Search

Currently, the Kurchatov Laser−Synchrotron Complex is conducting research on the interaction of powerful femtosecond laser radiation with matter. The purpose of these studies is to develop new techniques and approaches for the characterization of high−temperature plasma, X−rays and particle acceleration, which can be the basis for the work planned within the framework of the synchrotron−neutron project. Laser−driven X−ray production, electron acceleration, nuclear fusion, ultrafast structural dynamics of nanoparticles in intense laser fields remains an active research topic, aimed at generating advanced controllable sources.

Quantum memory based on a system of resonators each containing one atom and connected to an external waveguide through a common resonator has been proposed. The parameters of the resonators and atoms interacting with them at which the effective transfer of a single-photon signal wave packet from the external waveguide to atomic states for long-term storage of the quantum state of the photon have been determined using reversible properties of the dynamics of the system under study and optimization methods. The advantages of quantum memory under consideration, as well as experimental possibilities of its implementation, have been discussed.

Ultrafast nonlinear dynamics driven by high-peak-power ultrashort mid-infrared (mid-IR) pulses gives rise to ultrabroadband radiation whose spectrum spans over multiple decades, stretching from the terahertz (THz) to the microwave range. We show that, despite its enormous, multidecade bandwidth, an accurate spectral and spatial-mode characterization of this radiation is possible via a suitable combination of mutually complementary signal-analysis methods borrowed from ultrafast optics, radio electronics, THz photonics, and microwave engineering. This analysis reveals intense subgigahertz radiation emitted as a part of mid-IR-driven supercontinuum generation and shows that microwave-to-THz field waveforms can almost reach the diffraction limit in their beam focusability, yielding field strengths above 3 MV/cm.

We demonstrate how the Hong-Ou-Mandel (HOM) interference with polarization-entangled photons can be used to probe ultrafast dephasing. We can infer the optical properties like the real and imaginary parts of the complex susceptibility of the medium from changes in the position and the shape of the HOM dip. From the shift of the HOM dip, we are able to measure 22 fs dephasing time using a continuous-wave (CW) laser even with optical loss > 97%, while the HOM dip visibility is maintained at 92.3~\% (which can be as high as 96.7%). The experimental observations, which are explained in terms of a rigorous theoretical model, demonstrate the utility of HOM interference in probing ultrafast dephasing., 12 pages, 7 figures

We demonstrate an adaptive wave-front shaping of optical beams transmitted through fiber bundles as a powerful resource for multisite, high-resolution bioimaging. With the phases of all the beamlets delivered through up to 6000 different fibers within the fiber bundle controlled individually, by means of a high-definition spatial light modulator, the overall beam transmitted through the fiber bundle can be focused into a beam waist with a diameter less than 1 μm within a targeted area in a biotissue, providing a diffraction-limited spatial resolution adequate for single-cell or even subcellular bioimaging. The field intensity in the adaptively-focused continuous-wave laser beam in our fiber-bundle-imaging setting is more than two orders of magnitude higher than the intensity of the speckle background. Once robust beam focusing was achieved with a suitable phase profile across the input face of the fiber bundle, the beam focus can be scanned over a targeted area with no need for a further adaptive search, by applying a physically intuitive, wave-front-tilting phase mask on the field of input beamlets. This method of beam-focus scanning promises imaging speeds compatible with the requirements of in vivo calcium imaging.

Modern optical physics provides means to detect and resolve ultrafast processes on a time scale of tens of attoseconds. The physical interpretation of such measurements, however, remains the focus of heated debate. In its conceptual dimension, this debate reflects fundamental difficulties in defining time in quantum mechanics. En route toward resolving this difficulty, we are led to extend universal uncertainty relations to ultrafast light–matter interactions. Such a generalized uncertainty sets a lower bound on the response time inherent in attosecond electronic dynamics driven by ultrashort laser pulses, dictating a speed limit for next-generation photonic information systems — systems of petahertz optoelectronics.

