Table of contents

An investigation was made of the radiation emitted by argon mixed with nitrogen and excited by a high-power proton beam. The results indicated that amplification in this mixture was possible as a result of np'–4s and np–4s' (n = 5–7) transitions because of clearing of the 4s levels by resonant transfer of the excitation energy to a nitrogen molecule. Lasing was observed as a result of a transition in Ar I at λ = 344.3 nm.

A new family of entirely solid-state tunable quasi-cw sources of picosecond and femtosecond laser radiation was developed on the basis of the principle of nonlinear frequency conversion and dispersive compression of the spectral continuum.

An investigation was made of the characteristics of radiation generated by a copper vapor laser operating in the superradiant regime and having a single convex mirror. An LG-201 commercial sealed active element was used, together with an experimental element having a discharge channel longer by a factor of 1.4. Highly stable radiation was obtained with characteristics which could be controlled by changing the mirror radius. For mirror radii two or three orders of magnitude smaller than the distance from the mirror to the exit aperture of the active element, the divergence angle of the beam was close to the diffraction limit. Average radiation power densities of 1–10 MW/cm² could be achieved in a focal spot. This is more than two or three orders of magnitude higher than those obtained in a plane–plane resonator. The energy per pulse, the peak power, and the axis of the radiation pattern were several times more stable than for an unstable resonator, and the intensity distribution in the focal plane was also more uniform. These advantages should improve the quality of high-precision materials processing.

An investigation was made of a ring laser with a parametric feedback based on four-wave mixing in the active medium of a pulsed CO₂ laser. Dependences of the output energy on the gain in a CO₂:N₂ = 1:1 gas mixture at pressures of 0.1–0.4 atm and on the pulse profile were obtained. The laser radiation power reached 1 MW. Some compensation for phase distortions inside the laser resonator was observed.

Injection locking of a semiconductor laser by external radiation is investigated. Equations describing a locked laser are derived and solved allowing for emission of spontaneous radiation and excitation of stray modes. An analysis is made of the stability of steady-state solutions. It is shown that incorrect results are obtained if a locked laser is analyzed in a single-mode approximation and spontaneous emission is ignored in the case of positive frequency detuning. Inclusion of stray modes reduces permissible values of the phase shift between the injected and own laser radiation, and gives rise to an asymmetry of the dependence of the phase shift on the detuning. The dependence of the output power on the injected power is used to find the spontaneous emission factor. Experiments are reported in which the output power sometimes exhibits fluctuations in the locked state.

Q-switching in a flashlamp-pumped yttrium scandium gallium garnet crystal, activated with chromium, thulium, and holmium ions (YSGG:Cr:Tm:Ho), resulted in emission of the TEM₀₀ mode because of the ⁵I₇→⁵I₈ transition in Ho ions (λ = 2.088 μm) at room temperature. When the pump energy was 80 J and the repetition frequency was 1 Hz, a giant TEM₀₀ pulse with an energy of 50 mJ was generated.

An optical system was developed for a laser utilizing YSGG:Cr:Nd and YSGG:Cr:Tm:Ho active elements in the resonator emitting at two wavelengths, 1.06 and 2.088 μm, under free-running conditions. Energies of 0.8–1.25 J (λ = 1.06 μm) and 0.35–0.4 J (λ = 2.088 μm) were achieved for a total pump energy of 200 J from two flashlamps.

Whisker PbTe crystals 70–120 μm in diameter were used as injection lasers with two p-n junction geometries: transverse and coaxial. Lasing was observed in the pulsed regime at T = 4.2 K (λ = 6.5 μm). The mode structure of the emission spectra was difficult to control because electrical and optical quality of whisker crystals was not sufficiently high. Total internal reflection modes and isotropic angular distributions in the p-n junction plane were observed for the transverse diodes.

A study was made of the operation of a Q-switched CO₂ laser in the range 9.171–10.808 μm of the second harmonics with wavelengths 4.585–5.404 μm, and also of the operation of a CO laser in the range 5.427–5.849 μm. The emission spectra were investigated by automatic time scanning with the aid of a diffraction grating and a rotating mirror, both placed inside the resonator.

Simultaneous emission of two wavelengths, λ₁ = 1.064 μm and λ₂ = 1.318 μm, from a cw solid-state YAG:Nd³⁺ laser was achieved and studied experimentally. It was demonstrated that the spatial and amplitude characteristics of the λ₂ radiation could be controlled by modulating the losses of the λ₁ radiation. It was established that the stability of the radiation power at the two wavelengths could be enhanced by introduction of nonlinear losses. The emission of two cw series of pulses at wavelengths λ₁ and λ₂, and tuning of their relative delay was achieved.

