arXiv subjects
Publications and source records attributed to G. G. Kozlov.
The intensity noise spectrum of the light passed through an optical microcavity is calculated with allowance for thermal fluctuations of its thickness. The spectrum thus obtained reveals a peak at the frequency of acoustic mode localized inside the microcavity and depends on the size of the illuminated area. The estimates of the noise magnitude show that it can be detected using the up-to-date noise spectroscopy technique.
The perturbation theory is developed for joint statistics of the advanced and retarded Green's functions of the 1D Schrodinger equation with a piecewise-constant random potential. Using this method, analytical expressions are obtained for spectral dependence of the degree of localization and for the limiting (at $t\rightarrow\infty$) probability to find the particle at the point it was located at $t = 0$ (Andeson criterion). Definition of the localization length is introduced. The computer experiments confirming correctness of the calculations are described.
A comparative analysis of two approaches to description of the light modulation pulse delay in a saturable absorber is presented. According to the simplest model, the delay of the optical pulse is a result of distortion of its shape due to absorption self-modulation in the nonlinear medium. The second model of the effect, proposed at the beginning of our century, connects the pulse delay with the so-called "slow light" resulting from the group velocity reduction under conditions of the coherent population oscillations. It is shown that all the known experimental data on the light pulse delay in saturable absorbers can be comprehensively described in the framework of the simplest model of saturable absorber and do not require invoking the effect of coherent population oscillations with spectral hole-burning and anomalous modifications of the light group velocity. It is concluded that the effect of group velocity reduction under conditions of coherent population oscillations has not received so far any experimental confirmation, and the assertions about real observation of the "slow light" based on this mechanism are groundless.
The effect of the light group velocity reduction in dielectric Bragg reflection waveguide structures (SiO$_2$/TiO$_2$) in the vicinity of the cutoff frequency is studied experimentally. The effect of anti-mirror reflection, specific for the Bragg reflection waveguides, is described and employed for detection of "slow light". The experiments were performed with the use of the Ti:sapphire laser pulses ~ 100 fs in length. The group index $n_g \sim$ 30 with a fractional pulse delay (normalized to the pulse width) of $\sim$ 10 is demonstrated. The problems and prospects of implementation of the slow-light devices based on the Bragg reflection waveguide structures are discussed.
We show experimentally that the effects of "slow and fast light" that are considered to be caused by spectral hole-burning under conditions of coherent population oscillations (CPO) can be universally observed with incoherent light fields on objects with the pure-intensity nonlinearity, when such an interpretation is inapplicable. As a light source, we used an incandescent lamp and as objects for study, a photochromic glass and a thermochromic coating. The response of the objects to intensity modulation of the incident light reproduced in all details the commonly accepted experimental evidences of the "light with a negative group velocity" and "ultraslow light". We come to conclusion that so far there are no experimental works providing evidence for real observation of the "CPO-based slow or fast light".
One-dimensional defect photonic crystal (Bragg waveguide) is studied from the viewpoint of the slow light problem. The calculations are presented showing that in the TiO$_2$/SiO$_2$-based Bragg waveguide one can obtain the group index of $\sim$ 1000 and spatial decay length of $\sim$ 3 mm for a nanosecond-scale pulse. Distortion of the pulse due to the group index dispersion proves to be acceptable for the relative pulse delay not exceeding 10. We also analyze propagation of the light pulse in the Bragg waveguide with a quantum well inside and provide arguments showing possibility of reaching the group index of $\sim$ 10000. To the best of our knowledge, analysis of pulse propagation in a Bragg waveguide in connection with the slow light problem has not been performed so far. We will still much appreciate any information about such studies, if any.
For a one dimensional half-infinite chain with diagonal disorder we calculated the ultimate at $t\to\infty$ value of the average excitation density at the edge site $D$ if at $t=0$ the excitation was localised at the edge site (Anderson' s creterium). We obtained the following results: i) for the binary disordered chain we derived the close expression for $D$ which is exact in the limit of low concentration of defects and is valid for an arbitrary energy of defects $\varepsilon$. In this case $D$ demonstrated the non analytical dependence on $\varepsilon$. ii) The close expression for $D$ is obtained for the case of an arbitrary small disorder. iii) The relative contribution of states with specified energy to $D$ is calculated. All the results obtained are in complete agreement with computer simulation.