We investigate quantum beats by monitoring cooperative emission from rubidium vapor and demonstrate correlated beats via coupled emission channels. We develop a theoretical model, and our simulations are in good agreement with experimental results. The results pave the way for advanced techniques measuring interactions between atoms that are excited to high energy levels.

The smallness of the velocity $$v$$ of laser-field-induced motion of electrons compared to the speed of light c is one of the fundamental physical factors limiting the efficiency of nonlinear optical processes in plasma media. It has been shown in this work that the use of intense ultrashort mid-infrared pulses makes it possible to significantly enhance a wide class of $$v{\text{/}}c$$ -weak plasma nonlinearities primarily related to plasma currents induced by the laser field. This allows implementing laser plasma schemes of the efficient generation of coherent broadband terahertz and microwave radiation, i.e., terahertz–microwave supercontinuum.

The effect of laser radiation with a wavelength near 1.55 µm on the photoluminescence properties of “nitrogen-vacancy” (NV) color centers in diamond has been studied experimentally. The effect of radiation of an infrared laser on the charge state of color centers redistributes the spectral intensity of photoluminescence in the ensemble of NV centers. In the case of neutral NV centers, the quenching of photoluminescence reaching about 60% has been observed. A feature of the laser excitation of NV centers by this method is the absence of competition with stimulated emission and two-photon excitation, which is observed with an increase in the power of infrared radiation at other wavelengths.

We present all-optical high-resolution temperature measurements in the brain of freely behaving mice using an implantable thermometer that integrates a reconnectable two-section fiber-optic probe a...

Thermogenetics appeared recently as an evolutionary advance in methods of optical stimulation of nerve cells and uses focused light to activate light-sensitive cation channels in the neuron membrane. Light activation and opening of light-sensitive channels, which can be expressed genetically in any type of neuron, induces neuron membrane depolarization and a resultant action potential. In contrast to classical methods of optogenetics, which use the visible spectrum, thermogenetics uses channels sensitive to warming. This provides the opportunity for additional activation of these channels not only using IR light, but also other methods of warming nervous tissue, such as ultrasound or microwave radiation. The penetrability of living tissue to stimulation with IR radiation is an order of magnitude greater than that for visible spectrum radiation, which allows thermogenetics methods to be used in vivo without invasive surgical methods to “clear the way” for optogenetic stimulation. On the other hand, the thermal nature of the stimulation imposes additional limits on use of the method, as heating must be sufficiently gentle so as not to induce heat shock at the cellular level, and the threshold of activation must be sufficiently high for channel opening not to occur spontaneously at normal physiological temperatures.

Dr Deborah Birx, the White House Coronavirus Task Force coordinator, told NBC News on "Meet the Press"that "[T]he U S needs a 'breakthrough' in coronavirus testing to help screen Americans and get a more accurate picture of the virus' spread "We have been involved with biopathogen detection since the 2001 anthrax attacks and were the first to detect anthrax in real-time A variation on the laser spectroscopic techniques we developed for the rapid detection of anthrax can be applied to detect the Severe Acute Respiratory Syndrome-Corona Virus-2 (SARS-CoV-2 virus) In addition to detecting a single virus, this technique allows us to read its surface protein structure In particular, we have been conducting research based on a variety of quantum optical approaches aimed at improving our ability to detect Corona Virus Disease-2019 (COVID-19) viral infection Indeed, the detection of a small concentration of antibodies, after an infection has passed, is a challenging problem Likewise, the early detection of disease, even before a detectible antibody population has been established, is very important Our team is researching both aspects of this problem The paper is written to stimulate the interest of both physical and biological scientists in this important problem It is thus written as a combination of tutorial (review) and future work (preview) We join Prof Federico Capasso and Editor Dennis Couwenberg in expressing our appreciation to all those working so heroically on all aspects of the COVID-19 problem And we thank Drs Capasso and Couwenberg for their invitation to write this paper © 2020 Navid Rajil et al , published by De Gruyter, Berlin/Boston 2020

