Table of contents

A report is given of a theoretical and experimental study of the problem of vehicle propulsion in the earth's atmosphere under the action of shock waves produced as a result of CO₂-laser-induced optical breakdown of air. It is shown that there are certain optimal conditions for the transfer of pressure impulses to receivers. Conical and parabolic receivers are used as an example to show that there are maximum values of the specific impulse (also known as the coupling coefficient). The experimentally obtained specific impulse values ∼500 μN·sec·J^–1 are close to the maximum values deduced from the point explosion theory. Realization of motion of a parabolic reflector in a glass tube is reported for a pulse-periodic regime of laser emission with an average power of ∼25W. The thrust obtained is reported.

Two experiments of fundamental interest utilizing photon counting techniques are discussed. The first, not carried out as yet, aims to demonstrate an unusual phenomenon known as photon antibunching. Particular consideration is given to the experimental realization of the specific essentially nonclassical states of the electromagnetic field in which antibunching is observed. The second experiment, already carried out successfully, is concerned with the old quantum mechanical problem of the existence of hidden variables. This provides a very sensitive test of the fundamental quantum-mechanical concepts, and the results clearly confirm the quantum-mechanical prediction, and rule out any theories of local hidden variables.

Analytic and numerical solutions of the Maxwell–Bloch equations, including transverse and timedependent phase variations, predict on-resonance self-focusing (SF) and elucidate its formation due to the combined effect of diffraction and inertial response of the medium. This new SF can be characterized by a simple parameter in terms of the beam and medium parameters. Recently, two independent experiments on SF in Na and Ne demonstrated convincingly this new SF effect for spatially nonuniform self-induced transparency pulses propagating in thick resonant absorbers.

A review is given of methods of obtaining optical and ultrasonic holographic images for the study of biological objects and for medical diagnostics. A technique is described for the production of a codedaperture x-ray image with Fresnel zone plates using a solid-state image intensifier. An in-line holographic system is used as the basis for the development of a holographic ametropia tester to determine visual acuity. Shadow holograms of trembling fingers have been obtained. A holographic method is described for the determination of the three-dimensional distribution of a malignant tumor. Ultrasonic holographic techniques are utilized to study tissue characteristics. A holographic Fourier spectrometer is being developed to investigate backscattering of radiation by the retina. Examples of bioholographic models of information processes are given.

Solutions are obtained describing cw and pulse-periodic lasing regimes in a CO₂ laser with high mean output power. In the pulse-periodic regime the mean power and the repetition frequency are at present limited to 450 W and 33 Hz in a 40×10×10 cm discharge. The laser properties are all described accurately by theoretical expressions obtained on the basis of a four-temperature model. The use of this model, together with the gasdynamic equations, provides a reliable method of predicting the operation of a supersonic-flow laser in the cw regime.

A description is given of a copper vapor laser in whose capillary two successive discharges are produced, one serving to form the vapor and the other to create a population inversion in it. Since the capillary temperature is practically independent of the parameters of the gas discharge producing the inversion, it is easier to optimize the discharge circuit parameters.

A theoretical analysis is made of the possibility of constructing a cw singly resonant optical parametric oscillator. A numerical solution is given of the problem of optimal focusing of pump radiation with the aim of minimization of the lasing threshold. The calculations are carried out for spherical and hemispherical resonators making allowance for the birefringence of the nonlinear crystal.

An analysis is made of the possibility of observing an anticorrelation effect in optical parametric processes (both degenerate and nondegenerate) with classical and quantum pumping. It is shown that the time dependence of the photon statistics in the anticorrelation regime reduces the indeterminacy (quantum noise) to a level below that in the coherent state case.

A description is given of a spectrometer for recording coherent anti-Stokes Raman-scattered signals. The results are reported of an investigation of the v₁ (1525 cm^–1) band of β-carotene, carried out using this spectrometer.

