arXiv subjects

V. S. Starovoitov

Publications and source records attributed to V. S. Starovoitov.

8 recordsLinked to original sources

arXiv2024

Frame-filtered ghost imaging with a SPAD array used both as a multiple "bucket" detector and an imaging camera

An approach to ghost imaging with a single SPAD array used simultaneously as a several-pixel "bucket" detector and an imaging camera is described. The key points of the approach are filtering data frames used for ghost-image reconstruction by the number of per-frame counts and superposing correlation images obtained for different "bucket" pixels. The imaging is performed in an experiment with a pseudo-thermal light source where the light intensity is so low that the dark counts have a noticeable effect on imaging. We demonstrate that the approach is capable to significantly reduce the destructive effect of dark counts on the ghost image and improve image contrast, spatial resolution, and image similarity to a reference image.

physics.optics↗

arXiv2014

A compact resonant Π-shaped photoacoustic cell with low window background for gas sensing

A resonant photoacoustic cell capable of detecting the traces of gases at an amplitude-modulation regime is represented. The cell is designed so as to minimize the window background for the cell operation at a selected acoustic resonance. A compact prototype cell (the volume of acoustic cavity of ~ 0.2 cm^3, total cell weight of 3.5 g) adapted to the narrow diffraction-limited beam of near-infrared laser is produced and examined experimentally. The noise-associated measurement error and laser-initiated signals are studied as functions of modulation frequency. The background signal and useful response to light absorption by the gas are analyzed in measurements of absorption for ammonia traces in nitrogen flow with the help of a pigtailed DFB laser diode operated near a wavelength of 1.53 um. The performance of absorption detection and gas-leak sensing for the prototype operated at the second longitudinal acoustic resonance (the resonance frequency of ~ 4.38 kHz, Q-factor of ~ 13.9) is estimated. The noise-equivalent absorption normalized to laser-beam power and detection bandwidth is ~ 1.44x10^{-9} cm^{-1} W Hz^{-1/2}. The amplitude of the window-background signal is equivalent to an absorption coefficient of ~ 2.82x10^{-7} cm^{-1}.

physics.optics↗

arXiv2013

A Miniaturized Prototype of Resonant Banana-Shaped Photoacoustic Cell for Gas Sensing

A resonant photoacoustic cell intended for laser-spectroscopy gas sensing is represented. This cell is a miniature imitation of a macro-scale banana-shaped cell developed previously. The parameters, which specify the cavity shape, are chosen so as not only to provide optimal cell operation at a selected acoustic resonance but also to reduce substantially the cell sizes. A miniaturized prototype cell (the volume of acoustic cavity of ~ 5 mm^3) adapted to the narrow diffraction-limited beam of near-infrared laser is produced and examined experimentally. The noise-associated measurement error and laser-initiated signals are studied as functions of modulation frequency. The background signal and the useful response to light absorption by the gas are analyzed in measurements of absorption for ammonia in nitrogen flow with the help of a pigtailed DFB laser diode oscillated near a wavelength of 1.53 um. The performance of prototype operation at the second longitudinal acoustic resonance (the resonance frequency of ~ 32.9 kHz, Q-factor of ~ 16.3) is estimated. The noise-limited minimal detectable absorption normalized to laser-beam power and detection bandwidth is ~ 8.07*10^(-8) cm^(-1) W Hz^(-1/2). The amplitude of the background signal is equivalent to an absorption coefficient of ~ 2.5*10^(-5) cm^(-1). Advantages and drawbacks of the cell prototype are discussed. Despite low absorption-sensing performance, the produced miniaturized cell prototype shows a good capability of gas-leak detection.

physics.optics↗

arXiv2009

Small-Size Resonant Photoacoustic Cell of Inclined Geometry for Gas Detection

A photoacoustic cell intended for laser detection of trace gases is represented. The cell is adapted so as to enhance the gas-detection performance and, simultaneously, to reduce the cell size. The cell design provides an efficient cancellation of the window background (a parasite response due to absorption of laser beam in the cell windows) and acoustic isolation from the environment for an acoustic resonance of the cell. The useful photoacoustic response from a detected gas, window background and noise are analyzed in demonstration experiments as functions of the modulation frequency for a prototype cell with the internal volume ~ 0.5 cm^3. The minimal detectable absorption for the prototype is estimated to be ~ 1.2 10^{-8} cm^{-1} W Hz^{-1/2}.

physics.optics↗

arXiv2008

Application of a miniaturized photoacoustic cell for high-sensitivity laser detection of ammonia in gas media

We present a photoacoustic resonant cell, the internal volume of which is ~ 0.5 cm^3. The cavity shape of the cell is so adapted in order to minimize the background signal arising due to absorption of laser beam in the cell windows. An experimental setup, measurement procedure and design of the cell are described. Results of detection of ammonia in nitrogen flow with the help of a CO2-laser are represented. The minimal detectable absorption for the cell is estimated in the experiment to be ~ 5.1 10^(-8) cm^(-1) W Hz^(-1/2)

physics.optics↗

arXiv2002

Local Spectral Density for a Periodically Driven System of Coupled Quantum States with Strong Imperfection in Unperturbed Energies

A random matrix theory approach is applied in order to analyze the localization properties of local spectral density for a generic system of coupled quantum states with strong static imperfection in the unperturbed energy levels. The system is excited by an external periodic field, the temporal profile of which is close to monochromatic one. The shape of local spectral density is shown to be well described by the contour obtained from a relevant model of periodically driven two-states system with irreversible losses to an external thermal bath. The shape width and the inverse participation ratio are determined as functions both of the Rabi frequency and of parameters specifying the localization effect for our system in the absence of external field.

quant-ph↗

arXiv2002

A Diffusion-Based Approach to Geminate Recombination of Heme Proteins with Small Ligands

A model of postphotodissociative monomolecular (geminate) recombination of heme proteins with small ligands (NO, O2 or CO) is represented. The non-exponential decay with time for the probability to find a heme in unbound state is interpreted in terms of diffusion-like migration of ligabs physics/0212040 and between protein cavities. The temporal behavior for the probability is obtained from numerical simulation and specified by two parameters: the time τ_{reb} of heme-ligand rebinding for the ligand localized inside the heme pocket and the time τ_{esc} of ligand escape from the pocket. The model is applied in the analysis of available experimental data for geminate reoxygenation of human hemoglobin HbA. Our simulation is in good agreement with the measurements. The analysis shows that the variation in pH of the solution (6.0<pH<9.4) results in considerable changes for τ_{reb} from 0.36 ns (at pH=8.5) up to 0.5 ns (pH=6.0) but effects slightly on the time τ_{esc} (τ_{esc} ~ 0.88 ns).

physics.bio-ph↗

arXiv2002

Ergodic Properties of Local Spectral Density for a Conservative System of Coupled Quantum States

The shape and the inverse participation ratio (IPR) of local spectral density (LSD) are studied for a generic isolated system of coupled quantum states, the Hamiltonian of which is represented by a band random matrix with the disordered leading diagonal. We find for the matrices with arbitrary small band that the lack of ergodicity for LSD can be associated with an exponential increase in IPR with the ratio $v/Δ_c$ ($v$ - the root of mean square for off-diagonal matrix elements, $Δ_c$ - the energy spacing between directly coupled basis states). Criterions specifying transition to localization and ergodicity for LSD are considered.

quant-ph↗