A new chromium ytterbium erbium laser glass LGS-Kh was used for the first time in minilasers emitting at 1.54 μm and characterized by a very low (less than 5 J) threshold and a relatively high (up to 1.7%) efficiency. An average output power of 0.7 W was obtained at a pulse repetition frequency of 7 Hz.

A bleaching-wave laser (utilizing an ether solution of coumarin 6 and 1,4-diphenylbutadiene) was pumped by a flashlamp-type source utilizing magnetoplasma compressors. When the bleaching wave propagated in the solution at a velocity of ~ 1 km/s, cw lasing was obtained for 30–40 μs with an output energy of 1.2 J in the 517 ± 5 nm range. Estimates were made of the threshold pump intensity and of the internal losses in the bleaching-wave laser. It was found that, compared with a laser without a bleaching wave (utilizing an ethyl solution of coumarin 6), a bleaching wave improved greatly (under the same excitation conditions) the output energy and the directionality of the radiation.

Analytic expressions are derived for the optimal density of dye molecules in a solution for a bleaching-wave laser and for the optimal exit mirror transmission required to maximize the stimulated emission efficiency using monochromatic and nonmonochromatic pumping. These expressions are used as the basis to estimate the efficiency and specific lasing energy of a bleaching-wave laser utilizing an ether solution of coumarin 6 and 1,4-diphenylbutadiene.

An analysis is made of the influence of quenching of excited iodine on the parameters of stimulated enthalpy scattering in iodine photodissociation lasers. It is shown that the stability of the active mixtures of these lasers during evolution of stimulated scattering by thermal waves may be improved by selecting a suitable quenching agent and a suitable concentration.

An analysis is made of the influence of the "hole burning" effect on the optical bistability during operation of lasers containing a saturable absorber in the resonator. The rate equation approximation is used to examine single-mode and multimode lasing. The results obtained show that under certain conditions not only the bistability, but also multistable states can appear.

Investigations were made of the spectral, fluorescence, and lasing characteristics of 2-iminocoumarin derivatives. It was established that proton donor solvents have the strongest influence on these characteristics. The structure factor also has a substantial effect. In specific interactions of the molecule the attachment of the diethylamino group in position 7 results in changes in the nonradiative deactivation of its electronic excitation. The characteristics of the solvate effects of iminocoumarins identified can not only increase the spectral tuning range of an active medium utilizing these coumarins, but can also enhance appreciably the efficiency of flashlamp-pumped lasers.

An investigation was made of the influence of the effects of wave refraction by turbulent pulsations of the gas flow on the characteristics of the wavefront and on the angular divergence of radiation emitted from a plane-parallel optical resonator. The equation for the mutual coherence function Γ (x, x'; z) was solved numerically in the approximation of a parabolic equation with Markov (in terms of the longitudinal correlation radius) fluctuations of the permittivity. The calculations were carried out using the method of splitting by parameters. It is shown that enhancement of the turbulence flattens out the distribution of the field on the mirror and increases the angular divergence. When the angular divergence is governed by turbulent effects, the magnitude of this divergence increases also on increase in the wave number.

It is shown that long radiation pulses needed in applications of lasers in technology may be emitted efficiently by an oxygen–iodine chemical laser. Slow photolysis can increase the output pulse duration to approximately 1 ms while retaining a high efficiency. Calculations yield the dependence of the lasing characteristics on all the parameters of interest. It is demonstrated that at high active medium pressures (up to 100 Torr) and low iodine concentrations, the pulse duration may be regulated with a high specific output energy and a high photolysis efficiency.

The gain was determined for a D₂–CO₂–Ar mixture excited by a non-self-sustained discharge initiated by an electron beam. At low CO₂ concentrations (from 1 to 3 %) the gain ranged from 0.4 to 0.8 m ^− 1. The maximum specific energy which could be deposited in the mixture without disturbing its homogeneity amounted to 400 J · liter ^− 1 · atm ^− 1.

An investigation is made of the possibility of stabilization of phase-locked operation of a set of lasers as a result of nonlinearity of the refractive index of the active medium.