It is shown that quasiresonant pumping at the frequencies of lines used in coherent anti-Stokes Raman spectroscopy (CARS) causes a change in the ratio of the absorption and emission intensities because of reversal of the sign of the real part of the Raman scattering susceptibility. The changes in the line profile with the concentration of a substance subjected to long-wavelength pumping are due to reversal of the sign of the imaginary part of the susceptibility. An expression is obtained for the dependence of the CARS line profile on the pump intensity.

A comparison is made of inverse Raman scattering (IRS) and coherent anti-Stokes Raman scattering (CARS) from the point of view of their applicability in Raman-spectroscopic investigations of liquid media. Important aspects in this context are the detection limit of weak Raman lines, the comparability of their profiles with those of spontaneous Raman scattering (SPRS) lines, and the feasibility of utilizing the resonant Raman effect. Both methods were implemented using experimental setups with two pulsed lasers (narrow- and broad-band).

An experimental and theoretical investigation was made of the interference of excited electronic states in continuum resonance Raman scattering in bromine.

The first experimental and theoretical investigations of the Raman-induced Kerr effect (RIKE) in crystals are reported. A Stokes continuum in the 725–740 nm range was used to record the A(LO) vibration at 817 cm^–1 in the RIKE spectrum of an LiIO₃ crystal. Allowance was made for the appearance of a polariton field and possible manifestation of the optical activity in the description of the steady-state effect by means of general RIKE equations for noncentrosymmetric uniaxial crystals. Moreover, a transient probe-beam method for the determination of the time T₂ was considered and it was compared with analogous coherent anti-Stokes Raman scattering methods.

A review is given of experimental and theoretical achievements in studies of multiphoton spontaneous scattering processes in atomic and molecular media. An analysis is made of integral multiphoton scattering, particularly of scattering in statistically inhomogeneous media with short-range quasiorder. A study of the intensity of the noncoherent multiphoton scattering component provides direct information on the nonlinear polarizability of atoms and molecules whilst the coherent component is associated with various atomic and molecular correlation mechanisms. An analysis of the spectra of elastic and inelastic multiphoton scattering processes yields information on the translational and rotational motion of the molecules. In particular, it is possible to measure the higher-order rotational relaxation times and to verify the adequacy of the various stochastic models of molecular motion. Observations of the spectral lines of three- or more-photon scattering, which obeys new selection rules, yield detail on the fine structure of the molecules and their linear and nonlinear vibrations. Examples are given of the most interesting spectra of three- or more-photon scattering in gases, liquids, and crystals obtained in singleand multichannel systems. The stochastic theory of multiphoton scattering in liquids is discussed, using the spherical tensor concept. The derived general expression reduces to known results for certain cases.

The interaction of light waves in crystals with a quadratic nonlinearity is considered. It is shown that when one of the interacting waves carries information on the image of an object, such information can be transferred to a different wavelength, providing the basis for a parametric image converter. The results are given of experimental measurements of the noise and sensitivity of parametric-conversion detectors. It is shown that when both interacting waves carry information on an object, the interaction in a nonlinear crystal allows us to obtain correlation functions of the initial images of the objects. Suitable systems make it possible to determine experimentally the correlation function of the images of simple objects. By way of example, a description is given of a system which makes it possible to remove phase distortions introduced by an optical system in the far-field zone.

A study is made of the efficiency of two-photon absorption of a two-mode laser field with phase diffusion. Numerical computer calculations are reported.

A semiconductor injection laser operating in the pulsed regime at room temperature was used as part of a composite resonator system. A diffraction grating formed one of the resonator mirrors which permitted the radiation spectrum to be tuned over a wide wavelength range. A study was made of the competition between the laser modes and the resonator emission lines.

An investigation of the interaction between a laser beam and glass produced typical damage effects in different parts of a specimen; in one part the cutting action was due to the material being removed and in the other it was due to thermomechanical action. Cutting regimes were determined for particular cases.

