Table of contents

An analysis is made of the characteristics of erasable recording media intended for optical data storage, including thermomagnetic media used in disk memories. A new class of optoelectronic media based on multilayer structures is considered. It is shown that the density of the data recorded in such media can reach 10⁵ bit/mm² and the energy of an optical write pulse need not exceed 10⁻¹² J. The use of such media is opening up extensive opportunities for optical programming and redundancy. The rate of exchange of data in an optoelectronic storage device can reach 10¹¹ bit/sec.

A theoretical investigation was made of the evolution of the radial gradient of the refractive index of the active medium in a photodissociation iodine laser amplifier of nanosecond pulses utilizing slow pumping. Two mechanisms were taken into account in discussing the appearance of an optical inhomogeneity in the medium: the excitation of acoustic waves in the laser cell during pumping in the interior and near the walls. It became clear that the amplitudes of both waves could be made to pass through a minimum simultaneously by choosing the composition of the active gaseous medium. It was concluded, on the basis of the results obtained, that if the pulse being amplified is applied at this moment of time there will be a negligible deterioration in the focusing of the beam.

The specklon theory methods are used to calculate the diffraction efficiency and intramodulation noise of volume holograms of speckle fields allowing for saturation of the photoresponse. It is shown that 100% diffraction efficiency can be achieved if the depth of the light-induced phase modulation of the reconstructing wave is at least 10 rad. Saturation of the photoresponse reduces the relative level of the noise if the ratio of the intensities of the object and reference waves used in recording a hologram is less than 0.5.

An investigation was made of thermal nonlinearity of the lasing process in an atmospheric-pressure electron-beam-controlled CO₂ laser having an unstable resonator. Experimental and theoretical results are given of an investigation of the optical quality of the active medium and of the field structure in the near-field and far-field zones during a lasing pulse. Good agreement is obtained between the calculated and experimental data.

An investigation was made of a gadolinium scandium gallium garnet laser activated with Cr³⁺ and Nd³⁺. A stimulated Brillouin scattering mirror and a plasma switch made it possible to vary the duration of the pulses emitted by this laser within wide limits. Compression of light pulses as a result of stimulated Brillouin scattering in CCl₄ reduced the Stokes pulse duration to ∼0.5 nsec, which was close to the theoretical limit.

It is shown that there are no fundamental limitations on the sensitivity, which might be associated with the wave nature of the radiation, of amplitude sensors made from multimode graded-index waveguides and the limitations found in practice are solely due to the fact that the optimal measurement procedure cannot be realized. The different sensitivities of modes in a graded-index waveguide to external perturbations make it possible to construct amplitude sensors with a tunable sensitivity. It is shown that, in principle, it is possible to increase exponentially the sensitivity of amplitude sensors by creating periodic longitudinal inhomogeneities in a graded-index waveguide and by using an active graded-index waveguide. A description is given of interference sensors made from multimode graded-index waveguides operating in conjunction with computer-synthesized spatial filters selecting the required superposition of modes. The sensitivity of such sensors is estimated.

An analysis is made of nondegenerate four-wave interaction (FWI) in a resonant medium (two-level model) with Doppler line broadening allowing for nonlinear absorption of the weak radiation. The cubic approximation with respect to the field is used to derive expressions for the coefficients of parametric coupling and absorption of the mixed waves. The angular dependences of the reflection coefficient are studied for quasicollinear and orthogonal FWI geometries. It is shown that, as a result of the thermal motion of the particles, the dependence of the reflection coefficient on the angle θ between the interacting waves results in considerable limitation of the angular width of the reversed beams. This limitation is greater for degenerate FWI. In the case of nondegenerate FWI, as a result of the selective action of waves on groups of atoms having a specific velocity projection, the reversal efficiency may increase on increase in θ.

