Table of contents

Stimulated emission from an oxygen–iodine laser with a photodissociation source of excited oxygen O₂(¹Δ), based on ultraviolet photolysis of ozone, was observed for the first time. The ozone photolysis products, particularly O(¹D) atoms, had an unfavorable influence on the lasing parameters. A study was made of the possibility of using CO₂, N₂, and N₂O gases as effective agents for quenching of O (¹D). An output energy ε = 0.8 mJ/cm³ and an efficiency of energy transfer from the O₂(¹Δ) molecules to iodine atoms amounting to η = 41% obtained for a mixture of the composition characterized by the ratio CF₃I:O₃:SF₆:He:N₂O = 0.055:0.45:11:21:6 Torr were close to the corresponding values reported for an oxygen–iodine laser with a chemical generator of O₂(¹Δ).

Experimental and theoretical investigations were made of self-diffraction of CO₂ laser radiation in absorbing nematic crystals. A considerable increase in the signal-wave gain occurred as a result of transfer of energy from the pump radiation near a nematic–isotropic liquid phase transition (in this case the absolute gain of a weak infrared wave reached 600%). A theoretical interpretation of the effect was based on a model of a thermal nonlinearity of a nematic liquid crystal near the phase transition.

It is shown that the wavefront of a relatively weak light beam can be controlled by a wavefront corrector in a feedback loop and this leads to phase modulation of the original optical field and to a considerable reduction in the optical load on the corrector.

The results are presented of investigations of the physical mechanisms of pumping and stimulated emission from a C₂D₂ laser pumped optically by CO₂ laser radiation. Studies were made of the energy, time, and spectral characteristics. The pump source was a pulse-periodic CO₂ laser emitting at the frequency of the 9R (12) line. Stimulated emission was obtained at frequencies of 562.5 and 499.7 cm ^− 1 with energies of ~ 100 and 5 mJ, respectively. At 562.5 cm ^− 1 the average power was ~ 5 W in the pulse-periodic regime at a repetition frequency of ~ 100 Hz and the pulse power reached ~ 0.5 MW. These parameters make it possible to use a C₂D₂ laser for separation of isotopes, particularly Ti isotopes by selective multiphoton dissociation of TiCl₄ molecules.

A study was made of the feasibility of obtaining λ = 585.3 nm stimulated emission from a Penning laser utilizing a mixture of Ne and H₂ excited by an electron beam generated by an open discharge. A quasi-cw output power of 2.5 W with an efficiency of 0.1% in terms of input energy was obtained in a cell 0.7 cm in diameter and 7.2 cm long. The maximum gain was 5.7 m ^− 1. The optimal ratio of components was p_Ne:p_H2 = 1:4 at a total pressure of 2.6–3 kPa, which differed from the conditions in discharges with a "hard component" and hollow-cathode discharges. Experiments using pairs of pump pulses showed that the laser could be converted to cw operation.

A semiconductor injection laser with optical and optoelectronic feedback loops was investigated. Active mode locking of such a laser resulted in generation of picosecond light pulses at a repetition frequency dependent on the ratio of the signal transit times in the optical and optoelectronic feedback loops. The results indicated that it should be possible to construct a compact self-contained source of ultrashort light pulses without recourse to sophisticated electronic equipment.

An experimental investigation was made of the amplitude-frequency characteristics of a rotating YAG:Nd³⁺ ring laser with a nonlinear absorber made of LiF:. The spiking instability of lasing was suppressed by an active negative feedback loop which created losses of the counterpropagating optical waves in proportion to the sum of their intensities. It was established that in the case of free lasing and under active mode-locking conditions the feedback loop made it possible to increase considerably the permissible value of the initial absorption coefficient and of the intensities of the counterpropagating waves at which the spike fluctuations were still absent. Strong self-diffraction of the counterpropagating waves in the nonlinear absorber eliminated completely the competitive suppresion of one of the waves when the difference between their frequencies was increased. Consequently, this rotating solid-state laser with the nonlinear absorber characterized by a short relaxation time was capable of stable generation of beats in a wide range of frequency differences between the counterpropagating waves.