An investigation was made of fiber-optic devices as components of resonator optics of semiconductor lasers. The example of the Mach–Zehnder and ring interferometers is used to demonstrate the effectiveness of the fiber-optic methods in mode discrimination and narrowing of the emission line. An investigation is reported of a semiconductor laser emitting at λ = 1.58 μm and of an external fiber resonator utilizing resonant Rayleigh scattering in a ring fiber interferometer. The laser emission line width is shown to decrease by a factor of at least 2 × 10³. The mechanism of reduction of frequency fluctuations by Rayleigh scattering in a ring interferometer is considered.

An analysis is made of the excitation kinetics of the active medium of a TEA CO₂ laser using different theoretical models: a temperature model, either taking into account or neglecting anharmonicity in the ν₃ modes of CO₂ and N₂, and a model taking into account the level kinetics in the ν₃ modes of CO₂ and N₂. A comparison is made of the results of a calculation with the experimental dependence of the laser output energy on the specific input energy in the range up to 2 J/cm³. The calculated and experimental data are found to agree for a vibrational temperature model taking anharmonicity into account and using a relatively high value, known from the literature, of the constant of the intramode exchange in nitrogen, and for a model taking into account the level kinetics and assuming accumulation of strong relaxants of the upper active level.

Measurements were made of the absolute quantum yields of I(²P_1/2) atoms, Φ_I* (λ), in the photolysis of C₂H₅I and C₃H₇I in the λ = 240–290 nm spectral range. It was established that nonadiabatic processes influence the values Φ_I* (λ).

Experimental results provide evidence of the possibility of using KRS5 and KRS6 crystals for acoustic Q switching of a CO₂ laser of average power. It is proposed to employ these materials as the acoustic line of an intracavity acoustooptic modulator of the refraction type in order to realize low-frequency modulation of the output radiation from a waveguide CO₂ laser.

A semiclassical system of equations is derived in the two-wave approximation describing the dynamics of evolution of cooperative Raman scattering (CRS). Relaxation and parametric processes, inhomogeneous broadening effects, and propagation processes are taken into account. An investigation is made of the influence of parametric processes and progagation effects on the CRS process. Strong amplitude and phase modulation of the scattered field pulses is predicted. A continuous transition from CRS to quasisteady-state stimulated Raman scattering is described.

Quartz glass fiber waveguides suffer not only from a transverse optical inhomogeneity but also from a transverse inhomogeneity of a hypersonic wave responsible for stimulated Brillouin scattering (STBS). Experiments on such waveguides revealed a considerable broadening of the STBS spectrum (compared with a homogeneous nonwaveguide medium) in the case of a single-mode waveguide characterized by antiwaveguide propagation of hypersound, i.e., when the velocity of hypersound in the core was higher than the velocity in the cladding. The width of the STBS spectrum depended weakly on the duration of the pump pulses and was governed by the nature of the transverse hypersonic inhomogeneity. The best agreement between the experimental results on the width of the spectrum and theoretical calculations was obtained for a waveguide with a central dip in the refractive index profile. Determination not only of the width but also of the profile of the STBS line yielded more detailed information on the refractive index profile.

Efficient generation of the second harmonic of CO₂ laser pulses was achieved in GaSe single crystals at repetition frequencies up to 100 Hz. The phase-matching angles were measured for GaSe at pump wavelengths of 9.3, 9.6, 10.3, and 10.6 μm. The threshold power densities for surface optical damage and for the formation of a plasma jet on the surface of GaSe were determined. The efficiency of second harmonic generation in a GaSe crystal 0.65 cm thick was up to 9%. A comparison was made of GaSe and ZnGeP₂ crystals as materials suitable for the generation of the second harmonic of CO₂ laser radiation.

Spectral dependences of reflection in a degenerate four-wave interaction of CO₂ laser radiation in resonant SF₆, CF₃Br, and CD₄ gases were investigated with a spectral resolution of 5 × 10 ⁻² cm ^− 1. A structure associated with one- and two-photon vibrational transitions in the gases was observed in the spectra. High reflection coefficients (of some tens of percent) were achieved by optimizing the phase conjugation conditions whilst maintaining the resonant character of the reflection.

A theoretical analysis is made of the efficiency of typical ring systems of phase-conjugating mirrors utilizing a degenerate four-wave interaction in media with a thermal nonlinearity. The analysis is made for steady-state conditions taking into account wave saturation effects in an amplifier situated in a positive feedback circuit. It is shown that the reflection coefficient in these systems is extremely sensitive to the level of the phase-conjugate signal (as the ratio of the signal intensity to the saturation intensity of the amplifier active medium is increased, the reflection coefficient of the ring phase-conjugating mirror decreases sharply). It is also found that at a high level of the nonlinearity and for an appreciable gain per pass, these systems exhibit multistability (i.e., several different steady states exist).

