arXiv subjects

R. N. Shakhmuratov

Publications and source records attributed to R. N. Shakhmuratov.

18 recordsLinked to original sources

arXiv2022

Space-time analogy and its application to design schemes borrowed from Fourier optics for processing ultrafast optical signals

Square-wave pulse generation with a variable duty ratio can be realized with the help of ideas of Talbot array illuminators formulated for binary phase gratings. A binary temporal phase modulation of CW laser field propagating through a group-delay-dispersion circuit of the fractional Talbot length $P/Q$ results in a well defined sequence of square-wave-form pulses. When $P=1$ a duty ratio of the pulses $D$ is $1/2$ for $Q=4$ and $1/3$ for $Q=3$ and 6. Maximum intensity of the pulses doubles and triples compared to the CW intensity for $D=1/2$ and $1/3$, respectively. These pulses can be used for return-to-zero laser field modulation in optical fiber communication. For $D=1/3$ extra features between the pulses are found originating from a finite rise and drop time of phase in a binary phase modulation. Similar effect as a benefit of the time-space analogy is predicted for binary phase gratings and interpreted as gleams produced by imperfect edges of the components of the rectangular phase gratings.

physics.optics↗

arXiv2020

Powder vibration studied by Mössbauer spectroscopy

Mössbauer spectroscopy is applied to study ultrasound vibration of a granular material. A pile of powder is placed onto the surface of piezo transducer vibrated with the frequency 12.68 MHz. The size of grains (1.3 $μ$m) is much smaller than the wavelength of ultrasound, but much larger than the vibration amplitude. Due to vibration a single line of the Mössbauer transmission spectrum is split into a comb structure with a period equal to the vibration frequency. This spectrum contains the information about fast and slow modes in granular dynamics. We developed a method which allows to measure decay of ultrasound in the granular material and to estimate the results of the particle convection of grains in the pile.

cond-mat.soft↗

arXiv2020

Increasing efficiency of quantum memory based on atomic frequency combs

A protocol, which essentially increases the efficiency of the quantum memory based on the atomic frequency comb (AFC), is proposed. It is well known that a weak short pulse, transmitted trough a medium with a periodic structure of absorption peaks separated by transparency windows (AFC), is transformed into prompt and delayed pulses. Time delay is equal to the inverse value of the frequency period of the peaks. It is proposed to send the prompt pulse again through the medium and to make both delayed pulses to interfere. This leads to the essential increase of the efficiency of the AFC storage protocol.

quant-ph↗

arXiv2020

Application of Mössbauer spectroscopy to study vibrations of a granular medium excited by ultrasound

It is shown that analysis of Mössbaur spectra of a granulated medium, immersed into the epoxy resin without hardener, allows to study mechanical vibrations of granules. In our experiments, small particles of the potassium ferrocyanide with a 1.25 micron mean size played a role of granules. This compound was enriched by $^{57}$Fe isotope. Particle vibrations in the vibrated resin with the frequency 12.72 MHz were induced by piezo polymer film. At rest, Mössbauer spectrum of $^{57}$Fe in the potassium ferrocyanide consists of a single line. Ultrasonic vibration of nuclei splits the line into a comb structure with a period equal to the vibration frequency. The spectrum analysis allows to estimate the vibration amplitude of particles and decay of the ultrasound in this medium. The proposed method is unique since it allows to measure subangstrom displacements of particles vibrating with several MHz frequency.

cond-mat.soft↗

arXiv2019

Pulse shaping by a frequency filtering of a sawtooth phase-modulated CW laser

The spectrum of a CW field whose phase experiences a periodic sawtooth modulation is analyzed. Two types of the sawtooth phase modulation are considered. One is created by combining many harmonics of the fundamental frequency. The second is produced by electro-optic modulator fed by the relaxation oscillator, which generates a voltage slowly rising during charging the energy storage capacitor and dropping fast due to discharge by a short circuit. It is proposed to filter out the main spectral component of the sawtooth phase modulated field. This filtering produces short pulses from CW phase modulated field. Several filters are proposed to remove the selected spectral component. It is shown that such a filtering is capable to produce a train of short pulses. Duty cycle of this train is equal to the modulation period and duration of the pulses can vary from $10^{-1}$ to $10^{-2}$ of the period. Depending on the modulation frequency, the proposed method is capable to produce pulses with duration ranging from nanoseconds to a fraction of picosecond.

physics.optics↗

arXiv2018

Frequency crystal

Pulse filtering through a medium with infinite periodic structure in transmission spectrum is analyzed. Two types of filters are considered. The first, named harmonic frequency crystal (HFC), is the filter whose widths of transmitting and absorbing windows are equal. The second, named anharmonic frequency crystal (AHFC), has narrow absorption peaks separated by wide transmission windows. AHFC of moderate optical thickness demonstrates properties quite similar to those of high finesse atomic frequency comb (AFC) with limited number of the absorption peaks, which produce a few pulses from a short input pulse. On the contrary, HFC transforms the input pulse into a train of pulses whose maximum amplitudes follow a wide bell-shaped envelope. HFC allows to find an exact universal analytical solution, which describes transformation of a broadband pulse into a train of short pulses, slow light propagation for a pulse whose spectral width fits one of the transparency windows of the crystal, and absorption typical for a single line absorber if the pulse spectrum falls into one of the absorption peaks. Potential applications of HFC are discussed.

