the layers are coupled with each other by a Josephson tunneling of electrons. As electromagnetic radiation is generated by the current of electron pairs, the electron tunneling occurs under the conditions of the time-varying Josephson effect, under the influence of two voltages: a static voltage applied to the superconducting layers and an alternating voltage induced by the field excited in the system.

We have investigated the spatial, temporal, and spectral characteristics of a XeF laser in the visible region (0.48 μm) and the UV region (0.35 μm). We have determined experimentally the dependence of the output energy on the vapor pressure of the original XeF₂ gas for various configurations of the optical pumping source and various resonator Q factors. Output energies of 117 and 174 J, respectively, were achieved on the C–A and B–X transitions of the XeF molecule, with internal efficiencies of 2.6% and 3.6%. We studied the directivity of the output from the XeF (C–A) laser as photolysis waves of various shapes were generated in the active media. The output wavelength in the visible region of the spectrum can be tuned. We investigated the emission characteristics of segmented high-current open surface discharges as a function of the rate of energy deposition in the plasma in the working medium of the XeF laser.

We investigated the spectral characteristics of an SF₆–HI–H₂ laser pumped by an electron beam. The time-integrated output spectrum was studied as a function of the composition of the hydrogen-containing component of the working mixture. Lasing takes place under conditions far from rotational equilibrium.

We have experimentally implemented the following laser-oscillator scheme for a Ti:sapphire laser system: mode-locked operation of an Nd:YAG laser, stimulated-Raman-scattering (SRS) pulse compression in SF₆, frequency doubling in a KDP crystal, and copropagating SRS in hydrogen. This system transforms a single 30-ps pulse at a wavelength of 1.06 μm with an energy of 3 mJ into a 300-fs pulse at 0.76 μm with an energy of 100 μJ.

We investigate the linewidth of an AlGaAs/GaAs C³ injection laser. The linewidth is a strong function of the injection currents of the laser section and the modulating section and also the size of the gap separating the two. At optimum tuning the linewidth is smaller than that of a corresponding plane-resonator laser.

We have investigated lasers oscillating on atomic transitions of xenon and pumped by a radially converging electron beam with pulse lengths between 0.07 and 0.1 ms. We have determined experimentally the dependence of the threshold beam current density and the output spectrum on the Q-factor of the laser resonator. We have shown that for beam current densities smaller than 16 mA/cm² and for a pulse length ~ 0.1 ms there is a quasisteady lasing at wavelengths λ = 1.73, 2.65, 2.03, and 2.63 μm if the resonator output mirror and the mixture composition are chosen appropriately. We have also observed simulatenous oscillation on the following pairs of lines: λ = 1.73 and 2.03 μm, 2.03 and 2.65 μm, and 2.65 and 2.63 μm. When the lattice supporting the foil covering the beam window was cooled with water, periodic-pulse operation at a repetition rate of 5 Hz was achieved in a laser with a pumped volume ~ 18 liters.

The position of the light pulses on the period of the modulating function has been measured as a function of the discharge current, the resonator length, and other parameters for an argon laser with active mode locking. These measurements were carried out for various emission lines in the visible and UV regions. At a minimum pulse length, and at a pump level well above the threshold for lasing, the losses in the mode locker are high. The reasons for the difficulties encountered in attempts to achieve simultaneous mode locking of the 488.0- and 514.5-nm lines are pointed out. The evolution of the pulse shape (from the point of appearance to the point of disappearance) as the basic laser parameters are varied has been studied. The pulses are at their shortest when there is a satellite, rather than under single-pulse conditions. The experimental data are consistent with a model of supermodes.

A study has been made of how a static external electric field affects the output of a stimulated-Raman-scattering laser using compressed hydrogen. The external field substantially influences the energy distribution among the higher-index components of the stimulated emission. At a qualitative level, this effect can be explained on the basis that a dipole moment is induced in the hydrogen molecule and that a transition from the first vibrational level to the ground state becomes allowed.

Luminescence spectral properties and lasing characteristics of ethanol solutions of several 7-diethylaminocoumarins, recently synthesized, have been measured. Specifically, the peaks in the absorption and luminescence spectra, the fluorescence yields, the lasing efficiency, the peak in the lasing spectrum, and the lasing region were measured. When solutions of these dyes are used as laser active media it becomes possible to tune the output wavelength continuously over the spectral interval 450–505 nm. The compounds have a fairly high lasing efficiency.

A panoramic absorption spectrum of the plasma of a He/Sr laser at the time of the maximum discharge current has been measured by time-resolved absorption spectroscopy. The spectral resolution was no worse than 0.003 nm. Anomalously broad bands (about 0.5 nm wide) are found in the interval 613–645 nm. The absorption kinetics in these bands is correlated most closely with, for example, the population kinetics of the 4²F_7/2 state of the strontium ion. It is suggested that the most probable source of these bands is an absorption accompanying bound-free (or free-bound) transitions of (HeSr⁺)* or (SrSr⁺)* molecular ions or HeSr excimer molecules. The absorption kinetics of certain states of He*, Sr, Sr*, Sr⁺, and Sr⁺* is also described in qualitative terms.