A description is given of a new approach to an analysis of the statistics of fluctuations of stimulated scattering which are due to the noise nature of spontaneous radiation. The approach is based on amplification of spontaneous noise in a given excitation field under conditions of stimulated Brillouin scattering (STBS) and on a statistical analysis of noise fluctuations by two methods: in real time and after a fixed time delay when the number of realizations is large. A report is given of experiments carried out at T = 300 K in long single-mode glass fiber waveguides where a transverse distribution of optical fields could be controlled rigorously and kept constant throughout the zone of interaction between the waves. An exponential distribution of the stimulated scattering intensity was established, indicating constancy of the exponential statistics of fluctuations of the intensity of spontaneous radiation in the course of its amplification. This made it possible to calculate the STBS emission spectrum. A determination of the STBS gain increment demonstrated a good agreement between the theory and experiment. A time relationship established between the pump intensity spectrum and the emission spectrum made it possible to find the relaxation time of hypersound in a glassy medium.

Waves of switching between steady and transient (periodic and stochastic) states of a nonlinear ring interferometer are discovered and investigated. Pulsating spatially inhomogeneous distributions are found in the range of existence of a periodic state.

An approximation of a constant intensity of two counterpropagating noncollinear waves in a ring system is used to consider phase conjugation as a result of a four-beam interaction in a medium with a transient nonlinear response. An analytic solution is obtained of a system of equations for weak waves consisting of an arbitrary set of quasiplane components. It is shown that when the absolute instability threshold is exceeded by a nonlinear phase shift, the maximum increment is exhibited by those components which are inclined at a certain angle to the phase-conjugate wave. The conditions for reliable phase conjugation by introduction of a phase screen into the ring are identified.

A four-wave mirror exhibiting a thermal nonlinearity was used in a study of the interaction of concurrent waves under parametric feedback conditions in the presence of a nonreciprocal element. Strong reflection of a series of pulses of ~ 300 ns duration from a neodymium glass laser was demonstrated: the maximum reflection coefficient was in excess of 30. An analysis was made of the quality of the radiation reflected from this four-mirror parametric feedback system. A considerable reduction was observed in the steady-state threshold for the operation of this mirror with a thermal nonlinearity when the angles of convergence of the interacting beams were small compared with the case of head-on collision of the waves.

A model is proposed to describe the generation of sound when a dielectric liquid evaporates under the influence of laser radiation. It is confirmed that explosive boiling is possible and methods for experimentally detecting it are discussed.

A theoretical and experimental investigation was made of the excitation of elastic vibrations when optical radiation of high power density interacts with the surface of a solid body. It is shown that the characteristic wavelength of the acoustic waves which are then formed is determined by the radius of curvature of the inelastic region and not by the crater diameter. As a consequence, natural vibrations of a massive irradiated sample can be excited with the laser beam focused down into a relatively small spot.

It is shown that the nature of convective motion in a thin layer of a liquid formed by local heating of a metal surface by laser radiation depends not only on the temperature gradients, but also on the presence of trace impurities in the liquid, particularly of surface-active substances (surfactants), which can alter radically the nature of convection. The results are given of an experimental study of a change in the nature of convection as a result of addition of surfactants during melting of metal samples by radiation from industrial cw CO₂ lasers.

An investigation was made of the near-ultraviolet part of the spectrum of radiation from a plasma created by irradiating a solid target in a low-pressure gas (0.5–15 Torr) with CO₂ laser radiation of intensity up to 0.1 TW/cm². During excitation of a buffer gas by a shock wave, spatially selective emission of individual spectral lines with excitation energies of 35–60 eV was observed. The radiation formed a hemispherical halo of radius which was a function of the intensity of the laser heating radiation and of the buffer gas pressure. The halo was due to spatial localization of the ions with the highest charge multiplicity generated in a shock wave excited in the gas near the target heated by laser radiation.

The emission spectra of a laser plasma formed from tungsten were determined in the ultrasoft x-ray range (photon energy 60–130 eV) when the power density of the laser radiation was 30 GW/cm² (ruby laser) of 5 and 2 GW/cm² (XeCl lasers).