A theoretical study is made of a linear, in respect of the field of lower frequency (signal), transient double resonance in a system with a shared upper level. The radiation of higher frequency (pump) is selected to be a 2π pulse which is spectrally much narrower than the contour of the Doppler scatter of the frequencies of a transition which is in resonance with this pulse. A condition is found for the appearance of a signal pulse of constant profile moving at the velocity of the pump pulse and growing exponentially in the course of its propagation into a resonant medium. It is shown that in general the energy of a signal pulse depends nonmonotonically on the energy of the pump pulse: there is an optimal value of the pump energy at which the rate of rise of the signal energy is maximal. A study is made of the efficiency of a double resonance on the detuning from a resonance in the pump and signal channels.

An O₂(¹Δ)–N₂–iodine aerosol mixture is proposed as an active medium of a pulsed oxygen–iodine laser. It is shown that the lifetime of the stored energy in this mixture may be comparable with that in an iodine-free O₂(¹Δ)–N₂ medium. After a certain induction time, as a result of self-heating, the mixture is converted into an active oxygen–iodine medium by an explosive process.

An analysis is made of a thermophysical model of a chemical singlet-oxygen generator. It is shown that at the exit from a thermally insulated reaction vessel, the water vapor content is approximately three times the oxygen content. Calculations are made of the water vapor content when the solution is cooled and circulated through the reaction vessel. As the total pressure is increased, the efficiency of purification of the oxygen in a water vapor condensation trap deteriorates strongly. This is one of the reasons for the degradation of the active medium of a cw oxygen–iodine laser with increasing oxygen pressure. For a trap comprising a smooth tube and a thermally insulated reaction vessel, the trap radius R and the oxygen pressure at the exit p'_O2 should satisfy the condition p'_O2R<12 Torr, so that the laser active zone contains less than 10% of water vapor and no less than 50% of O₂(¹Δ). The oxygen pressure range can be increased by cooling the solution in the reaction vessel.

Theoretical and experimental investigations were made of the statistics of photocounts of modulated laser radiation transmitted by a turbulent atmosphere. Experimental measurements were made for three types of modulation: rectangular, sawtooth, and sinusoidal. Theoretical calculations were carried out for the first two types of modulation on the assumption that the modulation period is considerably greater than the sampling time of the counting unit. A comparison of the experimental and calculated results showed that the calculated curves describe quite well the experiments.

A range of discrete logic elements for purely optical data processing systems (optical computers) was constructed utilizing optical bistability in vacuum-evaporated thin-film interferometers with an intermediate ZnS or ZnSe layer. Operation of optically programmed components of a processor, of triggers of various types, and of relaxation oscillators (timers) was demonstrated.

A theoretical study is made of the evolution of the shape of corrugations that form on the surface of germanium and silicon as a result of interaction with laser radiation. It is shown that an allowance for the electrodynamic nonlinearity results in a change from an exponential growth of a periodic structure and establishes limits on the depth of surface corrugations. An increase in the energy carried by laser pulses and in the number of pulses broadens the spectrum of the periodic structure and the period corresponding to the maximum corrugation depth changes compared with the value corresponding to a surface plasmon resonance. The profile of the periodic structure becomes distorted by a structure with half the initial period. The small difference between the predicted maximum corrugation depth and that found experimentally is a demonstration of the dominant role of the electrodynamic nonlinearity in the formation of periodic structures on germanium and silicon surfaces as a result of interaction with laser radiation.

The formation of a spectrum of fast electrons in a laser plasma in the presence of multiple interactions with resonant fields is considered. The suppression of the generation of fast electrons when a target is irradiated by a multimode laser is discussed. The formation of fast electrons due to their multiple reflection from the boundary of an expanding plasma is analyzed.

An analysis is made of the feasibility of measuring the components of the nonlinear susceptibility tensor by observing oscillations of the second harmonic intensity as a function of the frequency of the converted signal. It is shown that if the dispersion of the refractive indices is known, the components of the nonlinear susceptibility can be measured with the same accuracy as that obtained using Maker's fringes. This method is less sensitive to the quality of the samples and to the divergence of the optical beam. Measurements were made of the components of the nonlinear susceptibility tensor of various molecular crystals.

