Table of contents

An experimental investigation was made of the dispersion of the phase response (i.e., of the frequency dependence of the change in the refractive index caused by illumination with strong light) of solutions of rhodamine 6G and 3,3-diethyloxadicarbocyanine iodide (DODCI) in the spectral range covering the absorption and fluorescence bands. The qualitative nature of the dispersion of the phase response was the same for both dyes and it was in good agreement with the expected behavior.

A study was made of the mechanism and products of ablation of atherosclerotic plaques and arterial walls by laser radiation of wavelengths 308, 539, and 1078 nm at energy densities 0.5–8 J/cm². Visible and infrared radiation were found to have a tissue damage threshold of 3–4 J/cm² and the process was "explosive" involving ejection of large fragments. Ultraviolet radiation resulted in "soft" ablation of tissues throughout the investigated range of energy densities with the minimal effects on the underlying layers. The specific energy of ablation in air was  1.1 ±  0.3 kJ/g and the effective quantum yield of volatile products in vacuum was   0.8 ± 0.3. The quantum yield of lipids and their photoproducts was approximately the same at all the wavelengths and did not exceed 10⁻³. The results obtained confirmed the photochemical mechanism of ablation of tissues by XeCl laser radiation.

Emission of 585.3 nm pulses of 1.5 k W power (∼ 15 kW/liter) was observed from a mixture of the Ne:H₂ = 2:1 composition at p = 0.65 atm and a record-low input energy ( ≲ 30mJ). The excitation source was an electron beam from a MIRA-2D industrial x-ray unit.

A theoretical analysis is made of the possibility of shortening picosecond infrared radiation pulses by propagation in semiconductors. The shortening is due to a change in the density of free carriers as a result of interband absorption of the propagating pulses.

A review is presented of the literature on the selective effect of optical radiation on cancer cells sensitized with porphyrin dyes. Particular attention is paid to an explanation of the fundamental principles of photodynamic cancer therapy and the physical mechanisms of the accompanying processes. The results are presented of the first applications of photodynamic therapy in the treatment of oncological diseases and the laser requirements are formulated. The use of fluorescence spectroscopy for cancer diagnostics is considered. Modern laser spectroscopic techniques used to study individual cells and cell cultures are discussed: laser picosecond fluorescence microscopy and Raman light scattering spectroscopy.

An experimental investigation was made of the time profile of Stokes pulses as a function of the energy, repetition frequency, and conditions of focusing of laser pulses in various systems of stimulated Brillouin scattering (STBS) mirrors. Cascade STBS shortening of laser pulses reduced the duration from 12 nsec to less than 0.2 nsec in the case of Stokes pulses.

The method of double-exposure holographic interferometry was used to investigate the gasdynamic collapse of a laser plasma initiated by a gigawatt CO₂ laser pulse. The laser beam was tubular and it was focused onto a carbon target. The holographic method enabled the parameters of the laser plasma to be measured with a spatial resolution of better than 25 μ. The spatial distribution of the electron density during the laser pulse interaction was determined. Estimates were obtained of the axial and radial velocities of the erosion laser plasma and an analysis was made of the relationship of these parameters to the experimentally determined shock wave velocity in the residual gas. It is proposed to use the laser plasma formed during a gasdynamic collapse as the active medium of short-wavelength lasers.

An integrated structure was made containing a laser and a photodetector, with a high transmission coefficient of the optical power, in a monolithic module utilizing an AlGaAs/GaAs heterostructure forming a system of coupled waveguides. Efficient operation of the laser having a broad contact was achieved by the presence, within its active part of regions of alternating length. Variation of the lengths of the elements of a line of slots with vertical walls, used as a resonator mirror, made it possible to vary the coefficient of coupling between the laser and the photodetector from practically 0 to 100%.

A theoretical model is developed of an atomizer-type generator of O₂(¹Δ) intended for an O₂(¹Δ)–I laser. Various operating regimes of this generator are considered. It is shown that a high O₂(¹Δ) productivity can be achieved simultaneously with a high degree of excitation of the oxygen. A study is made of the operating regimes of the generator which can ensure high O₂(¹Δ) densities up to 100 kPa. Other advantages of such a generator are also considered.

