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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.

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

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

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.

Ischemic cerebral stroke is one of the leading causes of death and disability in humans. However, molecular processes underlying the development of this pathology remain poorly understood. There are major gaps in our understanding of metabolic changes that occur in the brain tissue during the early stages of ischemia and reperfusion. In particular, it is generally accepted that both ischemia (I) and reperfusion (R) generate reactive oxygen species (ROS) that cause oxidative stress which is one of the main drivers of the pathology, although ROS generation during I/R was never demonstrated in vivo due to the lack of suitable methods. In the present study, we record for the first time the dynamics of intracellular pH and H2O2 during I/R in cultured neurons and during experimental stroke in rats using the latest generation of genetically encoded biosensors SypHer3s and HyPer7. We detect a buildup of powerful acidosis in the brain tissue that overlaps with the ischemic core from the first seconds of pathogenesis. At the same time, no significant H2O2 generation was found in the acute phase of ischemia/reperfusion. HyPer7 oxidation in the brain was detected only 24 h later. Comparison of in vivo experiments with studies on cultured neurons under I/R demonstrates that the dynamics of metabolic processes in these models significantly differ, suggesting that a cell culture is a poor predictor of metabolic events in vivo., Highlights • The dynamics of stroke-induced changes in intracellular pH and H2O2 was recorded. • Ischemia leads to immediate acidification of the affected part of the brain. • Only slight increase in H2O2 in the brain tissue occurs during ischemia/reperfusion. • The pronounced increase in H2O2 in the brain occurs next day after I/R. • Neurons show different I/R-induced pH and H2O2 dynamics in vitro and in vivo.

Ultrashort high-energy pulses at wavelengths longer than 1 µm are now desirable for a vast variety of applications in ultrafast and strong-field physics. To date, the main answer to the wavelength tunability for energetic, broadband pulses still relies on optical parametric amplification (OPA), which often requires multiple and complex stages, may feature imperfect beam quality, and has limited conversion efficiency into one of the amplified waves. In this work, we present a completely different strategy to realize an energy-efficient and scalable laser frequency shifter. This relies on the continuous red shift provided by stimulated Raman scattering (SRS) over a long propagation distance in nitrogen-filled hollow-core fibers (HCF). We show a continuous tunability of the laser wavelength from 1030 nm up to 1730 nm with a conversion efficiency higher than 70% and high beam quality. The highly asymmetric spectral broadening, arising from the spatiotemporal nonlinear interplay between higher-order modes of the HCF, can be readily employed to generate pulses ( ∼ 20 f s ) significantly shorter than the pump ones ( ∼ 200 f s ) with high beam quality, and the pulse energy can further be scaled up to tens of millijoules. We envision that this technique, coupled with the emerging high-power Yb laser technology, has the potential to answer the increasing demand for energetic multi-TW few-cycle sources tunable in the near-IR.

Remarkable advancements in the ability to create, manipulate, and measure quantum systems are paving the way to build next generations of devices based on quantum physics. Quantum technologies in Russia are on the list of strategically important cross-cutting directions in the framework of the National Technology Initiative programs and the Digital Economy National Program. The broad focus includes quantum computing and simulation, quantum communications, quantum metrology and sensing. This paper reviews existing research on quantum science and technologies in Russia and summarizes the main goals for the next few years that form the basis of an upcoming major national initiative.

All-optical thermometry presents a promising avenue of investigation for sensitive biological and electronic systems, with methods free of radio-frequency interference of particular importance. In this work, an all-optical scanning fiber thermometer is tested and shown to possess $5\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{m}$ spatial and $20\phantom{\rule{0.2em}{0ex}}\mathrm{mK}/\sqrt{\mathrm{Hz}}$ temperature resolution. This probe is then used to generate noncontact scanning thermal images of active circuit elements with microscale thermal features.

The signal-to-noise contrast of the optical readout in broadband Raman quantum memories is analyzed as a function of the pulse widths and phase properties of tailored optical field waveforms used to write in and read out broadband photon wave packets. Based on this analysis, we quantify the tradeoff between the readout contrast and the speed of such memories. Off-resonance coherent four-wave mixing is shown to provide a source of noise photons, lowering the readout contrast in broadband Raman quantum memories. This noise cannot be suppressed by phase matching, but can be radically reduced with a suitable polarization arrangement and proper field-waveform tailoring.

We perform a detailed theoretical and experimental investigation of supercontinuum generation in large-mode-area photonic crystal fibers pumped by a high-energy, high-repetition rate picosecond Nd:YVO4 laser, with the goal of using it as the Stokes beam in coherent anti-Stokes Raman scattering setup. We analyze the influence of fiber structure and length on the supercontinuum power, spectral shape, and group delay dispersion. We identify the experimental conditions for stable supercontinuum generation, with microjoule-level pulse energy and the spectrum extending beyond 1600 nm, which allows excitation of Raman frequencies up to 3000 cm−1 and beyond. We demonstrate reliable and efficient operation of a coherent anti-Stokes Raman spectroscopy and microscopy setup using this supercontinuum source.