A probe investigation was made of a surface plasma created by CO₂ laser pulses with different time profiles. When a target was irradiated in air or in vacuum by a train of short (τ = 2.5 ns) pulses, it was found that the nature of evolution of the profile of the recorded current changed on increase in the energy density. Experiments in vacuum showed that the change from a smooth single-mode pulse to a train of nanosecond pulses of the same energy reduced considerably the energy thresholds of plasma formation and increased the amplitude of the plasma-induced current. Current pulses from the target were recorded up to the end of interactions with laser radiation.These pulses were attributed to cumulative effects due to the annular shape of the irradiation zone.

The results are given of calculations of the parameters of an unstable ring resonator with an internal angular selector based on a Fourier phase corrector. It is shown that the use of such a selector makes it possible to compensate partly for the effects of small-scale phase inhomogeneities and to reduce also the influence of the edge diffraction on the structure of the field in a resonator.

Theoretical and experimental investigations are reported of new mode optical components (elements) which are analogs of sinusoidal phase diffraction gratings with a variable modulation depth. Expressions are derived for nonlinear predistortion and depth of modulation, which are essential for effective operation of amplitude and phase mode optical components in devices used for analysis and formation of the transverse mode composition of coherent radiation. An estimate is obtained of the energy efficiency of phase and amplitude mode optical components, and a comparison is made with the results of an experimental investigation of a set of phase optical components matched to Gauss–Laguerre modes. It is shown that the improvement in the energy efficiency of phase mode components, compared with amplitude components, is the same as the improvement achieved using a phase diifraction grating, compared with amplitude grating with the same depth of modulation.

The method of laser Raman spectroscopy was used to study heterophase water systems. The apparatus included an argon laser, an optical multichannel analyzer, and a microcomputer. The temperature dependences of the profiles of the valence (stretching) band in the Raman spectrum of liquid water between + 50 °C and – 7 °C and of polycrystalline ice Ih (from 0 to – 62 °C) were determined, as well as the spectral polarization characteristics of the Raman valence band. A method was developed for the determination of the partial concentrations of the H₂O molecules in liquid and solid phases present as a mixture. An analysis was made of the errors of the method and the sources of these errors. Applications of the method to multiparameter problems in more complex water systems (for example, solutions of potassium iodide in water) were considered. Other potential practical applications of the method were discussed.

A two-beam spectrometer utilizing injection lasers emitting in the near infrared was constructed. The spectrometer utilizes rapid scanning of the laser emission frequency followed by recording with an analog–digital converter. The spectrometer parameters are as follows: a spectral resolution of at least 2 × 10 ⁻³ cm⁻¹, a response time 50 ns, and a detectivity amounting to 0.0003% of the incident power carried by one pulse.

A description is given of a method for determination of the optical losses in a waveguide using a waveguide resonator in which the difference between the paths of interfering beams is altered by varying the emission wavelength of a single-frequency semiconductor laser. The measurements made on lithium niobate waveguides yielded the losses of 0.6 dB/cm at the rate of change of the laser emission frequency when the pump current was altered at a rate of 1.3 GHz/mA.

The method of finite elements is used in a calculation of the field of thermoelastic stresses in two-channel single-mode fiber waveguides with identical cores located symmetrically in a shared quartz glass cladding. An analysis is made of the dependences of the stresses on the distances between the cores and of the influence of ellipticity of the cores on the magnitude and nature of the stresses with the aim of finding a structure capable of conserving the linear state of polarization in these waveguides. It is shown that the thermoelastic stresses in waveguides of this type are fundamentally inhomogeneous, but this inhomogeneity is least when the distances between the cores and from the surface of the waveguide are the same. In a structure of this type the tangential stresses are close to zero, which is a necessary condition for linear polarization of the HE₁₁ eigenmodes.

A probe wave (λ = 1.28 μm) experienced a phase shift due to the interaction with a signal wave (λ = 1.55 μm) in a nonlinear fiber interferometer with arms differing by 5.7 km. Measurements showed that for a signal wave of 70 μW power this phase shift amounted to 5 × 10 ⁻². Such a shift measurement method should be suitable for nondestructive determination of the number of photons.

A study is made of the dynamics of solitons in fiber waveguides with slowly varying parameters. Equations are derived for the description of the evolution of soliton parameters. It is shown that in a wide range of the fiber waveguide characteristics the velocity of a soliton satisfies the Riccati equation. An estimate is obtained for the energy of the radiation generated during motion of a soliton in an inhomogeneous fiber waveguide. An analysis is made of the influence of radiation losses on the transfer of data along fiber-optic communication lines.