The question is raised about whether the pulse delay in a saturable absorber has anything to do with the "slow light" and group velocity reduction. We also wonder why the 40-years-old trivial interpretation of the effect remains so far ignored.
We solve exactly the spectral problem for the non-Hermitian operator $H_U f(x)\equiv f(U-1/x)/x^2$. Despite the absence of orthogonality, the eigen functions of this operator allow one to construct in a simple way the expansion of an arbitrary function in series. Explicit formulas for the expansion coefficients are presented. This problem is shown to be connected with that of calculating the strange attractor's density for the map $x_{n+1}=1/(U-x_n)$. The explicit formula for the strange attractor's density for this map is derived. All results are confirmed by direct computer simulations.
Simple algorithm of dynamics of Ising magnetic is described. The algorithm can be implemented on conventional digital computer and can be used for construction of specialized processor for simulation of ferromagnetic systems. The algorithm gives a simple way to calculate 1D correlation functions for 1D Ising magnetic.
For the model Hamiltonian describing the electron-nuclear dynamics of a quantum dot, we obtained an exact expression for the limiting nuclear polarization as a function of the number of groups of equivalent nuclei. It is shown that the refinement of the model Hamiltonian by increasing the number of the groups results in a slow growth of the limiting nuclear polarization. This allowed us to put forward arguments in favor of applicability of the box-model (with all the nuclei being equivalent) for description of the electron-nuclear spin dynamics within the time intervals of around hundreds of periods of the optical orientation.
It is shown that the effect of hole-burning under conditions of coherent population oscillations as well as the light pulse delay in a saturable absorber (a modification of the "slow light" effect) can be interpreted, in a comprehensive way, in terms of {\it intensity spectrum} of the light and {\it intensity-related susceptibility} of the non-linear medium. The physical content of these effects is illustrated by a simple electric circuit with a non-linear resistor which realizes a full analog of the saturable absorber. In this case the effect of hole-burning in the absorption spectrum of the medium is converted in to the effect of hole-burning in the frequency dependence of resistance of the non-linear resistor and the effect of "slow light" -- in to the effect of "slow current".
The model considered in the paper is used nowadays to describe spin dynamics of quantum dots after optical excitation. Based on the exact diagonalization of a model Hamiltonian, we solve the problems of the electron spin polarization decay and magnetic field dependence of the steady state polarization. The important role of the nuclear state is shown and methods of its calculation for different regimes of optical excitation are proposed. The effect of spin echo observed after application of the magnetic field $π$-pulse is predicted.
A simple method for visualization of nonuniformity of planar MBE structures is proposed. The method is based on measuring the relief of the photo-EMF. The method can be applied to a wide variety of semiconductor structures and does not require any expensive equipment.
The atoms moving within the waveguide with a critical frequency higher than the resonant frequency of atoms are suggested for obtaining the "slow light". Due to the absence of the resonant mode in the guide the atoms conserves excitation and coherence. The speed of this mixed excitation (electromagnetic field + moving atom) can be very low or even zero. The atoms moving within the waveguide with a critical frequency higher than the resonant frequency of atoms are suggested for obtaining the "slow light". Due to the absence of the resonant mode in the guide the atoms conserves excitation and coherence. The speed of this mixed excitation (electromagnetic field + moving atom) can be very low or even zero.
The paper presents a critical analysis of publications devoted to one of the methods for production of the so-called "slow light" (the light with an anomalously low group velocity) due to extremely high local steepness of the dispersion curve of the medium. The method in point employs for this purpose the effect of coherent population oscillations accompanied by burning of a narrow spectral hole in the homogeneously broadened absorption spectrum. Physical model of the effect proposed in the studies under consideration is based on analysis of response of a nonlinear medium to a low-frequency intensity modulation of the incident light beam. We show that all the observations described in these papers can be easily interpreted in the framework of the simplest model of saturable absorber and have nothing to do with the effects of hole burning and group velocity reduction.
It is shown that the monochromatic optical wave propagating through the medium with linear birefringence in presence of a signal electromagnetic wave (whose wavelength is equal to the polarization beats length), displays Faraday rotation having the frequency of the signal wave and unsuppressed by linear birefringence. The effect is resonant with respect to the frequency of a signal wave. The "sharpness" of the resonance is defined by length of the birefringent medium.
It is shown that the light scattered by a finite 2D crystal strip in the region of an exciton resonance should display strong backscattering. This phenomenon is related to the exciton reflection from the edge of the strip.