卷 37, 编号 5 (2016)

This article is an overview of the life and work of the outstanding Russian physicist P. N. Lebedev.

We consider the Husimi Q(q, p)-functions which are quantum quasiprobability distributions on the phase space. It is known that, under a scaling transform (q; p) → (⋋q; ⋋p), the Husimi function of any physical state is converted into a function which is also the Husimi function of some physical state. More precisely, it has been proved that, if Q(q, p) is the Husimi function, the function ⋋²Q(⋋q; ⋋p) is also the Husimi function. We call a state with the Husimi function ⋋²Q(⋋q; ⋋p) the stretched state and investigate the properties of the stretched Fock states. These states can be obtained as a result of applying the scaling transform to the Fock states of the harmonic oscillator. The harmonic-oscillator Fock states are pure states, but the stretched Fock states are mixed states. We find the density matrices of stretched Fock states in an explicit form. Their structure can be described with the help of negative binomial distributions. We present the graphs of distributions of negative binomial coefficients for different stretched Fock states and show the von Neumann entropy of the simplest stretched Fock state.

We consider general principles of spectral compression of parabolic pulses in nonlinear optical fibers. It is known that the variance analysis provides a way to describe correctly the evolution of the pulse parameters under the spectral compression. We propose a computational model of multistage amplifier with spectral compression segments incorporated. The model provides the possibility to amplify middle-power input pulses to obtain pulse energies of hundreds of nanojoules with such output spectral characteristics that provide the possibility for further effective enhancement. We also discuss a modification of the model that provides the formation of a parabolic envelope and linear frequency modulation of the output pulse.

We demonstrate an efficient method of mid-IR femtosecond-laser-pulse self-compression in transparent dielectrics based on a suitable selection of the parameters of the medium and laser radiation. We discuss the principle of selection of the nonlinear medium for ultrashort-pulse self-compression. We show that the proposed combination of the Kerr nonlinearity and negative group-velocity dispersion in a set of transparent dielectric crystals (CaF₂, BaF₂, YAG, etc.) provides a compression of the incident laser pulse to a 1–2 cycle pulse width.

Within the framework of the non-perturbative light–atom interaction theory, we consider the population dynamics of the ground-state sublevels corresponding to the different values of the orbital quantum number (l) projections and its influence on the high optical harmonics. We study the problem of high optical harmonics generation in two geometries: (1) two linearly polarized fields at frequencies ω and 2ω for different angles of azimuthal projection difference and arbitrary orientation with respect to the angular momentum of the atom direction; (2) two elliptically polarized fields at frequencies ω and 2ω rotating in opposite directions with variable mutual ellipticity. We show that the unequal population dynamics of the levels with different projections of the atom angular momentum (magnetic quantum number) has a significant impact on the value of the ellipticity of the generated radiation.

We perform the spectral analysis of fresh leaves using light-induced mid-IR emission spectroscopy (LIMIRES), a technique utilizing CW optical pumping for preparing and monitoring vibrationally excited states of chromophores. We show how to obtain high-quality IR-emission spectra of intact leaves using visible light of low intensity and sensitive Fourier transform infrared spectroscopy (FTIR). Changing the conditions of illumination, we carry out the spectral discrimination between leaf samples of wild plants and transgenic tobacco plants. Our results show that LIMIRES is a valuable new technique for studying the vibrational structure of excited pigments as well as the nondestructive monitoring of the quality of tobacco leaves.

We present an option of the experiment with a correlated pair of particles in the entangled state, which provides the effect of a change in the polarization for entangled photons, and demonstrate the reality of all different superposition states and the corresponding vector of the quantum system state; also we analyze possible consequences of this fact. We propose a quantum realism paradigm within the relational paradigm instead of the local realism concept disproved by the experiments on verifying the Bell inequalities. We analyze the results of experimental research of the Leggett inequality violation with respect to the verification of the adequacy of different kinds of nonlocal hidden variable theories and suggest a new way of their evaluation based on the study of the photon cross-correlation suppression after a beam splitter and preparation of quantum squeezed states. We show that the interpretation based on the nonlocal hidden variable theory is inconsistent.