An investigation was made of the characteristics of mirrors for a high-power cw argon laser operating in the visible range. The mirrors were made by three different methods, namely by thermal resistive sputtering, by electron-beam evaporation, and by cathode sputtering. For the best samples, the scattering coefficients were 0.04–0.1% and the absorption coefficients were 0.02–0.03%, independently of the method used to make them. The optical strength was not directly related to the scattering and absorption in the coatings, but depended on the method of preparation. Cathode-sputtered mirrors were found to have the best operating qualities in high-power cw argon lasers. The question of thermal focusing of a laser due to surface absorption in the exit mirror is discussed.

An investigation was made of the time dependence of light-induced separation of a mixture of isotopic modifications of ¹³CH₃F–¹²CH₃F molecules formed as a result of vibrational excitation of CH₃F molecules by CO₂ laser radiation. Measurements were made in a wide range of gas pressures. The experimental results are compared with the theory of the effect.

A study was made of the efficiency of a luminescence optical filter made of glass activated with divalent europium ions. This filter was used in a neodymium glass laser. An improved variant was developed for calculating the filter efficiency, which made it possible to determine the filter-induced relative change in the threshold pump power E_th and in the energy of the output radiation from the spectral characteristics of the filter–active medium system and from the excitation conditions. A satisfactory agreement was achieved between calculated and measured values of these quantities. The use of such a filter in neodymium lasers containing GLS glasses of types 21, 22, 23, and 24 and KGSS7 glass reduced E_th sometimes by a factor of 1.5–2, which made it possible to enhance the laser efficiency by a factor of 1.7 (to 2.5%). In an ideal case of total transfer of the energy absorbed by the filter to the active element the laser efficiency could rise to 4%.

An analysis is made of the main laws governing the propagation of opposite waves in a randomly inhomogeneous medium with a cubic refraction nonlinearity with respect to the field, allowing for interference. It is shown that, in spite of modulation of the optical intensity as a result of interference between the opposite waves, almost complete bleaching of a heterogeneous medium can be achieved for fairly large scattering particles. An analysis is made of an optical resonator filled with a randomly inhomogeneous nonlinear medium and the conditions for bistability are determined. It is established that a considerably lower Q factor than in similar devices using nonlinear absorbers is sufficient to achieve bistability in this resonator.

A study is made of adaptive compensation of phase distortions in a randomly inhomogeneous medium when an unknown object of arbitrary shape is observed in coherent light. Maximization of the sharpness functions is used for this purpose. A sharpness function is proposed in which an object is illuminated by a field with a known distribution of the amplitude and phase, and maximization of the function is independent of the shape of the object. An analysis is made of secondary extrema and it is shown that for a large signal/noise ratio there is a maximum corresponding to compensation of distortions of the medium. The suggested practical adaptive scheme does not require significant modifications of the existing systems.

A study was made of holographic recording of volume phase gratings in dichromated gelatin films designed for operation in the grazing incidence case. The special properties of grazing diffraction by volume phase gratings were analyzed. The diffraction efficiency achieved in this way was ∼30% when the angle of incidence was 88°.

An investigation was made of photostimulated absorption of light in chalcogenide glass fibers when a side surface of a fiber was illuminated with unresolved (white) or monochromatic light. It was found that such additional illumination of fibers with low-intensity (∼2×10⁻⁶ W/cm²) monochromatic light of photon energy lower or higher than the optical band gap increased the absorption by the fiber material. The results were interpreted by charge exchange between localized states due to intrinsic or impurity defects.

Pulse-periodic operation was attained in multicell semiconductor lasers made of ZnO, ZnSe, CdS, and GaAs crystals. At room temperature of the active element when the pulse repetition frequency was 50 Hz and the pulse duration was 8 nsec, the following values of the average radiation power were achieved for the first time: 25 mW (ZnO), 22 mW (ZnSe), 125 mW (CdS), and 90 mW (GaAs). Replacement of the active element provided means for discrete tuning of the emission wavelength. These output powers were achieved using a compact portable electron gun.

An experimental comparison was made of intracavity and heterodyne methods of reception of weak optical signals. The efficiencies of the two reception methods were compared over a 200-m atmospheric path at the optical signal wavelength of 10.6 μ. The efficiency (signal/noise ratio) was the same for both reception methods, but the sensitivity was higher in the intracavity case. It was also found that signal fading, observed in the intracavity reception case due to fluctuations of the optical path length, could be readily compensated in the case of phase modulation by ensuring a sufficiently wide reception pass band.