physics.optics↗

arXiv2017

Time-delayed coincidence technique for subnatural-width spectroscopy as an interference phenomenon

Single photon, emitted in a transition between two states, has a frequency distribution of intensity, which is given by Lorentzian if the transition is only naturally broadened and the period of observation $T$ is long compared to the lifetime $T_{1}$ of the excited state. However, when the observation time $T$ is short or comparable to $T_{1}$, the frequency spectrum is appreciably broadened. If only the delayed part of the emitted radiation field is detected, then the radiation spectrum does not change. However, if the radiation field is transmitted through a resonant absorber and then detected, the absorption/transmission spectrum of the delayed radiation field is narrowed. We show that this narrowing is due to the interference of the spectral components of the field. Experimental spectra of absorption of Mössbauer radiation, obtained by coincidence technique, confirm this conclusion.

physics.optics↗

arXiv2016

Application of Mössbauer effect to study subnanometer harmonic displacements in a thin solid

We measure subnanometer displacements of thin samples vibrated by piezotransducer. Samples contain $^{57}$Fe nuclei, which are exposed to 14.4 keV $γ$-radiation. Vibration produces sidebands from a single absorption line of the sample. The sideband intensities depend on the vibration amplitude and its distribution along the sample. We developed a model of this distribution, which adequately describes the spectra of powder and stainless steel (SS) absorbers. We propose to filter $γ$-radiation through a small hole in the mask, placed before the absorber. In this case only a small spot of the vibrated absorber is observed. We found for SS foil that nuclei, exposed to $γ$-radiation in this small spot, vibrate with almost the same amplitudes whose difference does not exceed a few picometers.

cond-mat.mes-hall↗

arXiv2016

Transformation of the frequency-modulated continuous-wave field into a train of short pulses by resonant filters

The resonant filtering method transforming frequency modulated radiation field into a train of short pulses is proposed to apply in optical domain. Effective frequency modulation can be achieved by electro-optic modulator or by resonant frequency modulation of the filter with a narrow absorption line. Due to frequency modulation narrow-spectrum CW radiation field is seen by the resonant filter as a comb of equidistant spectral components separated by the modulation frequency. Tuning narrow-bandwidth filter in resonance with $n$-th spectral component of the comb transforms the radiation field into bunches of pulses with $n$ pulses in each bunch. The transformation is explained by the interference of the coherently scattered resonant component of the field with the whole comb. Constructive interference results in formation of pulses, while destructive interference is seen as dark windows between pulses. It is found that the optimal thickness of the resonant filter is several orders of magnitude smaller than the necessary thickness of the dispersive filters used before in optical domain to produce short pulses from the frequency modulated field.

quant-ph↗

arXiv2015

Application of the low finesse frequency comb for high resolution spectroscopy

High finesse frequency combs (HFC) with large ratio of the frequency spacing to the width of the spectral components have demonstrated remarkable results in many applications such as precision spectroscopy and metrology. We found that low finesse frequency combs having very small ratio of the frequency spacing to the width of the spectral components are more sensitive to the exact resonance with absorber than HFC. Our method is based on time domain measurements reviling oscillations of the radiation intensity after passing through an optically thick absorber. Fourier analysis of the oscillations allows to reconstruct the spectral content of the comb. If the central component of the incident comb is in exact resonance with the single line absorber, the contribution of the first sideband frequency into oscillations is exactly zero. We demonstrate this technique with gamma-photon absorbtion by Mössbauer nuclei providing the spectral resolution beyond the natural broadening.

physics.optics↗

arXiv2015

Conversion of recoilless gamma-radiation into a periodic sequence of ultrashort pulses in a set of dispersive and absorptive resonant media

An efficient technique to produce a periodic sequence of ultrashort pulses of recoilless gamma-radiation via its transmission through the optically thick vibrating resonant absorber was demonstrated recently [Nature, 508, 80 (2014)]. In this work we extend the theoretical analysis to the case of a set of multiple absorbers. We consider an analytical model describing the control of spectral content of a frequency modulated gamma-radiation by selective correction of amplitudes and initial phases of some spectral components, using, respectively, the resonant absorption or dispersion of nuclei. On the basis of the analytical solutions we determine the ultimate possibilities of the proposed technique.

physics.optics↗

arXiv2014

Transformation of a single photon field into bunches of pulses

We propose a method to transform a single photon field into bunches of pulses with controllable timing and number of pulses in a bunch. This method is based on transmission of a photon through an optically thick single-line absorber vibrated with a frequency appreciably exceeding the width of the absorption line. The spectrum of the quasi-monochromatic incoming photon is 'seen' by the vibrated absorber as a comb of equidistant spectral components separated by the vibration frequency. Tuning the absorber in resonance with m-th spectral component transforms the output radiation into bunches of pulses with m pulses in each bunch. We experimentally demonstrated the proposed technique with single 14.4 keV photons and produced for the first time gamma-photonic time-bin qudits with dimension d=2m.