A calculation is made of the correlation function and of the energy spectrum of the signal from a single-beam heterodyne laser Doppler anemometer under conditions of partial spatial coherence of the probe beam. This partial coherence is an unavoidable factor, for example in studies of the flow in blood-carrying capillaries and living cells. The results are reported of an experiment in which the Doppler spectra were recorded for water carrying particles of polystyrene latex in a planar glass channel 200μ thick. The coherence of the probe beam was degraded by phase screens placed in front of the channel. It was found that broadening of the spectra was governed by the transit time of particles crossing a region of the order of the correlation radius of the radiation field in the measurement zone.

A stochastic distributed feedback mechanism is proposed to account for the experimental results (blue shift of the wavelength, reduction of the threshold) on the lasing of a dye in a liquid crystal matrix. It is shown that this mechanism involves scattering by inhomogeneous fluctuations of the order and provides a correct quantitative description of the experimental data.

An analysis is made of the influence of variation of the detuning of the frequency of a resonator mode from that of an external injected signal on the operation of pulsed gas lasers. It is found when the detuning is varied with time there is an increase in the width of the locking region of a resonator mode in pulsed lasers. The results are given of numerical calculations of the dependences of the locking efficiency on the parameters on the injected signal and of the laser active medium.

Image of amplification by a factor of ∼ 10⁵ and an increase in the contrast by a factor of 10³ were achieved by intracavity image readout from spatial light modulators. Two types of photosemiconductor–liquid crystal modulators were used: 1) utilizing a cholesteric–nematic phase transition; 2) utilizing the electrooptic effect in a nematic liquid crystal. The image quality was at the diffraction limit both for a dye laser and a YAG:Nd³⁺ laser; the sharpness of the image boundaries and the contrast increased above the lasing threshold. When readout took place from an area of the diffraction-limit size in a free-running YAG:Nd³⁺ laser, the radiation energy was 0.8 × 10⁻³ J and the energy density reaching the modulator was ∼ 1.4 J/cm² (the energy of the recording light of the λ = 0.44 μ wavelength was ∼0.4 × 10⁻⁸ J and the energy density in the recording stage was ∼10⁻⁶J/cm²).

An investigation was made of the scattering of radiation from a single-frequency neodymium laser when optical breakdown took place in transparent dielectrics and gases. A scattering peak with a preferential forward direction was observed in ∼ 100 psec from the breakdown. This peak was due to the reflection by the boundary of a plasma cloud which always appeared at the center of the caustic of the focusing objective. It was demonstrated that the main stage of the optical breakdown developed in a time of ∼ 100 psec.

Quantum–statistical properties of radiation are studied under conditions of a nonlinear interaction between electromagnetic interfering fields and a relativistic electron beam, as well as under degenerate four-wave mixing. Conditions for the occurrence of photon bunching and antibunching, and of "squeezed" states are identified.

The frequency of a dye laser locked to an I₂ peak at 576 nm is to be measured against a pair of cesium-calibrated rubidium clocks by using a harmonic-generation and frequency-mixing chain and counting the beats simultaneously. Much of the chain has been constructed and a color-center laser required is being developed. A pair of I₂-stabilized dye lasers have been found to have a single-sigma reproducibility of about 19 kHz or 4 parts in 10¹¹.

Over three hundred new submillimeter emission lines were predicted for the ν₅ band of deuterated fluoroform CDF₃ pumped by isotopic CO₂ and N₂O infrared lasers. These lines were calculated by using recently derived molecular constants determined by fitting known infrared, microwave, and submillimeter transitions in CDF₃. The calculated emission lines (estimated accuracy generally within  ± 1 MHz) should be useful to those with specific wavelength requirements. The CDF₃ molecule provides a rich choice of frequencies at approximately 20-GHz intervals extending from about 40 GHz to beyond 1 THz.

Coherent anti-Stokes Raman scattering (CARS) is well adapted to the measurement of temperatures and concentrations of molecules in reactive gaseous media. The general principles are given along with the major technical advantages and requirements. Characteristic applications are described in order to present state-of-the-art performance levels: measurement time, spatial resolution, detection sensitivity. Results are presented of instantaneous temperature measurements in combustion and in piston engines, measurements of rotational–vibrational populations of H₂ in a magnetic multicusp discharge, and measurements of the vibrational excitation of the prompt H₂ formed in H₂CO dissociation.

A description is given of an optoacoustic method for nonintrusive measurement of the energy of light pulses and for monitoring the mirror surface quality by recording the amplitude of displacement of the rear side of a mirror reflecting laser radiation. A theory of the method is given. Experimental tests of this theory are reported for mirrors made of three different materials. The method is particularly valuable in the case of high-power laser systems and for monitoring the surface quality of mirrors with high reflection coefficients.