An investigation was made of the possibility of using argon laser radiation in surgery. Measurements were made of the rate of cutting (burning) of mucous membrane, bone, and muscle tissue as a function of the radiation power density. Moreover, the temperature distribution near the operation zone was determined. The results of clinical tests of treatment of vasomotor nasal diseases are given.

A description is given of a spectrometer for linear absorption measurements in the infrared. An optical parametric oscillator (OPO) based on a LiNbO₃ crystal pumped by the second harmonic of a neodymiumdoped garnet laser was used as a tunable source of coherent radiation. Using this OPO, a resolution of 10⁵ was achieved.

A report is given of the experimental results obtained using a CO₂-laser saturation spectrometer with an external absorption cell, mounted between two polarizers, the saturating and probing beams having different polarizations. The molecules SF₆, NH₃, CF₂Cl₂, and BCl₃ were investigated and the nonlinear resonance corresponding to transitions with Δ J=0,±1 was observed.

A description is given of a high-resolution spectrometer which uses a dye laser, stabilized relative to a reference cavity by means of a multistage system with two He—Ne lasers, one free-running and the other Lamb-dip-stabilized. This spectrometer was used to measure the isotopic shifts of the naturally occurring isotopes of krypton and of radioactive ⁸⁵Kr and ²²Na (relative to ²³Na).

A method of separating iodine isotopes is proposed. This method is based on the large difference between the rate constants of the reactions of the excited I (²P_1/2)and unexcited I (²P_3/2) iodine atoms with CF₃ radicals and Cl₂ molecules and on the feasibility of selective irradiation of ¹²⁷I atoms in the ²P_1/2 and ²P_3/2 states by a photodissociation iodine laser utilizing R¹²⁷I molecules (λ =1.315 μ). A method of separating the pure isotope ¹²⁹I from a mixture of ¹²⁷I and ¹²⁹I is discussed.

An investigation is made of the influence of the finite correlation time of dissipative processes in a liquid solution on nonlinear resonance phenomena. Typical ranges of frequencies of relaxation processes are given. Allowance for the finite relaxation time is made in a calculation of the gain of stimulated resonance Raman scattering of the first and second types excited by quasiresonant pumping. The conditions under whiph stimulated resonance Raman scattering can be observed are considered.

A new excitation method is proposed for shaping and lengthening the output pulse of TEA CO₂ lasers, based on the independent excitation of two or more coaxial discharge systems contained in the same resonator. The shape of the TEA CO₂ laser pulse is derived, from the rate equations, as a function of the delay time between the two discharge-current pulses. The first experimental results for a laser of this type are presented.

The results are given of an experimental estimate of the quality of an image at the output of fiber laser amplifiers of transmission and reflection types. It is shown that the active regime of operation of a fiber bundle makes it possible to increase considerably the absolute value of the image contrast, compared with the passive regime. The resolution of a reflection-type fiber laser amplifier approaches the limit governed only by the diameters of the component fibers and is independent of the regularity of fiber packing in a bundle.

The spectra of a cw YAG:Nd laser were investigated using a Fabry–Perot interferometer. The laser was mode-locked by an acousto-optic modulator. A band width of up to 4.8 GHz was obtained, corresponding to a pulse length of 200 psec.

A report is given of the development and of tests on a Q switch for continuously pumped YAG:Nd lasers. The switch operates in the Raman-Nath diffraction range. The results are given of a study of the propagation of acoustic waves in such a switch, and also of the acoustic and electrical matching of all the parts of the switch. It is shown that the presence of a reflected acoustic wave in an optical medium is an undesirable effect.

A report is given of measurements of the fluorescence lifetimes of neodymium ultraphosphate NdUP (NdP₅O₁₄) single crystals. The dependence of the measured lifetimes on the number of excited molecules is given. According to the proposed mechanism, the reduction in the lifetime is due to intermolecular interactions in this highly concentrated material.

An experimental investigation was made of the structural surface and bulk defects, revealed by x-ray topographic and optical microscopic analyses, on the damage threshold and crater morphology of KDP crystals.