Table of contents

A laser utilizing infrared transitions in Xe, operating in the radiation field of a continuously operating nuclear reactor, was constructed and investigated for the first time. The maximum energy characteristics of the laser (specific output energy ~ 0.1 J/liter, efficiency ~ 0.1–0.2% of the energy deposited in the gas) were obtained for a mixture of the Ar:Xe = 100:1 composition at a pressure of 2 atm when the gas was ionized by ²³⁵U fission fragments. The laser could be operated at temperatures up to 650 °C.

A system for pumping wide-aperture excimer lasers was based on compact capacitively isolated Blumlein pulse shaping lines. The use of a single switch with automatic ultraviolet preionization ensured that the laser was simple, reliable, and capable of operation at a high pulse repetition frequency. Laser output energies of 7.6 and 16 J with an efficiency of 1.2% were obtained in XeCl lasers having active volumes of 3.5 and 6.5 liters.

An injection laser with an integrated optical lens was proposed and investigated. The lens was formed by etching a circular recess in the upper emitter layer. A constriction in the laser field distribution indicated generation of diverging waves, typical of unstable resonators.

The Czochralski method was used to synthesize a gadolinium scandium aluminum garnet (GSAG) single crystal activated with chromium (C_Cr = 2 × 10²⁰ cm⁻³), thulium (C_Tm = 8 × 10²⁰ cm⁻³), and holmium (C_Ho = 5 × 10¹⁹ cm⁻³) ions. The luminescence spectra and lasing properties were investigated. The experimental results indicated efficient energy transfer from the Cr³⁺ ions ( ²E and ⁴T₂ states) to the Tm³⁺ ions ( ³F₄ state), fast cross-relaxation sharing of the excitation of the Tm³⁺ ions (³F₄ → ³H₄, ³H₆ → ³H₄), and efficient energy transfer from the Tm³⁺ to the Ho³⁺ ions (³H₄ → ³H₆Tm³⁺, ⁵I₈ → ⁵I₇Ho³⁺). A GSAG:Cr³⁺:Tm³⁺:Ho³⁺ crystal in the form of a rod 4 mm in diameter and 36 mm long (with the length of the illuminated region 31 mm) was subjected to flashlamp pumping resulting in lasing at 2.09 μm. When the reflection coefficient of the exit mirror was R = 75% and the pump pulse energy was 100 J, the output radiation energy was 1.4 J, the differential efficiency amounted to 1.9%, and the threshold pump energy was less than 20 J. Such a laser may be useful in those cases when a high pulse repetition frequency is required.

An experimental investigation was made of a Raman laser emitting picosecond optical pulses from an LiIO₃ crystal (λ_l = 1.143 μm), pumped synchronously by a train of pulses from a phosphate neodymium glass laser with mode self-locking (λ_p = 1.054 μm). The time characteristics of the Raman laser radiation were determined as a function of the mismatch of the resonator lengths. When the resonator lengths were matched, the duration of the output pulses was shortened by a factor of 7 or 8 compared with the pump pulses. In this case, the duration of the output pulses was ~ 1 ps and the energy conversion efficiency was ~ 30%.

An analysis is made of the mechanism of amplification of an electromagnetic wave propagating in a planar waveguide when an electron beam with angular and energy spreads propagates over its surfaces in a magnetostatic field. Numerical estimates are made of the gain in the optical frequency range.

A calculation is reported of selective and nonselective losses in a resonator containing a planar waveguide and reflectors located near the waveguide ends. The conditions resulting in degeneracy of the resonator modes are determined. An analysis is made of the influence of geometric and optical parameters of the waveguide, and of the waveguide–mirror distance on the frequency-selective losses in such a waveguide resonator. The results obtained are compared with corresponding results for resonators containing waveguides of different geometry.

A jet system was used to generate singlet oxygen at a pressure 16 Torr and the concentration of the desired product was at least 60%. The effective probability of trapping of chlorine molecules in a KOH–H₂O₂–H₂O solution decreased on increase in the concentration of KOH and was within the range 10 ^− 3–10 ^− 2. The main factor limiting an increase in the O₂(¹Δ) pressure in such a jet generator was exhaustion of HO₂⁻ on the solution surface.