An analytical and numerical investigation is made of "steady-state" optical breakdown in rare gases near refractory metals irradiated with a cw CO₂ laser. Surface temperatures are considered at which there is no ionization equilibrium in the mixture of the gas and the metal vapor, and the electron distribution departs from Maxwellian (for tungsten, 3.5 ≤ T_m < 4.5 kK). In the proposed model of optical breakdown we shall take into account both direct ionization and multistage ionization involving the excitation of the metastable levels in the gas and in the metal vapor. An analytical breakdown condition is deduced for the case when the system has a plane geometry. The threshold power density is found to depend on the heat of vaporization of a metal ion from the surface. The optical breakdown threshold in argon near a tungsten target is calculated numerically for a cone of radiation.

An analysis is made of the emission of H and E waves in the first diffraction order from a diffused waveguide where the permittivity is harmonically modulated along the waveguide and the transverse distribution is arbitrary (for an arbitrary angle of incidence of surface waves on a volume grating). It is shown that if the relative transverse distributions of the permittivity increment in the waveguide layer and its modulation amplitude are the same, the coefficients of diffraction attenuation of the surface waves can be expressed in a closed analytic form in terms of the parameters of a weak diffused periodic waveguide.

An investigation is made of the behavior of the variance and of the spatial correlation coefficient of the intensity of optical radiation reflected by a turbulent atmosphere as a function of the position of the plane of observation relative to the entrance pupil of the front lens of a telescope. It is shown that enhancement or attentuation of intensity fluctuations in the image plane of the lens, compared with the fluctuations in the plane of the lens itself, is localized in a region which is limited in the longitudinal direction. These effects and the dimensions of the localization region depend on the parameters of the receiving system and the initial coherence of the source field.

An investigation is made of the influence of the choice of possible mechanisms for filling of the levels and the choice of various expressions for the rates of the elementary processes on the distribution of Al ions over excited levels and ionization states. The calculations are made using the collisional radiative model (steady-state case) in the approximation of an optically thin plasma. It is shown that the neglect of impact deexcitation and three-particle recombination processes results in overpopulation of the first excited level and distortion of the Boltzmann distribution in highly excited levels.

The third harmonic of a mode-locked YAG:Nd³⁺ (λ = 355 nm) solid-state laser was generated for the first time. A crystal of LiIO₃ was found to be promising for the generation of near-ultraviolet radiation in the cw and quasi-cw regimes. An average ultraviolet radiation power of 4.5 mW was obtained in the mode-locking regime.

A study was made of the optical breakdown threshold of the surface of K8 glass subjected to low-temperature ion-exchange diffusion in KNO₃ and NaNO₃ melts. It was found that the treatment of glass in KNO₃ increased and that in NaNO₃ reduced the breakdown threshold. The increase in the threshold was due to removal of absorbing inclusions in the process of diffusion treatment in the chemically active molten salt. Compressive stresses in the diffused layers reduced the size of the cracks in the surface layer of glass and stabilized the time dependence of the breakdown threshold.

A study was made of the propagation of strong pulsed CO₂ laser radiation along a ground atmospheric path. A mechanism is proposed to account for the anomalous attenuation of the radiation during a pulse.

Typical excitation conditions in a pulsed electron-beam-controlled CO laser were studied and the times for attaining a fixed unsaturated absorption level due to different vibrational transitions of the CO molecule were determined. These times were compared with those calculated by varying the values of the short- and long-range components of the vibrational–vibrational (VV) exchange constant. The values of these constants were then refined.

A multimode optical fiber was used as a wavefront-reversing mirror in a four-pass laser amplifier utilizing neodymium phosphate glass.

The results are reported of the development and preliminary testing of a compact industrial CO₂ laser source in which the gas is circulated with a centrifugal fan. The specific overall volume of the device is 0.6 m³/kW for a laser output power of 5 kW.

It is shown that the maximum gain of an optical quantum amplifier can be increased by a Doppler shift of the spectral emission line of the active substance.

Amplification and stimulated emission of radiation of the 10.6 μ wavelength was observed as a result of supersonic mixing of carbon dioxide with the products of air gasification of carbon.