Thermogenetics is a promising innovative neurostimulation technique, which enables robust activation of neurons using thermosensitive transient receptor potential (TRP) cation channels. Broader application of this approach in neuroscience is, however, hindered by a limited variety of suitable ion channels, and by low spatial and temporal resolution of neuronal activation when TRP channels are activated by ambient temperature variations or chemical agonists. Here, we demonstrate rapid, robust and reproducible repeated activation of snake TRPA1 channels heterologously expressed in non-neuronal cells, mouse neurons and zebrafish neurons in vivo by infrared (IR) laser radiation. A fibre-optic probe that integrates a nitrogen−vacancy (NV) diamond quantum sensor with optical and microwave waveguide delivery enables thermometry with single-cell resolution, allowing neurons to be activated by exceptionally mild heating, thus preventing the damaging effects of excessive heat. The neuronal responses to the activation by IR laser radiation are fully characterized using Ca2+ imaging and electrophysiology, providing, for the first time, a complete framework for a thermogenetic manipulation of individual neurons using IR light., Current approaches to thermogenetic manipulation of neuronal activity lack sufficient spatiotemporal resolution. Here the authors show that neurons expressing snake TRPA1 channels are activated at high temporal resolution with IR light and this technique can be used to elicit behaviour in zebrafish larvae.

We present experimental studies of long-distance transmission of ultrashort mid-infrared laser pulses through atmospheric air, probing air dispersion in the 3.6–4.2-μm wavelength range. Atmospheric air is still highly transparent to electromagnetic radiation in this spectral region, making it interesting for long-distance signal transmission. However, unlike most of the high-transmission regions in gas media, the group-velocity dispersion, as we show in this work, is anomalous at these wavelengths due to the nearby asymmetric-stretch rovibrational band of atmospheric carbon dioxide. The spectrograms of ultrashort mid-infrared laser pulses transmitted over a distance of 60 m in our experiments provide a map of air dispersion in this wavelength range, revealing clear signatures of anomalous dispersion, with anomalous group delays as long as 1.8 ps detected across the bandwidth covered by 80-fs laser pulses.

Phase matching is shown to provide a tunable gate that helps discriminate entangled states of light generated by four-wave mixing (FWM) in optical fibers against uncorrelated photons originating from Raman scattering. Two types of such gates are discussed. Phase-matching gates of the first type are possible in the normal dispersion regime, where FWM sidebands can be widely tuned by high-order dispersion management, enhancing the ratio of the entangled-photon output to the Raman noise. The photon-entanglement gates of the second type are created by dual-pump cross-phase-modulation-induced FWM sideband generation and can be tuned by group-velocity mismatch of the pump fields.

Compression of optical pulses to ultrashort pulse widths using methods of nonlinear optics is a well-established technology of modern laser science. Extending these methods to pulses with high peak powers, which become available due to the rapid progress of laser technologies, is, however, limited by the universal physical principles. With the ratio P/Pcr of the peak power of an ultrashort laser pulse, P, to the critical power of self-focusing, Pcr, playing the role of the fundamental number-of-particles integral of motion of the nonlinear Schrödinger equation, keeping this ratio constant is a key principle for the power scaling of laser-induced filamentation. Here, we show, however, that, despite all the complexity of the underlying nonlinear physics, filamentation-assisted self-compression of ultrashort laser pulses in the regime of anomalous dispersion can be scaled within a broad range of peak powers against the principle of constant P/Pcr. We identify filamentation self-compression scaling strategies whereby subcycle field waveforms with almost constant pulse widths can be generated without a dramatic degradation of beam quality within a broad range of peak powers, varying from just a few to hundreds of Pcr.

We perform a proof-of-principle demonstration of chemically specific standoff gas sensing, in which a coherent stimulated Raman signal is detected in the direction anticollinear to a two-color laser excitation beam traversing the target volume. The proposed geometry is intrinsically free space as it does not involve back-scattering (reflection) of the signal or excitation beams at or behind the target. A beam carrying an intense mid-IR femtosecond (fs) pulse and a parametrically generated picosecond (ps) UV Stokes pulse is fired in the forward direction. A fs filament, produced by the intense mid-IR pulse, emits a backward-propagating narrowband ps laser pulse at the 337 and 357 nm transitions of excited molecular nitrogen, thus supplying a counter-propagating Raman pump pulse. The scheme is linearly sensitive to species concentration and provides both transverse and longitudinal spatial resolution.

The electron spin of nitrogen--vacancy (NV) centers in diamond offers a solid-state quantum bit and enables high-precision magnetic-field sensing on the nanoscale. Implementation of these approaches in a fiber format would offer unique opportunities for a broad range of technologies ranging from quantum information to neuroscience and bioimaging. Here, we demonstrate an ultracompact fiber-optic probe where a diamond microcrystal with a well-defined orientation of spin quantization NV axes is attached to the fiber tip, allowing the electron spins of NV centers to be manipulated, polarized, and read out through a fiber-optic waveguide integrated with a two-wire microwave transmission line. The microwave field transmitted through this line is used to manipulate the orientation of electron spins in NV centers through the electron-spin resonance tuned by an external magnetic field. The electron spin is then optically initialized and read out, with the initializing laser radiation and the photoluminescence spin-readout return from NV centers delivered by the same optical fiber.