An experimental study was made of the optical bleaching of organic dyes in liquid and solid (polymer) media during lasing. The results were analyzed by introducing a photostabilization coefficient defined as the ratio of the rates of photodecomposition of the dye molecules in the presence and absence of lasing. Theoretical calculations indicated that the photostabilization coefficient was directly proportional to the stimulated transition cross section at the lasing frequency and to the photon lifetime in the resonator. At the threshold value of the pump power density in the range 0.2–0.5 MW/cm² the photostabilization coefficient reached 2–5, in good agreement with the experimental values of liquid dye solutions. In the case of polymer active media (in contrast to liquid dye solutions) the experimental values of the photostabilization coefficient were systematically lower than those found by calculation, which was due to the absence of stabilization of the population inversion during lasing. An analysis was made of the possible reasons for this effect. The most probable reason was the spectral inhomogeneity of the vibronic transitions in the dyes embedded in a polymer matrix.

The conditions are determined for a long ( l  2 m) 16-mm diameter high-current discharge to be homogeneous. Such a discharge was used to obtain a laser output power of about 100 W as the ultraviolet lines of an Ar²⁺ laser and of more than 350 W as the visible lines of an Ar⁺ laser. The behavior of the active level populations and of the plasma characteristics was investigated as a function of the external parameters of the high-current discharge and conclusions were drawn concerning the influence of different processes on the dynamics of the inverted population variations.

An investigation was made of the radial profiles and temporal relaxation of metastable copper atoms during the interpulse period in a self-heated copper vapor laser. The copper atom concentration in the ground state and the electron temperature, together with their radial profiles and time dependences, were determined from the experimental data. In a copper vapor laser with a 2-cm gas discharge-tube diameter the conditions were sometimes characterized by the presence of a radial electron temperature gradient and also a steady-state distribution of the copper atoms differing from the equilibrium distribution by a deficiency of copper atoms on the axis which arose due to an insufficiently high rate of diffusion of the copper atoms to the central zone from the periphery.

It is shown that an increase in the output energy of an N₂⁺ (B–X) laser (λ = 391 and 428 nm) with electron-beam-controlled excitation is due to suppression of the process of recombination of He₂⁺ ions which competes with filling of the upper active level. The ultimate characteristics of electric-discharge pumping of such a laser are considered.

The results are presented of an investigation of the influence exerted by the inductance and by the storage and peaking capacitances of the LC circuit on the output energy of an XeCl laser. A maximum output energy of 1.5 J was obtained by reducing the peaking capacitance and the inductance to 3.6 nF and 11 nH respectively. The laser output energy doubled when six spark gaps were used instead of one.

A new mode-locking method was used in lasers based on the diffraction of light by a traveling ultrasonic wave. We found experimentally that for a cw pumped YAG:Nd³⁺ laser the proposed method can substantially enlarge the mode-locking band and improve the long-term stability and reproducibility of the duration and repetition period of the output optical pulses.

A report is given of the development and preliminary tests on a system for the excitation of a CO₂ laser pumped by transverse dc discharge. A specific output power 5 kW/m was obtained and there were no electrical power losses in a balanced resistor used in the discharge supply circuit.

It is shown that anisotropic artificial Kerr media are characterized by a high optical nonlinearity and by response times which are two orders of magnitude shorter than those observed for anisotropic materials. These results are in good agreement with a simple model and they demonstrate that an important role in nonlinear properties is played by the intrinsic birefringence of the particles in a material. This may be important in attempts to improve the properties of artificial nonlinear materials.

A theory of optical parametric amplifiers and oscillators is developed in the constant intensity approximation taking into account the reaction on the pump wave phase. Optimization of various parameters such as the length of the nonlinear medium, the reflection coefficient of the mirrors, the wave mismatch, and the intensities of the pump and idler waves was studied to maximize the signal wave gain. Analytic expressions were derived for the resonance phase condition and for the optimal reflection coefficient of the mirrors reflecting the amplified wave.

A theoretical investigation is made of the stability of the fundamental scattering mode in a nonlinear ring resonator under conditions of stimulated light scattering by transmission and reflection gratings. A system of this kind is stable until the stimulated scattering threshold is exceeded by a factor of 3–6. Oscillations of the intensity of the scattered radiation appear above the instability threshold: the period of these oscillations is of the order of the relaxation time of the refractive index grating. It is shown that an increase of the length of a feedback loop can reduce the instability threshold considerably. Moreover, it is demonstrated that the stability range for a transmission grating is narrower than for a reflection grating.

Phase conjugation of radiation in multistage stimulated Brillouin scattering is proposed and implemented. Five reflections with a high (~ 0.95) conjugation parameter for each reflection were achieved experimentally using a three-stage hypersound phase-conjugation system. It was found that as the number of reflections was increased, the pulse developed a spiky time structure. Various systems have been proposed, including a system for obtaining laser beams having their frequency shifted relative to the input radiation by several Stokes shifts and a hypersound four-wave mixing system using reference waves with a large frequency mismatch and various polarization configurations. A system for generating laser beams consisting of two components with parallel wave vectors at frequencies differing by an even number of Stokes shifts was also suggested.