A study was made of the influence of the technology used in the fabrication of a dielectric barrier on the luminescence spectrum of a metal–barrier–metal (MBM) diode. The barrier was formed by electron-beam sputtering or by ion implantation. Various methods of fabrication of the barrier layer affected the electrophysical characteristics, but not the spectral properties of tunnel MBM diodes. This confirmed that the plasma mechanism was the main reason for the luminescence of radiation by MBM diodes.

An investigation was made of the lasing characteristics of solutions of various new dyes in the coumarin, naphthalimide, and benzanthrone classes pumped transversely by the second harmonic of ruby laser radiation. Lasing in the blue, green, and red parts of the spectrum was obtained for most of the compounds studied. A comparison was made between these materials and laser dyes widely used in these spectral ranges. The compounds studied included some with a lasing efficiency substantially higher than uranin in the green and cresyl violet in the red, and with a photostability not inferior to these two.

An investigation was made of the influence of a light-reflecting polymer cladding (made of a fluoroplastic F-42) on the optical losses in fiber waveguides made of chalcogenide glasses belonging to the As–Se, Ge–As–Se, and Ge–As–S systems. Deposition of a light-reflecting polymer cladding on fibers 300–500μ in diameter increased the optical losses in the wavelength range 2–7μ by 0.2–0.8 dB/m and by more than 2 dB/m in the range 7–12μ.

An analysis is made of sound generation in the interaction between two orthogonally polarized components of a high-power ultrashort light pulse in an anisotropic crystal exhibiting electrostriction. It is shown that the envelope of an acoustic pulse takes the form of the autocorrelation function of the complex amplitude of the ultrashort pulse and its duration is between 6 and 7 orders of magnitude greater than that of the ultrashort pulse.

It is proposed to activate liquid-crystal matrices with 3-acyloxy derivatives of oxazine 17 which are highly soluble in such matrices and exhibit a high degree of order. The results are reported of an investigation of lasing of these dyes in isotropic and mesomorphic phases.

A determination was made of the characteristics of an electric-discharge XeCl laser with x-ray preionization and quasi-cw excitation. An electrical line with ceramic capacitors was used for the first time as a storage device. A specific laser output energy of 3.25 J/liter and an efficiency of ∼ 1.6% was achieved. Matching of the line and discharge gap impedances was found to be possible at high charging voltages by adding helium to the Ne–Xe–HCl active medium.

A determination was made of the frequency of an HeAr laser emitting the line as a result of the transition in Ar I. The measured frequency was synthesized by a metaloxidemetal diode from the fourth harmonic of the frequency of a CO laser corresponding to the (24) emission line at and the frequency of a microwave oscillator emitting in the range of 39 GHz. The synthesized frequency was MHz.

A determination was made of the attenuation in a three-fiber optical load-carrying cable fabricated under different conditions. Optimization of the twisting process made it possible to construct an optical load-carrying cable with attenuation in its three channels not exceeding that in the original optical fibers.

It is shown that consecutive interaction of three waves in several spatially separate identical nonlinear media provides an additional opportunity for the control of the nature of this interaction. Ways of using this interaction in acoustooptics and nonlinear optics are indicated.

The method of Raman-induced Kerr effect spectroscopy was used to record spectra of the band and a panoramic spectrum including O, , and S bands of atmospheric nitrogen with a resolution of 0.1 cm ⁻¹ at 293 K under normal pressure. Ways of utilizing this method for remote diagnostics of the atmosphere are considered.

Closed convective flow of the gas in discharge tubes of pulse-periodic lasers was observed for the first time. The results obtained indicate that the observed flow was similar to the Rayleigh flow in strong acoustic fields. The time-average value of the flow velocity was governed by the deposited energy (per molecule) and depended resonantly on the repetition frequency of the excitation pulses.

An analysis is made of the efficiency of heating of disperse particles moving with a gas stream parallel to a laser beam. It is shown that when fairly high-intensity (∼ 10 kW/cm²) cw CO₂ laser radiation is used, the efficiency of heating of strongly absorbing particles reaches ∼40%. This suggests that laser radiation may be used to heat particles in various technological processes.

An investigation was made of the mode composition and time characteristics of an argon laser with an intracavity electrooptic modulator tuned to the intermode beat frequency. The parameters of the intracavity interaction needed to ensure stable phase mode locking were determined. Several carriers appeared in the frequency-modulated spectrum in the case of multifrequency free running. These carriers were attributed to the presence of supermodes in the gain profile of the active medium. Amplitude modulation of the radiation at the frequency of 0.5 MHz was observed and it was explained by coherent addition of carriers in the frequency-modulated spectrum.