Single-mode fiber waveguides with two and four identical weakly coupled channels in a shared quartz cladding were developed. Specific features of these waveguides were conservation of the mutual coherence of the radiation in the channels, identical orientation of the birefringence axes in diametrically opposite channels, and azimuthal dependence of the relative phase shift in the channels as a result of lateral deformations. These properties made it possible to construct simple systems for a number of fiber-optic sensors of strain, pressure, velocity, etc.

A comparison is made between the multiphoton excitation of OsO₄ molecules containing a natural mixture of Os isotopes and similar excitation of ¹⁸⁷OsO₄ in a gasdynamic molecular jet using an infrared multifrequency laser field. It is shown that the highest isotopic selectivity and the best parameters of the multiphoton excitation process are achieved by using three-frequency excitation.

The dynamics of an optical discharge in argon maintained by CO₂ laser radiation was studied as a function of the focusing angle. The characteristics of the growth of stable and unstable discharges were determined. The positions of the optical discharge boundaries were compared with calculations based on published theoretical models.

An analysis is made of the method of collimation of soft x rays from a laser plasma and the experimental results obtained by this method are reported. Collimation was achieved by propagation across a planar waveguide structure formed by plane-parallel glass plates coated by chromium films and separated by a gap of 200 μ.

The observation of stimulated emission in the ultraviolet due to C II and C IV transitions in an electric-discharge plasma interacting with a flat barrier is reported. The results of measurements of the gain are presented.

An investigation is made of the transmission of InAs under conditions of propagation of two opposite waves. It is shown that the opposite wave induces nonlinear absorption with an efficiency 1.5 times higher than that of the wave whose transmission is measured, i.e., when analyzing nonlinear absorption of opposite waves in InAs, coherent effects must be taken into account.

A study was made of the properties of fused single-mode biconical couplers fabricated in a high-frequency electric discharge. A multiplexer–demultiplexer was constructed for the first time with an interval of 1.5 nm between the channels, channel isolation of 20 dB, and excess losses of 0.2 dB. Continuous adjustment of the characteristics of this fused demultiplexer was possible.

Efficient simultaneous stimulated emission of any two lines in different 00⁰1–10⁰0 (02⁰0) and 00⁰2–10⁰1 (02⁰1) sequence bands in a TEA CO₂ laser was achieved. This was based on the separation of two orthogonally polarized waves. It was demonstrated experimentally that the spectral, energy, and temporal parameters of the two-wave lasing regime can be controlled over a wide range.

A pulsed singly resonant optical parametric oscillator was constructed from an LiNbO₃ crystal. Narrow-band radiation from a cw He–Ne laser (λ = 3394 nm) was injected into an extracavity wave when the oscillator was pumped with multimode radiation from a Q-switched YAG:Nd laser. Narrowing of the spectrum of the parametric oscillator to the width of the pump wave spectrum was observed and this was accompanied by an increase in the conversion efficiency in the oscillator by a factor of 1.5–2.

Stimulated emission of 200-μsec pulses was achieved in the red due to the 3p[1/2]₁–3s[3/2]₁ (λ = 724.5 nm) and 3p[1/2]₁–3s[3/2]₂ (λ = 703.2 nm) transitions in a neon atom when an He–Ne–Kr mixture was excited by an electron beam. The resonator and the mixture composition were optimized. The maximum efficiency was ∼0.3% for λ = 724.5 nm. The gain was ∼3×10⁻³ cm⁻¹ at both wavelengths and the distributed loss factor was ∼2×10⁻⁴ cm⁻¹ for λ = 724.5 nm and 9×10⁻⁴ cm⁻¹ for λ = 703.2 nm.

It is shown experimentally for the first time that the Raman-induced Kerr effect spectroscopy can be used in a remote measurement system when the probe wave is formed in the medium under study as a result of Rayleigh and Mie scattering of one of the pump waves. The panoramic spectrum of a strong Raman band of ethanol was obtained in the 3000–2800 cm⁻¹ range.