arXiv subjects

Oleksandr O. Chumak

Publications and source records attributed to Oleksandr O. Chumak.

4 recordsLinked to original sources

arXiv2020

Fourth-order moment of the light field in atmosphere

The quasiclassical distribution function for photon density in the phase space is obtained from solution of the kinetic equation. This equation describes propagation of paraxial laser beams in the Earth atmosphere where "collision integral" embodies the influence of turbulence. The anisotropy of photon distribution is shown and explained. For long propagation path, the explicit expression for fourth-order moment of light is obtained as a sum of linear and quadratic forms of the average distribution function. This moment describes a spatial correlation of four light waves, giving the information about the photon distribution in the cross-section of the beam. The fourth moment can be measured using two small detectors outside the central part of the beam. The linear form describes the shot noise (quantum fluctuations) of photons. The range where the shot noise exceeds the classical noise is found analytically. Derived photon fluctuations are the valuable source of information about statistical properties and local structure of the laser radiation that can be used for applications.

quant-ph↗

arXiv2018

Laser-beam scintillations for weak and moderate turbulence

The scintillation index is obtained for the practically important range of weak and moderate atmospheric turbulence. To study this challenging range, the Boltzman-Langevin kinetic equation, describing light propagation, is derived from first principles of quantum optics based on the technique of the photon distribution function (PDF) [G. P. Berman et al., Phys. Rev. A 74, 013805 (2006)]. The paraxial approximation for laser beams reduces the collision integral for the PDF to a two-dimensional operator in the momentum space. Analytical solutions for the average value of PDF as well as for its fluctuating constituent are obtained using an iterative procedure. The calculated scintillation index is considerably greater than that obtained within the Rytov approximation even at moderate turbulence strength. The relevant explanation is proposed.

quant-ph↗

arXiv2015

Correlations of photon trajectories in the problem of light scintillations

A distribution function approach is applied to describe the dynamics of the laser beam in the Earth atmosphere. Using a formal solution of the kinetic equation for the distribution function, we have developed an iterative scheme for calculation of the scintillation index ($σ^2$). The problem reduces to obtaining the photon trajectories and their correlations. Bringing together theoretical calculations and many-fold computer integrations, the value of $σ^2$ is obtained. It is shown that a considerable growth of $σ^2$ in the range of a moderate turbulence is due to the correlations of different trajectories. The criteria of applicability of our approach for both the coherent and partially coherent light are derived.

quant-ph↗

arXiv2014

Photon distribution function for propagation of two-photon pulses in waveguide-qubit systems

Propagation of a two-photon pulse in a waveguide coupled to a two-level system (TLS) is studied. The pulse is formed by two spatially separated identical wavepackets. A set of equations governing the dynamics of the photon distribution in the configuration-momentum space is derived and solved. It is shown that the distribution function can be negative that manifests its quasiprobability nature. A spectrum of the reflected light is found to be narrower than that of the transmitted light that features a pronounced filtering effect. Average numbers of the transmitted and reflected photons and their variances are shown to be dependent not only on the pulse widths and the light-TLS interaction but also on the pulse separation that can serve as an effective controlling parameter. Our approach is generalized for the case of an n-photon Fock state.

quant-ph↗