quant-ph↗

arXiv2013

Transformation of subradiant state to superradiant state in a thick resonant medium

The propagation of a step pulse through a thick resonant absorber with homogeneously broadened absorption line is considered. It is shown that a specific subradiant state is naturally developed in the absorber due to the formation of the spatial domains of the atomic coherence with opposite phases. It is proposed to divide the absorber into slices in accord with these domains and place the phase shifters in front of the first slice and between the other slices. If the phase shifters are switched on simultaneously at a particular moment of time, elapsed from the beginning of the step pulse, a strong sharp pulse is generated at the output of the last slice of the absorber. The effect is explained by the phasing of the atomic coherence along all slices of the absorber, which transforms subradiant state of atom-field system to superradiant state.

quant-ph↗

arXiv2013

Coherent Control of the Waveforms of Recoilless Gamma-Photons

An efficient method to coherently control the waveforms of gamma-photons has been proposed and experimentally realized. It is based on the resonant interaction of gamma-photons with an ensemble of nuclei with modulated frequency of the quantum transition. In particular, the temporal compression of an individual gamma-photon into coherent ultrashort pulse train has been demonstrated. The developed technique is expected to give a strong impetus on emerging fields of coherent and quantum gamma-optics, providing a basis for realization of the gamma-photon nuclear-ensemble interfaces and quantum interference effects at the nuclear gamma-ray transitions.

quant-ph↗

arXiv2007

Instantaneous processing of "slow light": amplitude-duration control, storage, and splitting

Nonadiabatic change of the control field or of the low-frequency coherence allows for an almost instantaneous change of the signal field propagating in a thick resonant absorber where electromagnetically induced transparency is realized. This finding is applied for the storage and retrieval of the signal, for the creation of a signal copy and separation of this copy from the original pulse without its destruction.

quant-ph↗

arXiv2006

A single photon emitted by a single particle in free space vacuum modes and its resonant interaction with two- and three-level absorbers

We consider the time-delayed coincidence counting of two photons emitted in a cascade by a single particle (atom, molecule, nucleus, etc). The time-dependence of the probability amplitude of the second photon in the cascade has a sharply rising leading edge due to the detection of the first photon, as results from causality. If a macroscopic ensemble of resonant two-level absorbers is placed in the path of the second photon between the radiation source and the detector, the photon absorption does not follow Beer's law due to the time-asymmetric shape of the photon. For very short delay times almost no absorption takes place, even in an optically dense medium. We analyze the propagation of such a second photon in a thick resonant three-level absorber if a narrow electromagnetically induced transparency (EIT) window is present at the center of the absorption line. It is shown that the EIT medium can change the asymmetric time dependence of the photon probability amplitude to a bell shape (EIT filtering). This bell-shaped photon interacts much more efficiently with an other ensemble of two-level absorbers chosen, for example, to store this photon and the information it carries.

quant-ph↗

arXiv2003

Adiabatic following criterion, estimation of the nonadiabatic excitation fraction and quantum jumps

An accurate theory describing adiabatic following of the dark, nonabsorbing state in the three-level system is developed. An analytical solution for the wave function of the particle experiencing Raman excitation is found as an expansion in terms of the time varying nonadiabatic perturbation parameter. The solution can be presented as a sum of adiabatic and nonadiabatic parts. Both are estimated quantitatively. It is shown that the limiting value to which the amplitude of the nonadiabatic part tends is equal to the Fourier component of the nonadiabatic perturbation parameter taken at the Rabi frequency of the Raman excitation. The time scale of the variation of both parts is found. While the adiabatic part of the solution varies slowly and follows the change of the nonadiabatic perturbation parameter, the nonadiabatic part appears almost instantly, revealing a jumpwise transition between the dark and bright states. This jump happens when the nonadiabatic perturbation parameter takes its maximum value.

physics.optics↗

arXiv2002

Stimulated Nutation Echo: Dynamic and Decay Properties

We study experimentally the dynamical and decay properties of the Stimulated Nutation Echo (SNE) in a two-level spin system. This is the signal which appears in the transient response of the system to the second pulse at time tau_1 elapsed from its beginning and coinciding with the duration of the first pulse. The information about the first pulse duration is imprinted into the population difference of the inhomogeneously broadened ensemble of the two-level absorbers. The decay of the SNE signal has two contributions. One originates from the population decay during the time tau between the pulses. Another is caused by the coherence loss during the excitation by the first pulse and the reading time of the second pulse. Experimental results on the decay properties induced by these mechanisms are presented. The dependence of these decay rates on the pulse intensity is discussed, and its relationship with the anomalous (non-Bloch) decay of other coherent transients in solids is examined.

physics.atom-ph↗