Torsion and conservation laws

The interaction of spinor and electromagnetic fields with the torsion of space-time is studied within the framework of the Einstein-Cartan theory. The equivalent nonlinear theory in Riemann space is obtained. The conservation laws for the vector and pseudovector currents are investigated in the nonlinear theory.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 50–52, February, 1986.     

A new variant of nonlinear electrodynamics. I

Equations are derived for a nonlinear electromagnetic field, the nonlinearity of which is produced by spin-spin coupling induced by curvature of space-time. The electrostatic solution of these equations in Minkowski space is studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 81–87, September, 1978.     

Space-time dependences of the temperature and concentration of hydrogen nuclides in the plasma-forming target of a laser source of deuterons

The space-time dependence of the temperature and concentration of hydrogen nuclides in a plasma-forming target with the composition ZrD of a laser source of deuterons is calculated taking into account the decomposition of zirconium hydride, occurring deep in the target, together with the laser evaporation of matter on the surface of the target. The results obtained enable qualitative explanation of the behavior of the deuteron emission during the operation of the ion source.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 49–53, May, 1988.     

Near-surface second-harmonic generation for autocorrelation measurements in the uv

Autocorrelation measurement of ultrashort uv laser pulses using non-phasematched second-harmonic generation from the surface of nonlinear crystals is described. The technique is demonstrated for wavelengths from 378–300 nm and pulse durations of 30 ps–300 fs.     

Nonlinear electrodynamics and anisotropic space-time

The metrical properties of four-space in the presence of a nonlinear electromagnetic field in vacuum are investigated. It is shown that the metric induced by the nonlinear electromagnetic field has a complicated nature and corresponds to an anisotropic space-time, i.e., to a four-space in which birefringence is observed. A special case of such a space is ordinary Riemann-Euclid space. As an example, the influence on the metric of the radiative corrections that follow from quantum electrodynamics is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 52–55, April, 1980.     

A new variant of nonlinear electrodynamics. II

The electrostatic solution of nonlinear electrodynamic equations is studied, the characteristic peculiarity of these equations being their consideration of the effect of electromagnetic spin on the space-time continuum. The energy of the nonlinear electromagnetic field proves to be finite for a quite wide spectrum of seed masses. Three-dimensional soliton solutions are constructed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 46–53, October, 1978.We express our deep indebtedness to N. N. Kolesnikov, V. R. Khalilov, and participants in the theoretical physics seminar led by Professor D. D. Ivanenko for evaluating the results of the study.     

Laser-optical path to nuclear energy without radioactivity: Fusion of hydrogen–boron by nonlinear force driven plasma blocks

Anomalous interaction of terawatt-picosecond laser pulses allows side-on ignition of solid state density fusion fuel with the unexpected possibility of igniting uncompressed hydrogen–boron p-¹¹B. Suppression of relativistic self-focusing by using very clean laser pulses with an extremely high contrast ratio is essential to achieve ignition thresholds only ten times more difficult than fusion of deuterium–tritium (DT). This opens the possibility for laser driven fusion energy without neutrons and less radioactivity than from burning coal. The complex nonlinear optical properties involved are elaborated.     

Harmonic and sum-frequency generation of pulsed laser radiation in BBO,LBO, and KD*P

The optical properties of the nonlinear crystals lithium borate (LBO), barium borate (BBO) and deuterated potassium phosphate (KD*P) are compared for second and third harmonic generation of Nd:YAG laser radiation. In an experimental investigation the conversion efficiency has been measured as a function of the energy density of 8 ns long laser pulses, generated by a commercial Nd:YAG oscillator-amplifier system. In LBO and BBO the second harmonic generation saturates at an energy density of about 1.5 J cm^–2 at efficiencies of 55–60%. In KD*P comparable efficiencies (40–55%) require energy densities of 2–2.6 J cm^–2. Similar results are obtained for frequency tripling. In LBO and BBO saturated efficiencies of 20–25% are measured at an energy density of about 1.5 J cm^–2. In KD*P efficiencies of 20% are obtained at energy densities exceeding 2 J cm^–2. Besides for doubling and tripling of Nd:YAG laser radiation the phase-matching is calculated for frequency conversion of tunable laser light. The results demonstrate that in LBO and BBO phase-matched sum-frequency mixing of UV and infrared laser light generates tunable radiation at wavelengths as short as the transmission cut-off at 160 nm and 190 nm, respectively.     