Seeing the big picture of functional responses within large neural networks in a freely functioning brain is crucial for understanding the cellular mechanisms behind the higher nervous activity, including the most complex brain functions, such as cognition and memory. As a breakthrough toward meeting this challenge, implantable fiber-optic interfaces integrating advanced optogenetic technologies and cutting-edge fiber-optic solutions have been demonstrated, enabling a long-term optogenetic manipulation of neural circuits in freely moving mice. Here, we show that a specifically designed implantable fiber-optic interface provides a powerful tool for parallel long-term optical interrogation of distinctly separate, functionally different sites in the brain of freely moving mice. This interface allows the same groups of neurons lying deeply in the brain of a freely behaving mouse to be reproducibly accessed and optically interrogated over many weeks, providing a long-term dynamic detection of genome activity in response to a broad variety of pharmacological and physiological stimuli.

Phase-stable half-cycle mid-infrared pulses were produced through filamen- tation in argon. The pulse width was obtained as 7.9 fs at 4.1 m carrier wavelength by using frequency-resolved optical gating.

We have studied coherent emission from ambient air and demonstrated efficient generation of laser-like beams directed both forward and backward with respect to a nanosecond ultraviolet pumping laser beam. The generated optical gain is a result of two-photon photolysis of atmospheric O 2 , followed by two-photon excitation of atomic oxygen. We have analyzed the temporal shapes of the emitted pulses and have observed very short duration intensity spikes as well as a large Rabi frequency that corresponds to the emitted field. Our results suggest that the emission process exhibits nonadiabatic atomic coherence, which is similar in nature to Dicke superradiance where atomic coherence is large and can be contrasted with ordinary lasing where atomic coherence is negligible. This atomic coherence in oxygen adds insight to the optical emission physics and holds promise for remote sensing techniques employing nonlinear spectroscopy.

We report the first (to our knowledge) experimental results and numerical simulations on mid-IR femtosecond pulse filamentation in argon using 0.1 TW peak-power, 80 fs, 3.9 μm pulses. A broadband supercontinuum spanning the spectral range from 350 nm to 5 μm is generated, whereby about 4% of the mid-IR pulse energy is converted into the 350-1700 nm spectral region. These mid-IR-visible coherent continua offer a new, unique tool for time-resolved spectroscopy based on a mid-IR filamentation laser source.

Ultralow-power diode-laser radiation is employed to induce photodesorption of cesium from a partially transparent thin-film cesium adsorbate on a solid surface. Using resonant Raman spectroscopy, we demonstrate that this photodesorption process enables an accurate local optical control of the density of dimer molecules in alkali-metal vapors., 4 pages, 4 figures

This paper presents a fully experimental and theoretical study on transmission properties of a deep metallic grating with subwavelength slits in THz frequency region by using THz time domain spectroscopy (THz-TDS). The grating exposed top-polarized incident wave exhibits enhanced nonresonant transmission in the long-wavelength region where the incident wavelength is larger than the grating period. Wood anomalies are observed when the wavelength is comparable to the grating period. Strict theory is given to explain the experimental results and the two are in good agreement. It is proposed that the Wood dips may be considered a criterion and a tool to judge and control the uniformity or fabricating accuracy of the grating period.

Conventional and scanning near-field optical microscopy techniques are cross referenced to femtosecond nonlinear-optical measurements and finite-element numerical simulations to visualize and analyze a strong confinement of electromagnetic radiation in guided modes of a photonic-crystal fiber with only a few air holes surrounding the fiber core. A nonlinear coefficient of about 120 W−1 km−1 is achieved at the wavelength of 670 nm for a fused-silica fiber with a full hexagonal cycle of closely packed air holes around the fiber core. The removal of a single element from this array of air holes is shown to frustrate field confinement in guided modes, leading to mode leakage.

Second- and third-harmonic generation in silicon carbide (SiC) nanopowders embedded in a polymethyl methacrylate (PMMA) film are studied using nano-, pico-, and femtosecond laser pulses. Second- and third-harmonic generation processes are shown to allow the detection of absorptive agglomerates of nanocrystals in transparent materials and the visualization of optical breakdown in nanocomposite materials. Polarization of the third-harmonic signal is shown to be highly sensitive to the polarization of the pump field, permitting third-harmonic generation to be used as a probe for the anisotropy of nanocomposite materials. The second-harmonic signal, on the contrary, has no memory of the initial polarization state of the pump field and is, consequently, ideally suited as a measure of orientation-averaged nonlinearities of nanopowder materials.

Polarization properties of the second and third harmonics generated by 75 fs pulses of a Cr:forsterite laser in polymer films doped with SiC nanopowders are studied. The processes of second- and third-harmonic generation in such films originate from different nonlinear sources, giving rise to harmonic signals with different polarizations. The second harmonic, produced in randomly oriented anisotropic noncentrosymmetric SiC nanocrystals, is shown to be totally depolarized. By contrast, the third harmonic, mainly generated in the isotropic polymer material, is preferentially polarized along the polarization vector of the pump field.