Experiments on the generation of high optical harmonics demonstrating that relativistic regimes of interaction of radiation with matter can be implemented in the field of mid-infrared laser pulses with a peak power of 0.3 TW have been reported. The observation of relativistic phenomena at such extraordinary low peak powers of the laser field becomes possible because of the formation of a high-quality space-time mode of the laser field with an exactly specified polarization state. Such a field structure ensures a high intensity of radiation in the focus of the beam and the effective acceleration of electrons by a low-frequency electromagnetic field of a high-contrast laser pulse with an exactly specified polarization at the extremely sharp vacuum-solid interface.

Quantum entanglement is a powerful resource that revolutionizes information science, opens new horizons in communication technologies, and pushes the frontiers of sensing and imaging. Whether or not the methods of quantum entanglement can be extended to life-science imaging is far from clear. Live biological systems are eluding quantum-optical probes, proving, time and time again, too lossy, too noisy, too warm, and too wet to be meaningfully studied by quantum states of light. The central difficulty that puts the main roadblock on the path toward entanglement-enhanced nonlinear bioimaging is that the two-photon absorption (TPA) of entangled photons can exceed the TPA of uncorrelated photons only at the level of incident photon flux densities as low as one photon per entanglement area per entanglement time. This fundamental limitation has long been believed to rule out even a thinnest chance for a success of bioimaging with entangled photons. Here, we show that new approaches in nonlinear and quantum optics, combined with the latest achievements in biotechnologies, open the routes toward efficient photon-entanglement-based strategies in TPA microscopy that can help confront long-standing challenges in life-science imaging. Unleashing the full potential of this approach will require, however, high throughputs of virus-construct delivery, high expression efficiencies of genetically encodable fluorescent markers, high-brightness sources of entangled photons, as well as a thoughtful entanglement engineering in time, space, pulse, and polarization modes. We demonstrate that suitably tailored nonlinear optical fibers can deliver entangled photon pairs confined to entanglement volumes many orders of magnitude smaller than the entanglement volumes attainable through spontaneous parametric down-conversion. These ultracompact modes of entangled photons are shown to enable a radical enhancement of the TPA of entangled photons, opening new avenues for quantum entanglement in life-science imaging.

We identify experimental conditions for efficient generation of THz pulses by high power near IR laser radiation: 2 TW, 30 fs, 800-nm laser pulses with their second harmonic were slightly focused in a low-pressure gas cell in such a way to avoid multiple filamentation and excessive ionization. This two-color scheme yields a microjoule level of THz pulses which is two orders of magnitude higher than the signal generated in the atmosphere of ambient air.

We demonstrate a versatile framework for cellular brain imaging in awake mice based on suitably tailored segments of graded-index (GRIN) fiber. Closed-form solutions to ray-path equations for graded-index waveguides are shown to offer important insights into image-transmission properties of GRIN fibers, suggesting useful recipes for optimized GRIN-fiber-based deep-brain imaging. We show that the lengths of GRIN imaging components intended for deep-brain studies in freely moving rodents need to be chosen as a tradeoff among the spatial resolution, the targeted imaging depth and the degree of fiber-probe invasiveness. In the experimental setting that we present in this paper, the head of an awake mouse with a GRIN-fiber implant is fixed under a microscope objective, but the mouse is free to move around an in-house-built flat-floored air-lifted platform, exploring a predesigned environment, configured as an arena for one of standard cognitive tests. We show that cellular-resolution deep-brain imaging can be integrated in this setting with robust cell-specific optical neural recording to enable in vivo studies with minimal physical restraints on animal models. The enhancement of the information capacity of the fluorescence signal, achieved via a suitable filtering of the GRIN-fiber readout, is shown to open routes toward practical imaging modalities whereby the deep-brain neuronal dynamics and axonal connections underpinning the integrative functions of essential brain structures can be studied in awake rodent models.