Nonlinear power attenuation of the radiation of a pulsed CO2 laser in the atmosphere near the ground

Conclusion Thus, as a result of the natural investigations performed on the propagation of short (microsecond) pulses of CO₂ laser radiation in the near-ground atmosphere, quantitative data are obtained on the nonlinear power attenuation of powerful radiation by the atmosphere in the range of energy densities w = 3–18 J/cm² as a function of the meteorological conditions and the turbulent state of the atmosphere. It has been shown that the principal mechanism of nonlinearity of the medium along a 100–250 m path is the origin of low-threshold optical breakdown centers on solid aerosol particles. The initiation conditions and the main characteristics of an extended laser flash in the atmosphere have been investigated.Future work of interest is to obtain statistically justified dependences of the nonlinear power attenuation and distortions of the structure of beams of powerful pulsed radiation along extended paths on the basic opticometeorological parameters of the state of the atmosphere.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 5–13, February, 1983.     

Light Squeezing in a Fabry–Perot Cavity

A quantum mechanical model for the study of quadrature squeezing in radiation coming out of Fabry–Perot cavity containing nonlinear Kerr medium has been proposed. We have incorporated the vacuum fluctuations entering in the cavity through unused ports. The analysis has been applied to a sample of GaAs filled in the Fabry–Perot cavity and irradiated by an off-resonant Co:MgF₂ laser. Limitations on achievable squeezing due to incident pump power, interaction time, nonlinear coupling parameter and facet reflectivities have been discussed and it is seen that low reflectivity of front facet and high reflectivity of rear facet of the cavity produces substantial squeezing.     

Dynamics of a Loss-Modulated, Two-Wave CO2 Laser Lasing on Lines of Different Vibrational Bands

The nonlinear dynamics of a loss-modulated, two-wave CO₂ laser lasing on vibrational–rotational lines of different vibrational bands has been investigated theoretically and experimentally. It is shown that the time and energy parameters of laser radiation can be controlled within fairly wide limits by changing the depth and frequency of modulation and the ratio between the constant components of the losses.     

Generation of picosecond pulses in solid-state lasers using new active media

Results are reported of investigations aimed at generating nanosecond radiation pulses in solid-state lasers using new active media having broad gain lines. Passive mode locking is accomplished for the first time in a BeLa:Nd³⁺ laser at a wavelength 1.354 m, and in a YAG:Nd³⁺ laser on a 1.32–m transition. The free lasing and mode-locking regimes were investigated in an alexandrite (BeAl²O₄:Cr³⁺) laser in the 0.72–0.78–m range and in a synchronously pumped laser on F 2- centers in LiF in the 1.12–1.24–m region. The features of nonlinear perception of IR radiation by the eye, using a developed picosecond laser on F₂ ^– centers, are investigated for the first time.Translated from Lazernye Sistemy, pp. 67–86, 1982.     

Intra-cavity spectroscopy with diode lasers

A multi-mode diode laser with an external cavity is studied experimentally and theoretically for its application to intra-cavity spectroscopy. One facet of a typical Ga_0.89Al_0.11As laser diode was antireflection-coated by deposition of HfO₂ such that 10^–3 residual reflectivity was left over. This diode was placed in an external optical cavity. The emission spectrum of this diode laser is highly sensitive to any frequency-dependent loss in the cavity, and the detectivity of such a loss grows with the pump rate. Even close to threshold, the absorption at 780 nm of Rb atoms with a density of 5×10¹⁰ cm^–3 has been detected. An adequate model for diode lasers based on rate equations and including frequency-dependent gain saturation is developed and applied to the calculations of output spectra. The sensitivity of these spectra to intra-cavity absorption is determined by the overall cavity loss — which is rather high — and the fraction of spontaneous emission in the total emission, in contrast with dye lasers where it is limited by nonlinear mode coupling. Various criteria for the sensitivity are suggested. The smallest detectable absorption with a perfectly antireflection-coated laser is 10^–6 cm^–1. Improvement of the characteristics of the laser diode would increase the sensitivity.     