An intense two-photon-excited luminescence has been observed in the UV region in several scintillators. The characteristics of this luminescence vary in a nonlinear way with the intensity of the exciting light. A transition from spontaneous luminescence to superluminescence occurs in polycrystalline stilbene samples.

Parametric excitation of stimulated Brillouin scattering in a system of intersections of a signal wave with an intense pump beam can be used for phase conjugation of weak light beams with a high reflectivity ( ~ 10⁵).

We have conducted an experimental study of phase conjugation of microsecond laser pulses via forward Brillouin scattering in the field of two intersecting pump beams whose transverse structures closely resemble that of a single mode. We have demonstrated that an interaction can take place at relatively low pump power densities. It thus becomes possible to achieve phase conjugation of long pulses without competition from thermal self-effects.

We have investigated backward stimulated diffusive scattering of light with a time-varying speckle structure by photorefractive crystals in which the nonlinearity mechanism is diffusion-driven. We show that the efficiency and conjugated fraction for this process depend on the ratio of the coherence time to the dielectric relaxation time of the medium.

The space-time processes that take place in a Fabry–Perot interferometer containing a complex, optically nonlinear medium have been studied. A realization of such an interferometer based on a metal-insulator-semiconductor-(liquid crystal) (MIS-LC) structure and a corresponding mathematical model are discussed. Spatial phenomena in a Fabry–Perot interferometer with a built-in MIS-LC cell are also discussed.

We have measured the reflection coefficients and threshold pump energies for phase conjugation via stimulated Brillouin scattering (SBS) in various chemical compounds and binary solutions. We have studied the possibility of controlling the parameters of SBS phase conjugation by purely chemical means.

We find the theoretical threshold for phase conjugation of a pump beam with speckle structure by a double photorefractive phase conjugate mirror based on transmitting and reflecting gratings of a diffusion type. For a speckle beam the nonlinear dependence of the profile of light-induced optical nonuniformity on the local intensity profile reduces the readout efficiency and raises the threshold by as much as a factor of 1.5.

We investigate the phenomenon of self-diffraction in optically dense media for those cases where it is necessary to take into account the inverse effect of the medium on the field. Our study is based on a numerical analysis of the Maxwell–Bloch equations. This analysis reveals that, as the concentration of two-level systems increases, an anomalous response of four-wave mixing arises. This response is associated with the appearance of a self-diffraction signal in the negative-delay region and also with a faster decay of coherence in the system.

We have succeeded in generating the second harmonic of the radiation from a DF laser for the first time, using single crystals of ZnGeP₂. For crystals with lengths of 10.1 and 13.6 mm, the overall external efficiencies of the entire oscillator system were 4 and 6.2%. The internal efficiencies of second-harmonic generation in the crystals were 7.6 and 11.8%, respectively.

We show theoretically and experimentally that the optimum geometry for phase conjugation of speckle beams in a loop containing a photorefractive crystal is the "biting-its-own-tail" geometry with beam diameter preserved. We predict an increase in the threshold for the process by a factor of 1.5 due to the introduction of speckle in the beam to be conjugated.

A laser structure consisting of two active films on a common substrate with a higher refractive index is proposed. The films are coupled by radiation modes through their common substrate. Dispersion curves are found for such structures. The distance over which there is a complete pumping of energy from one waveguide to another is found as a function of the substrate thickness. Generation has been achieved in a structure consisting of two polymethyl methacrylate films activated by the dye rhodamine 6G on a lithium niobate substrate with two external mirrors.

A new method for producing light pulses with an ultrahigh repetition frequency is proposed. The method is based on counterpropagating four-wave mixing in an optical fiber. The information is coded at low repetition frequencies, and the pulse train is compressed in time. The effect would be to raise the repetition frequency to 10¹¹–10¹² Hz.

Signals proportional to components of the gradient of the sharpness function can be generated by optical methods. A numerical simulation indicates that this approach would be effective in work with low light fluxes, for which quantum detection effects are important.

A "dispersionless" multiple-beam interferometer with a small distance between mirrors is described. The phase characteristics of the mirrors are chosen in such a way that the resonance condition depends only weakly on the frequency of the light, while a high sensitivity to displacement of the mirrors is retained. It thus becomes possible to significantly relax the requirements on the spectral width and frequency stability of the laser light source.

The higher spatial harmonics of the photorefractive response have been studied theoretically and experimentally for gratings written by phase-locked detection in an alternating external field. The conditions for writing higher spatial harmonics are derived analytically. The amplitude of the second spatial harmonic has been found experimentally as a function of the spatial frequency in two Bi₁₂TiO₂₀ crystals.

The resistance to laser damage and the microhardness of a composite material based on a polymer and a porous glass have been studied. The microhardness is good, and the damage resistance high. The characteristics of a passive Q switch fabricated from this material are reported.

The tensor properties of χ⁽²⁾ gratings written in bulk glass have been studied for various polarization conditions. Three basic cases were studied: the writing of gratings by waves with parallel polarizations, perpendicular polarizations, and polarizations making an angle of 45°. The results indicate that a static electric field proportional to (EE)E is written.

Coulomb broadening in a three-level system is studied. Interference resonances are not broadened by collisions, differing from saturation resonances in this regard. Experimental spectra of generation on adjacent ion transitions and resonance fluorescence are interpreted. An increase in the output power of ion Raman lasers is predicted.