We present an experimental framework and methodology for in vivo studies on rat stroke models that enable a real-time fiber-optic recording of stroke-induced hydrogen peroxide and pH transients in ischemia-affected brain areas. Arrays of reconnectable implantable fiber probes combined with advanced optogenetic fluorescent protein sensors are shown to enable a quantitative multisite time-resolved study of oxidative-stress and acidosis buildup dynamics as the key markers, correlates and possible drivers of ischemic stroke. The fiber probes designed for this work provide a wavelength-multiplex forward-propagation channel for a spatially localized, dual-pathway excitation of genetically encoded fluorescence-protein sensors along with a back-propagation channel for the fluorescence return from optically driven fluorescence sensors. We show that the spectral analysis of the fiber-probe-collected fluorescence return provides means for a high-fidelity autofluorescence background subtraction, thus enhancing the sensitivity of real-time detection of stroke-induced transients and significantly reducing measurement uncertainties in in vivo acute-stroke studies as inherently statistical experiments operating with outcomes of multiply repeated measurements on large populations of individually variable animal stroke models.

An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022340069

Integrated photonics will play a key role in quantum systems as they grow from few-qubit prototypes to tens of thousands of qubits. The underlying optical quantum technologies can only be realized through the integration of these components onto quantum photonic integrated circuits (QPICs) with accompanying electronics. In the last decade, remarkable advances in quantum photonic integration have enabled table-top experiments to be scaled down to prototype chips with improvements in efficiency, robustness, and key performance metrics. These advances have enabled integrated quantum photonic technologies combining up to 650 optical and electrical components onto a single chip that are capable of programmable quantum information processing, chip-to-chip networking, hybrid quantum system integration, and high-speed communications. In this roadmap article, we highlight the status, current and future challenges, and emerging technologies in several key research areas in integrated quantum photonics, including photonic platforms, quantum and classical light sources, quantum frequency conversion, integrated detectors, and applications in computing, communications, and sensing. With advances in materials, photonic design architectures, fabrication and integration processes, packaging, and testing and benchmarking, in the next decade we can expect a transition from single- and few-function prototypes to large-scale integration of multi-functional and reconfigurable devices that will have a transformative impact on quantum information science and engineering., JPhys Photonics, 4 (1), ISSN:2515-7647

Enhanced-resolution imaging in complex scattering media is revisited from a parameter estimation perspective. A suitably defined Fisher information is shown to offer useful insights into the limiting precision of parameter estimation in a scattering environment and, hence, into the limiting spatial resolution that can be achieved in imaging-through-scattering settings. The Fisher information that defines this resolution limit via the Cramér–Rao lower bound is shown to scale with the number of adaptively controlled space–time modes of the probe field, suggesting a physically intuitive generalization of the Abbe limit to the spatial resolution attainable for complex scattering systems. In a conventional, direct-imaging microscopy setting, this bound is shown to converge to the canonical Abbe limit.

We present a closed-form analytical description for the metrological performance of a generic superposition of spin coherent states (SSCS) used as probes for quantum phase estimation. Working in this framework, we derive transparent analytical expressions for the pertinent quantum Fisher information and identify a general class of spin coherent states enabling quantum metrology with Heisenberg-limit precision. Bloch-sphere analysis of antipodal SSCS shows that the phase-estimation precision attainable with such states increases with the distance from the equator of the Bloch sphere, growing from the shot-noise limit level for the equatorial states all the way up to the Heisenberg limit for SSCS that can be represented as superpositions of the poles of the Bloch sphere.