A Kinetic Theory Approach to Quantum Gravity

We describe a kinetic theory approach to quantum gravity by which we mean a theory of the microscopic structure of space-time, not a theory obtained by quantizing general relativity. A figurative conception of this program is like building a ladder with two knotty poles: quantum matter field on the right and space-time on the left. Each rung connecting the corresponding knots represents a distinct level of structure. The lowest rung is hydrodynamics and general relativity; the next rung is semiclassical gravity, with the expectation value of quantum fields acting as source in the semiclassical Einstein equation. We recall how ideas from the statistical mechanics of interacting quantum fields helped us identify the existence of noise in the matter field and its effect on metric fluctuations, leading to the establishment of the third rung: stochastic gravity, described by the Einstein–Langevin equation. Our pathway from stochastic to quantum gravity is via the correlation hierarchy of noise and induced metric fluctuations. Three essential tasks beckon: (1) deduce the correlations of metric fluctuations from correlation noise in the matter field; (2) reconstituting quantum coherence—this is the reverse of decoherence—from these correlation functions; and (3) use the Boltzmann–Langevin equations to identify distinct collective variables depicting recognizable metastable structures in the kinetic and hydrodynamic regimes of quantum matter fields and how they demand of their corresponding space-time counterparts. This will give us a hierarchy of generalized stochastic equations—call them the Boltzmann–Einstein hierarchy of quantum gravity—for each level of space-time structure, from the the macroscopic (general relativity) through the mesoscopic (stochastic gravity) to the microscopic (quantum gravity).     

Second-order doppler-free spectroscopy

The observation of second-order Doppler-free optical resonances with a width of 50 Hz are reported for the first time. It was achieved due to the use of optical selection of cold particles from an absorbing gas. The experiments have been carried out by using a new laser spectrometer, supposed to obtain the saturated absorption resonances with a relative width 10^–13–10^–14. The results of experimental and theoretical studies of second-order Doppler-free effect influence on the shape of nonlinear optical resonances in transit-time conditions are considered.     

Ultrafast nonlinear absorption and reflection of ZnS/ZnSe periodic nanostructures

ZnS/ZnSe heterostructures under condition of ZnSe interband excitation by a 150 fs laser pulse exhibit strong narrow-band modification of absorption and wide-band modification of reflection. Mean decay time for nonlinear reflection in heterostructures ranges from 2 to 3 ps whereas in bare ZnSe monolayer it exceeds 5 ps. Possible physical processes responsible for nonlinear refraction in the transparency region include interplay of absorption driven nonlinear refraction via Kramers–Kronig relations and intrinsic dielectric properties of dense electron–hole plasma. For nonlinear absorption at ZnSe band edge, interplay of plasma screening effects and states filling effects are relevant.     

Compensation,nonlinearity, and geometry

A new approach to the theory of compensating fields is given. The theory is extended to the case of an arbitrary Lie group and leads to a nonlinear field theory, describing the interaction of physical fields and the generation by this interaction of a non-Euclidean space-time geometry, generalizing the well-known result of the Einstein theory on the connection between geometry and matter. The theory is applied to a number of groups.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 128–134, December, 1974.The author is grateful to Professor D. D. Ivanenko, who has made such significant contributions to the development of the theory of compensation and its nonlinear generalizations and to the treatment of gravitation as a gauge field. The author also wishes to thank B. N. Frolov and V. N. Ponomarev for valuable discussions.     

Strong-interaction approximation in the theory of second harmonic generation of intense short laser pulses

The method of strong interaction of nonlinear waves has been developed to analyse the second harmonic generation of intense laser radiation in the transient regime. Analytic solution for frequency conversion efficiency – taking into account the pump radiation depletion, influence of phase mismatch, dispersion of group velocities and higher nonlinearities – has been first obtained. A comparison of theoretically derived results and known experimental data has been conducted, and a general agreement of these results has been obtained. The optimal conditions of the second harmonic generation of neodymium laser radiation into femtosecond pulse duration range have been determined.     

Control of laser pulse parameters in a cavity with a thermal-nonlinearity shutter

The light pulse generation by a laser controlled by shutter from a finite-thickness absorbing layer with thermal nonlinearity has been studied theoretically. The layer placed in the cavity is oriented with respect to the mirror so that conditions for nonlinear total internal reflection of generated radiation are created. In the plane-wave approximation, a self-consistent system of nonlinear truncated equations for the field amplitudes together with constitutive equations has been obtained. Numerical simulation with the use of the obtained system has shown that it is possible to control the form and duration of the generated pulse by varying the absorption coefficient of the nonlinear medium and the angle of incidence on the absorbing layer, as well as the layer thickness.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 771–777, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Multiphoton detectors of laser radiation

The paper is devoted to the problem of using multiphoton detectors to measure the statistical characteristics of multifrequency laser radiation affecting the nonlinear interaction between radiation and matter. Section 1 gives the characteristics of laser radiation determining the probability of power-type nonlinear interaction with a medium. Section 2 briefly characterizes multiphoton detectors. Sections 3–6 are devoted to the problems of measuring the so-called statistical radiation factor by means of multiphoton detectors and to the analysis of the corresponding experimental data. The possibility of using multiphoton detectors to measure other radiation characteristics is discussed in Sections 7 and 8.Based on material presented at the first All-Union Conference on the Problems of Laser Radiation Parameter Control, Tashkent, 1978.