Variation of the length of an external resonator resulted in continuous tuning of the emission frequency in a range of 60 GHz, exceeding the intermode spacing (21 GHz) by a factor of 3. This was attributed to a dependence of the refractive index on the electron density. The line width did not exceed 6 MHz.

An investigation was made of the energy capabilities of an electron-beam-controlled Ar–Xe laser at active mixture pressures in the range p = 1–4 atm. Under pulse-periodic conditions a reduction in the pressure from 4 to 1 atm caused a drop in the specific output energy from 1000 to 180 W/liter. An analysis was made of the influence of air impurities on the laser energy characteristics.

An investigation was made of an electric-discharge XeCl laser consisting of a narrow-band master oscillator and an amplifier with an unstable resonator. Narrow-band radiation tunable in the 307.5–308.5 nm range with a line width of up to 1 pm and an angular divergence of 0.1 mrad was obtained. Up to 70% of the laser output power was concentrated in a narrow line.

Lasing was induced in Y_1.5Er_1.5Al₅O₁₂ (λ = 2.94 μm) crystals by selective pumping of the electronic–vibrational wing of the ⁴I_15/2–⁴I_13/2 transition. A population inversion was established in this YAG:Er³⁺ laser by a strong interaction between the excited Er³⁺ ions at the ⁴I_13/2 level and the transfer of energy from the lower active level to the upper one in accordance with the ⁴I_13/2–⁴I_9/2, ⁴I_13/2–⁴I_15/2 scheme.

A comparative study was made of amplification of radiation emitted from YSGG:Cr:Nd, YLF:Nd, and YAG:Nd crystal lasers in a single-pass amplifier utilizing LGS-32 phosphate glass. The results indicated that a YSGG:Cr:Nd crystal laser was a promising master oscillator for the use in combination with phosphate glass amplifiers.

Lasing was observed in a system with self-pumped "loop" phase-conjugate mirrors in YAG:Nd³⁺, KGW:Nd³⁺, and GSGG:Cr³⁺:Nd³⁺ active media. An investigation was made of the threshold, energy, spectral, and temporal characteristics of the output radiation under lasing and regenerative conditions.

Packet pulsed operation of a semiconductor streamer laser was achieved at pulse repetition frequencies up to ~ 10 MHz. The average power of the output radiation was ~ 10 mW (for CdS), which was between two and three orders of magnitude higher than the published values. A high-power compact laser with these parameters was constructed.

It is shown that the characteristics of a continuous-flow gas-discharge CO₂ laser can be calculated by reconstructing the volume distribution of the discharge power from the experimentally determined field of the unsaturated gain. A comparison is made of the calculated field of the radiation intensity and of the output power of the laser with experimental results.

An investigation was made of a calcium molybdate single crystal activated with neodymium and a considerable anisotropy was found in its spectral and lasing properties. In the pulse-periodic regime an active element 4 mm in diameter and 55 mm long receiving a pump energy of 22.5 J at a repetition frequency of 50 Hz yielded an output power of 12 W at the wavelength of the ordinary wave λ_O = 1.061 μm.

An investigation was made of an XeF laser with an active length ~ 170 cm and an exit aperture of 12 × 20 cm. The optical pump source was a single-channel sectioned electrical discharge on the surface of polyethylene with a period-average deposited power density dP / dx ~ 41.6 MW/cm. The energy of the laser radiation generated as a result of the B–X transition (λ ≈ 351 nm) reached 70 J, whereas in the visible range the energy delivered by the C–A transition (λ_av = 480 nm) was 98 J.

An investigation is reported of the structure of the eigenmodes of a parametric ring oscillator utilizing stimulated Brillouin scattering in a region of self-intersection of a signal light beam in a nonlinear medium. A study is made of the influence of nonreciprocity of a feedback loop, due to nondegeneracy of a four-wave interaction, on the lasing threshold and on the quality of optical phase conjugation near the threshold. It is shown that the phase conjugation quality and the structure of the scattered beam can be controlled by varying the coefficients representing spatial compression of the signal beam and the phase shift between the signal and scattered waves in the feedback loop.