It is shown that there is a set of oscillations with 0.5n(n + 1) periods against the background of a dependence of the efficiency of conversion of laser radiation into n≥2 harmonics that decays monotonically with increasing laser plasma temperature. The electron rest energy reduced by a factor (L / λ) ≫ 1 (L is the characteristic inhomogeneity scale of the plasma density, λ is the wavelength of the laser radiation) serves as the characteristic scale of the periods, which are an algebraic function of the harmonic number. In a hot laser plasma (T > 1 keV) with an inhomogeneity scale L = 50 μm exposed to the action of neodymium laser radiation, the flux density of the third harmonic oscillates with a period of the order of 0.5 keV.

Spectral and mass-spectroscopic diagnostics were used to investigate expansion and interaction with a rarefied background gas (Xe at a pressure of 10 ^− 5–10 ^− 1 Torr) of a laser plasma formed by the interaction of Nd laser pulses (10¹¹ W/cm²) with a plane target made of aluminum. Spectral diagnostics was performed using the line radiation emitted by the laser plasma and by the background (Al III, Al II, Xe II). An investigation was made of the spatial distribution of the laser plasma and background ions and of the influence of charge transfer on this distribution. The spatial distribution of the intensity of the Al II radiation had two maxima corresponding to the front of the Al III ions and the slower Al II component. This behavior of the Al II ions was due to Al²⁺ + Xe→Al⁺ + Xe⁺ charge exchange in the laser plasma front, which was one of the stages of a cascade of charge-transfer transitions involving highly charged Al^z+ ions interacting with Xe. Mass-spectroscopic results confirmed fully this scheme of kinetic processes near the laser plasma front.

An investigation is reported of the propagation of electromagnetic radiation in a layer-periodic structure formed in a disturbed surface layer of cadmium sulfide subjected to electron and optical annealing. This structure has a period of d₀ = λ / 2n₁ and is due to annealing of the disturbed material (during the first pulse) in the vicinity of the intensity maxima in an interference pattern and also due to the difference between the refractive indices of the disordered phase n₁ and the "perfect" material n₀. The intensity maxima in a layer-periodic structure are located outside the regions annealed during the first pulse. This increases the volume of the annealed regions from one pulse to the next. Annealing of the whole disturbed layer can be achieved simply by displacement of the recrystallization front by ~ d₀, since the displacement should occur in each of the periods. The structure period d₀ is close to that at which the nontransmission effect is observed. This leads to anomalies of the distribution of the intensity I(x) in the structure. A quasiperiodicity is exhibited by I(x) and the quasiperiod is considerably greater than d₀, whereas the intensity at the maximum may be considerably greater than the intensity of the incident wave, which enhances the effectiveness of annealing of the internal regions.

Theoretical and experimental investigations were made of a four-wave interaction of middle-infrared radiation based on a thermal nonlinearity of absorbing liquids and gases. A study was made of the influence of parasitic effects associated with heating of a nonlinear medium (such as the thermal lens effect, frequency sweeping of interacting waves, thermal expansion of the medium, and convection) on the efficiency of the four-wave interaction and the quality of phase conjugation utilizing this interaction. The conditions under which this influence is minimal were identified. An experimental study was made of phase conjugation of CO₂ laser radiation by a four-wave interaction in CCl₄ with a high reflection coefficient (up to 20% in the cw regime). The attained phase conjugation was limited the thermal lens effect, but this could be compensated.

An account is given of a photoemission mechanism of generation of a current and of a "fast" component of a spontaneous magnetic field as a result of interaction of laser radiation with a metal surface. The key feature of the proposed theory is an allowance for the magnetization of a conducting aureole and for an inhomogeneity of illumination of the metal target by the radiation emitted from an erosion jet. Analytic expressions are obtained for the magnetic induction near the surface and for the current on the surface in the cathode region. A comparison is made with the experimental results.

A model is proposed and used to consider the interaction of an optical radiation pulse with an aerosol active medium (finely dispersed metal particles) in a resonator. It is shown that one can determine the basic parameters of the aerosol active medium more accurately than previously.

An investigation was made of modulation of the phase and polarization of modes in a few-mode fiber waveguide subjected to axial deformation. The simplest and most convenient (for analysis) controlled interference pattern was obtained on addition, at the exit from a waveguide, of the fields of two modes of different order or of components of two orthogonally polarized waves of the same mode when an additional phase shift between these waves was induced by deformation. The two investigated schemes were suitable for the construction of simple and highly sensitive sensors capable of detecting small strains with characteristics which could be varied by suitable selection of the waveguide parameters and of the signal processing method.