Ultrafast laser-plasma interactions driven by ultrashort terawatt laser pulses are shown to give rise to a bright multioctave microwave radiation, whose polarization and spatial mode structure provides a sensitive probe for laser-driven plasma electrodynamics, helping detect the symmetries of plasma currents and signatures of multiple ionization. Polarization mode structure of this radiation is dominated, as polarization-resolved measurements show, by a radially polarized mode, indicating the significance of ponderomotively driven plasma currents as sources of microwave emission. Angle-resolved analysis of microwave supercontinua reveals regimes in which the microwave emission is drastically enhanced, via coherence buildup, manifested in a well-resolved Cherenkov-emission cone.

We present a particle-in-cell (PIC) analysis of terahertz (THz) radiation by ultrafast plasma currents driven by relativistic-intensity laser pulses. We show that, while the I0$${\lambda }_{0}^{2}$$ λ 0 2 product of the laser intensity I0 and the laser wavelength λ0 plays the key role in the energy scaling of strong-field laser-plasma THz generation, the THz output energy, WTHz, does not follow the I0$${\lambda }_{0}^{2}$$ λ 0 2 scaling. Its behavior as a function of I0 and λ0 is instead much more complex. Our two- and three-dimensional PIC analysis shows that, for moderate, subrelativistic and weakly relativistic fields, WTHz(I0$${\lambda }_{0}^{2}$$ λ 0 2 ) can be approximated as (I0λ02)α, with a suitable exponent α, as a clear signature of vacuum electron acceleration as a predominant physical mechanism whereby the energy of the laser driver is transferred to THz radiation. For strongly relativistic laser fields, on the other hand, WTHz(I0$${\lambda }_{0}^{2}$$ λ 0 2 ) closely follows the scaling dictated by the relativistic electron laser ponderomotive potential $${\mathscr{F}}_{{\text{e}}}$$ F e , converging to WTHz ∝ $${I}_{0}^{1/2}{\lambda }_{0}$$ I 0 1 / 2 λ 0 for very high I0, thus indicating the decisive role of relativistic ponderomotive charge acceleration as a mechanism behind laser-to-THz energy conversion. Analysis of the electron distribution function shows that the temperature Te of hot laser-driven electrons bouncing back and forth between the plasma boundaries displays the same behavior as a function of I0 and λ0, altering its scaling from (I0λ02)α to that of $${\mathscr{F}}_{{\text{e}}}$$ F e , converging to WTHz ∝ $${I}_{0}^{1/2}{\lambda }_{0}$$ I 0 1 / 2 λ 0 for very high I0. These findings provide a clear physical picture of THz generation in relativistic and subrelativistic laser plasmas, suggesting the THz yield WTHz resolved as a function of I0 and λ0 as a meaningful measurable that can serve as a probe for the temperature Te of hot electrons in a vast class of laser–plasma interactions. Specifically, the α exponent of the best (I0λ02)α fit of the THz yield suggests a meaningful probe that can help identify the dominant physical mechanisms whereby the energy of the laser field is converted to the energy of plasma electrons.

Cherenkov radiation is one of the central effects in relativistic electrodynamics, which lends its name to a vast class of optical phenomena in which a moving source emits off-axis radiation, giving rise to a signature Cherenkov emission cone. When a radiation source is confined to a finite path, however, translational symmetry of its motion is removed, giving rise to edge effects that modify the canonical picture of conical emission. Here, we focus on one class of such edge effects as the key to understanding the properties of secondary radiation by laser-induced filaments. Charge-current transients near the edges of laser filaments are shown to couple Cherenkov emission to bremsstrahlung and transition radiation, giving rise to filament-length-sensitive features in the radiation field structure. We present a unified description of this class of radiation phenomena with a continuous analytical crossover from the subluminal to the superluminal setting of radiating currents and with the low-frequency cutoff in the radiation spectrum defined by the filament length.