Experimental and numerical investigations were made of the change in the frequency during an output pulse from a CO₂ laser. It was found that the distribution of the density in the CO₂ medium differed considerably from the results of calculations based on earlier theoretical models and this was due to inhomogeneous heat evolution. A good quantitative agreement was achieved between numerical and experimental dependences of the frequency drift of the output radiation for different parameters of the active medium and of the resonator.

An analysis was made of a method of measuring the ground-state population of copper atoms in the medium of a self-heated copper vapor laser. The active medium was probed using radiation from a pulsed dye laser (temporal resolution 5 ns, spatial resolution 2 mm). An investigation was made of the ground-state kinetics during an excitation pulse and in an interpulse interval over the whole lasing temperature range of 1350–1650 °C in a commercial UL-101 laser. A deficit of copper atoms additional to the thermal one was revealed and studied using the radial distributions of the ground state population. The physical processes governing the radial distributions of copper atoms in the ground state are discussed.

Calculations were made of the kinetics of a transient He–H₂ plasma excited by an electron beam formed in a discharge. The kinetic plasma relaxation model took into account 155 plasma-chemical reactions. An analysis was made of the time dependences of the plasma parameters, the concentrations of the 3 ³S and 2 ³P active levels, and the specific output power due to the λ = 706.5 nm He transition at pressures of 8 and 15 Torr in an He:H₂ = 2:1 mixture and pump frequencies of 100 and 200 s ^− 1. The main mechanisms determining the population of the active levels and their temporal dynamics were identified. A comparison between the results of the calculations and the experimental data showed that the population inversion and lasing conditions agree with the model of a plasma recombination laser with the Penning depopulation of the lower active levels.

Absorption probing was used to study the dynamics of the population of the ^1.3∑_u⁺ lower excimer states of the Xe₂* molecule in the active medium of a high-pressure high-power Ar–Xe laser utilizing the 5d–6p transitions in the Xe atom. The first direct experimental evidence was obtained showing that electron beam excitation pumped the upper active levels in the discharge beginning from excited states of the active gas rather than from the ground state. Accumulation of the sum of excited and ionized Xe states in the discharge plasma was observed experimentally for the first time.

Coupling between linear sections of waveguides in a laser Y-junction array alters the threshold conditions for the excitation of the array supermodes and preferential formation of an optical field with a two-lobe far-field distribution.

An analysis is made of the competition between vibrational–rotational transitions in a CO₂ laser with superimposed fields of two waves in a resonator, for example, in a widely used laser with an autocollimating diffraction grating. The results are reported of experimental and theoretical investigations of the combined lasing zone when switching occurs between the lines. A good agreement between the experimental and theoretical results is obtained.

An experimental study was made of the characteristics of the operation of an NH₂D laser (λ = 506 μm) when its active medium was subjected to an alternating electric field. It was found that saturation of the absorbing transition in the active molecule was lifted and this was manifested by an increase in the intensity of the output radiation of the laser in the presence of the modulating electric field, reduction in the threshold pressure of the working gas, and lowering of the pump power. The dependences of the relative increase in the intensity of the output radiation, observed in the presence of the modulating field, on the amplitude of this field and its frequency, and on the pressure of the working gas were determined.

The emission spectra of a laser plasma were determined at wavelengths of 6–7 and 7.5–8.5 Å for flat targets with atomic numbers Z = 6–83 using laser radiation of densities (1–4) × 10¹³ W/cm². The experimentally determined intensities of the K, L, and M spectra (~ 10¹⁵–10¹⁶ photons/4π) were compared with the results of calculations of conversion of laser radiation into x-ray emission of a laser plasma. The results obtained made it possible to optimize a laser-plasma source of soft x rays, which could be used in particular as an x-probe of a high-temperature dense plasma.