A comparison was made of the calculated and measured radiative losses suffered by the fundamental and first higher modes in real waveguide structures with a depressed cladding. It was found that in determination of the operating range of single-mode waveguides with a depressed cladding it is essential to allow not only for the increase in the losses due to leaking of the fundamental HE₁₁ mode at long wavelengths, but also for the shift of the cutoff wavelength of the first higher HE₂₁ mode for shorter wavelengths.

Theoretical and experimental studies were made of the effects of a distributed magnetooptic interaction in fiber waveguides. Analytic solutions were obtained for relating light modulation at the exit of a waveguide to the parameters of its winding in the form of a coil and to an external magnetic field under conditions ensuring the exact spatial phase matching. It was confirmed experimentally that the interaction length of the order of several tens of meters was quite acceptable and could ensure a sensitivity of at least 10 ^− 4 Oe in the case of a quartz fiber waveguide.

Characteristics of a traveling-wave electrooptic light modulator, controlled by a microwave power amplifier, were investigated. The input control power was 7.5 mW in the modulation frequency range 4–5 GHz. Optimization of the modulator characteristics made it possible to reduce the control power to 2–3 mW at 4–5 GHz and to less than 10 mW at 9–11 GHz.

An investigation was made of a traveling-wave integrated optical modulator utilizing a microstrip electrode structure and tunnel-coupled channel waveguides formed in Ti:LiNbO₃. The modulator characteristics were as follows: the half-wave voltage was 10 V (at a wavelength of 1.3 μm), the working frequency bandwidth was at least 4 GHz, the dynamic range (for a laser radiation power of 5 mW) was about 40 dB, and the level of the higher harmonics (at 1 GHz) was 35 dB.

A theoretical analysis is made of the influence of the coating on the optical properties of a metal with a periodic relief of its reflecting surface. A system of equations is derived for the diffraction of light by a rectangular periodic relief of a metal surface with a three-layer coating. These equations apply to arbitrary depths of relief, any layer thicknesses in the coating, and any relief period. Analytic expressions for the diffraction efficiency are obtained and analyzed in some specific cases of interest.

An investigation was made of a cooled prism deflector of the transmission type made of a DKDP crystal. The problems of thermal stabilization of crystals and elimination of the influence of piezoelectric deformations of the crystal on the operation of the deflector, as well as protection of the surfaces from damage and attainment of both large angles of deflection and a large number of resolved elements were tackled. A special immersion liquid capable of retaining its properties down to – 70 °C was developed. The use of this liquid made it easier to achieve high deflection angles and to protect surfaces. An angle of deflection of ~ 4° was obtained in a field of 20 kV/cm, which ensured that up to 350 elements were resolved when the beam diameter was 5 mm and the wavelength was λ = 1.06 μm. The deflection angles could be increased by using a series of consecutive deflector cells and by bipolar control of these cells. The ultimate potentialities of the deflectors were estimated from the number of the resolved elements.

A theoretical investigation is reported of a two-dimensional focusing of an atomic beam by a centrally symmetric optical field formed by two pairs of mutually perpendicular laser beams. Conditions under which this optical field acts as a converging laser lens are identified. The errors of such a laser focusing system are determined.

Bleaching of amorphous silicon films by local heating with a focused laser beam was found to provide a promising optical storage method useful in the fabrication of half-tone optical masks needed in the fabrication of optical diffraction components. A study was made of changes in the optical properties and the structure of a-Si films occurring under the influence of laser radiation. A spatial resolution up to 2000 lines/mm was achieved. A mechanism explaining the experimental results was developed.

Determination was made of the composition of the YAG:Cr:Tm:Ho active medium capable of pulse-periodic (10 Hz) emission of 2-μm stimulated radiation. An average output power of 7.5 W was obtained in the case of free-running operation and 0.5 W when single pulses were emitted. The loss factor was determined for 2-μm radiation in quartz fiber waveguides 0.4 mm in diameter: its value was 5%/m.

A description is given of an active optical system utilizing a copper vapor laser with a hemispherical resonator for projection processing of objects. This analysis ended with transfer of an image to a surface. The unevenness of the edge of the processed regions was within the range 0.4–0.8 μm.

An experimental study was made of the influence of cw CO₂ laser radiation on gas-adsorption chromatography of SF₆, CH₂Cl₂, and BCl₃. Resonant excitation of molecules by laser radiation did not alter the duration of their retention in a chromatograph column. A reduction in the retention time was attributed to nonresonant heating of the column walls by laser radiation.