We find that stimulated Raman excitation of an atom by a two-photon pulse can be enhanced by orders of magnitude if the photons are simultaneously frequency correlated and spatially anticorrelated. That is, a correlated photon pair must have an inherent time delay between its constituent photons. This counterintuitive feature is a manifestation of the uncertainty principle, which yields that frequency-correlated photons cannot be time (spatially) correlated. This is opposite to two-photon absorption by a three-level atom, for which the enhancement occurs if photons in the pulse are frequency anticorrelated and spatially correlated, that is, photons in the pair simultaneously interact with the atom. Our findings can be useful for imaging and spectroscopy of biological samples which demand low illumination intensity.

Vectorial four-wave mixing of low-power ultrashort laser pulses in a highly nonlinear fiber with a properly optimized dispersion profile is shown to enable an efficient generation of high-quality photon pairs with photon-pair count rates above 10 6 pairs/(s mW). A superbunching regime of photon-pair generation with the correlation coefficients g ( 2 ) ( 0 ) exceeding 1200 is demonstrated with pump powers p as low as 0.1 mW. Very low values of heralded-photon correlation coefficients, g c 2 0 3 ⋅ 1 0 − 3 , achieved in the low-p regime reveal a strong antibunching in the signal-photon channel, indicating that more than 99.7% of the signal counts correspond to truly single-photon states.

A harmonically driven cavity QED system consisting of two cavities and a two-level qubit is shown to enable the generation of a vast class of maximally entangled states suitable for measurements with a Heisenberg-limit precision. As one of its modalities, this system can serve as a quantum beam splitter, converting an |N〉 ⊗ |0〉 input into a maximally entangled N00N state (|N〉 ⊗ |0〉 + |0〉 ⊗ |N〉)/$$\sqrt{{\bf{2}}}$$2 at its output. A network of such quantum beam splitters is shown to provide a source of multimode N00N-type entanglement.

Accurate, high spatial resolution thermal measurements have provided fundamental insights into many fields of study; however, existing thermometer technology often suffers from one or more limitati...

The retrosplenial cortex (RSC) plays a key role in spatial navigation and contextual encoding. It was also shown that RSC is activated in presence of landmark-like objects and during object recognition task. However, the essence of RSC activity during place and object exploration remains unclear. Here we utilized the optic-fiber photometry calcium imaging to record the RSC activity during exploratory behavior in novel object and novel place recognition tasks in mice. We showed that object exploration led to decrease in RSC calcium activity independently of behavioral task. Moreover, another form of exploratory behavior - rearing, was now accompanied by such decrease in RSC activity. Altogether, we showed the specific change in RSC activation during object exploration in mice.

We report an observation of the linear Stark effect in a ${\mathrm{Tm}}^{3+}:{\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$ crystal with the distribution of the Stark coefficient over the ion ensemble. We associate this effect with local lattice distortions near the positions of ${\mathrm{Tm}}^{3+}$ ions. Using this effect, the addressable storage of a series of weak light pulses in a cavity-assisted scheme of the revival of silenced echo quantum memory protocol is implemented. In this memory scheme, we also demonstrate storage of a light pulse on the few photon level. The application of an optical resonator makes it possible to increase the memory efficiency in this crystal and to reduce the minimal number of photons in the input signal pulse to 5.6 for the signal-to-noise ratio of 1 in the retrieved echo pulse. The results are in good agreement with the theoretical analysis. The possible ways of the further improvement of the implemented memory scheme are also discussed.

With the wavelength of a short-pulse laser driver shifted to the midinfrared range, the low-frequency output of laser-induced plasmas can be drastically enhanced, as our experiments show, providing a source of ultrabroadband radiation with a spectrum spanning across the entire terahertz, millimeter-wave, and microwave bands. At low gas pressures, such ultrabroadband field waveforms are shown to rapidly build up their coherence, developing a well-resolved emission cone, dominated by a radial radiation energy flux. As counterintuitive as it may seem, this behavior of the intensity, coherence, and polarization of the low-frequency plasma output is shown to be consistent with a physical scenario of Cherenkov-type radiation emission by ponderomotively driven plasma currents.