An experimental investigation was made of the processes of interaction of radiation from an XeCl excimer laser (λ = 308 nm, τ = 20 ns) with aluminum. The threshold of formation of an erosion plasma in vacuum (q _* = 200 MW/cm²) was independent of the number N of the pulses. The threshold q _* in air depended strongly on N and could fall to 70 MW/cm², due to the formation of a strongly absorbing layer on the target surface. The depth of the layer removed by radiation of intensity q ≈ 1 GW/cm² could reach 1 μm per pulse. The average optical thickness of a plasma created by one pulse was of the order of 0.3 at λ = 308 nm. Evaporation by XeCl laser radiation increased the aluminum absorptivity by a factor of 3–5. The erosion plasma temperature did not exceed 2 eV for q ≈ 1 GW/cm². A general energy balance was determined for the laser radiation–target–plasma in vacuum.

An investigation was made of the damage to "organic glasses" (transparent polymers) by laser radiation applied for duration t_p ≈ 10 ^− 3–1 s. Beginning from t_p ≈ 5 ms, the probability p of damage to polymethylmethacrylate (PMMA) ceased to rise on increase in t_p and even began to fall in the range t_p > 20 ms. Thermal self-defocusing of laser radiation was observed in PMMA, polystyrene, and polycarbonate. Theoretical estimates of the characteristic defocusing time, considered as a function of the parameters of the laser pulses and of the material, were obtained and checked experimentally. Constants which could be used as quantitative criteria of the importance of defocusing were obtained for PMMA and polystyrene. A fall of the dependence p (t_p) observed in the range t_p  20 ms was attributed to defocusing, but this explanation did not apply to an inflection at t_p ≈ 5 ms.

A rigorous analytic theory is provided of laser generation of a periodic surface relief by photochemical etching of semiconductors in the case of slight heating of the surface, and also by pyrolytic surface etching reactions and deposition of films absorbing laser radiation. Calculations are reported of increments of an exponential growth of dominant structures with time, and of their periods and orientations as a function of the intensity, angle of incidence, and polarization of the incident radiation, and of the parameters of the treated surface. Theoretical results are shown to agree well with all the available experimental data.

The thresholds of bulk damage of commercially available ultraviolet-transparent MgF₂, CaF₂, and LiF crystals were determined for λ = 248 nm KrF laser radiation incident in the form of pulses of 70 ns duration. The dependences of the damage thresholds of these crystals on the focal spot diameter were obtained for this diameter from 8 to 1600 μm.

An experimental investigation was made of the formation of a plasma in the evacuated interior of a spatial filter containing a metal stop. An estimate was obtained of the plasma formation threshold at which the filtered radiation of a CO₂ electron-beam-controlled laser was screened. This effect appeared already after 5 μsec from the beginning of lasing when the edge of the stop was irradiated with a pulse characterized by an energy density exceeding 500 J/cm².

A bent dielectric waveguide with a continuous profile of the complex refractive n_c is investigated. It is shown that a negative perturbation of the real part of n_c can reduce the losses in a bent waveguide. For a given radius of curvature and given parameters of the medium there is an optimal width of a planar waveguide layer for which the losses are minimal. It is shown that the properties of straight and bent waveguides of this type are different.

It is shown that the problem of investigating the mode composition of a partly coherent radiation beam in a randomly inhomogeneous medium can be reduced to a study of evolution of the energy of individual modes and of the coefficients of correlations between the modes. General expressions are obtained for the coupling coefficients of modes in a parabolic waveguide with a random microbending of the axis and an analysis is made of their evolution as a function of the excitation conditions. An estimate is obtained of the distance in which a steady-state energy distribution between the modes is established. Explicit expressions are obtained for the correlation function in the case when a waveguide is excited by off-axial Gaussian beams or Gauss–Hermite modes.

An account is given of the characteristic features of the linear and quadratic electrooptic effects in a deformed fiber waveguide. A model is proposed to account for suppression of the center of symmetry in a fiber waveguide by bending, which results in macroanisotropy and lifts the restrictions on the linear electrooptic effect. The light-guiding properties of the fiber impose certain restrictions which follow from the spatial phase-matching conditions that have to be satisfied before the linear and quadratic electrooptic effects are observed. An agreement between the theoretical and experimental results confirms the correctness of the selected model.

An acoustooptic interaction was investigated in a film waveguide made of zinc oxide deposited on a thermally oxidized silicon substrate. Diffraction of laser radiation by Sezawa surface acoustic waves in the resultant multilayer waveguide structure was much stronger than that by quasi-Rayleigh waves. The acoustic and optical parameters of the structure were determined, including the acoustooptic coupling coefficients.

A study was made of the optimal conditions for coupling a laser beam (λ = 1.3 μm) with a slight ellipticity of its transverse cross section into a single-mode fiber waveguide. The coupling was performed by a hemispherical microlens formed from a cone-tapered end of a fiber waveguide. The maximum coupling efficiency achieved in these experiments was 78%, against the theoretically possible value of 89%. A fiber-optic module enduring rigid stable connection of a laser to a single-mode fiber waveguide was constructed.

A description is given of a procedure used in numerical solution of the self-consistent problem of finding the radiation field and thermoelastic deformations of rectangular mirror sheets in a telescopic resonator of a continuous-flow gas-discharge CO₂ laser. The results obtained are compared with the case when the resonator mirrors are undeformed. An analysis is made of the mutual influence of the radiation and thermal distortions of the mirrors, and of the effects of these distortions on the divergence of the output beam of such a laser.

A new miniature head of a fiber probe for a laser Doppler velocimeter is proposed. A special feature of the probe is the presence of a wavefront divider in the form of a bilens. Analytical relationships are obtained between the parameters of the velocimeter under optimal alignment conditions. A report is given of an experimental study of the operation of a fiber velocimeter. A study is made of the influence of the mode composition of the radiation in the fiber waveguide on the characteristics of the probe field. Experimental evidence shows that it is possible to adjust the period of the interference field in the course of velocity measurements.

A study was made of isotopically selective multiphoton dissociation of 2,2,2-trifluoroethanol (CF₃CH₂OH) by radiation from a pulsed TEA CO₂ laser. Enrichment of the dissociation product CO with ¹⁸O was observed. The maximum selectivity a ≈ 7.2 ± 1.5 and the dissociation yield of the target product (CF₃CH₂¹⁸OH) β₁₈≈5% were obtained when the laser radiation frequency was ω_las = 1029.44 cm ^− 1 and the energy density was Φ ≈ 1.8 J/cm². The degree of conversion of oxygen atoms from CF₃CH₂OH to CO was 50% for Φ = 1.8 J/cm² and u ~ 90% for Φ = 2.0 J/cm². The multiphoton absorption coefficients and the energy absorbed, on the average, by one 2,2,2-trifluoroethanol molecule were determined. Estimates were obtained of the energy needed to separate one ¹⁸O atom, which was ~ 12 keV.

An analysis is made of the possibility of preliminary correction of the shape of mirrors for the purpose of compensation of optical inhomogeneities developing in a laser-active medium during pumping and stimulated emission. Specific calculations are reported for multipass CO amplifiers with the Cassegrain optics. It is shown that for pulse durations comparable with the time needed for the formation of pump-induced optical inhomogeneities of the active medium a small (up to 1%) change in the curvature of mirrors in a Cassegrain telescope makes it possible to reduce by a factor of 5–6 the average (during a radiation pulse) beam divergence at the amplifier exit compared with the case of strictly cylindrical (or spherical) mirrors.

Thermal sensitization of photographic emulsions was used to record holograms in the infrared and submillimeter parts of the spectrum. Photographs were recorded on a FT-101 specialist film using CO₂ laser radiation and were reconstructed using He–Ne laser radiation. The results demonstrated that thermal sensitization of silver halide emulsions could be used to record submillimeter radiation and in submillimeter holography.