We present an experimental study of temperature-dependent near-infrared fluorescence spectra of nickel color centers in diamond. The amplitude, the central wavelength, and the linewidth of the zero-phonon line (ZPL) in the fluorescence spectrum of these centers exhibit a strong temperature dependence, enabling highly sensitive temperature measurements. Due to the ZPL wavelength, falling within the biological transparency window, combined with a high-temperature sensitivity and low noise floor, as demonstrated by our experiments in practical thermometry settings, nickel color centers in diamond are ideally suited for all-optical temperature measurements, including thermometry of biological systems.

Thermogenetics is a promising neuromodulation technique based on the use of heat-sensitive ion channels. However, on the way to its clinical application, a number of questions have to be addressed. First, to avoid immune response in future human applications, human ion channels should be studied as thermogenetic actuators. Second, heating levels necessary to activate these channels in vivo in brain tissue should be studied and cytotoxicity of these temperatures addressed. Third, the possibility and safety of chronic neuromodulation has to be demonstrated. In this study, we present a comprehensive framework for thermogenetic neuromodulation in vivo using the thermosensitive human ion channel hTRPV1. By targeting hTRPV1 expression to excitatory neurons of the mouse brain and activating them within a non-harmful temperature range with a fiber-coupled infrared laser, we not only induced neuronal firing and stimulated locomotion in mice, but also demonstrated that thermogenetics can be employed for repeated neuromodulation without causing evident brain tissue injury. Our results lay the foundation for the use of thermogenetic neuromodulation in brain research and therapy of neuropathologies.

All-optical thermometry based on laser-driven photoluminescence (PL) of germanium–vacancy (GeV−) centers in diamond is quantified in terms of a trade-off between temperature sensitivity and laser-induced heating. We show that the noise-floor sensitivity ηT of the temperature readout from the GeV− PL return scales as (pΔt)−1/2 with the laser power p and detection time Δt, allowing the temperature uncertainty to be reduced by increasing p and Δt. This noise-floor reduction is, however, never penalty-free. Specifically, higher laser powers translate into higher temperatures of the diamond crystal. We demonstrate that the noise-floor as low as ηT = 37.5 mK/Hz can be achieved with the laser power set at p = 6.30 mW. We also show that a further reduction of ηT is possible at higher p. The experimental setting implemented in this study helps keep the level of heat released in a diamond crystal well below the typical level of microwave-induced heating in nitrogen-vacancy center-based thermometry, thus offering an advantageous approach for diamond-based thermometry in biological systems.

Canonical nonlinear optics treats self-focusing as a deterministic beam evolution scenario, unfolding above the self-focusing threshold due to the intensity-dependent change in the refractive index. While this deterministic view is adequate for a vast class of nonlinear processes, its insight into stochastic nonlinear phenomena, including laser-induced damage and self-focusing-enhanced spectral transformations, is limited. Here, we present a stochastic treatment of self-focusing. We derive a closed-form analytical solution for the count rate of extreme self-focusing events in nonlinear beam dynamics below the self-focusing threshold. We show that the rare-event statistics of subthreshold self-focusing is highly sensitive to the signal-to-noise ratio and the bandwidth of the laser field waveform. For low-signal-to-noise beams, the rare-event distribution of deeply subthreshold self-focusing is shown to exhibit a manifestly nonexponential tail, thus indicating the enhancement of extreme self-focusing events. We show that subthreshold self-focusing is further enhanced by a broader bandwidth of the noise component of the laser field. It is such broadband, low-signal-to-noise laser fields that are especially prone to deeply subthreshold, rogue-wave self-focusing, lowering, via a laser-induced breakdown, the lifetime of downstream optics.

Unlike the deterministic theory of modulation instability (MI), which describes this process in terms of a well-defined gain spectrum and a well-resolved threshold, the statistical treatment of MIs, presented in this study, is concerned with a question as to how probable MI-driven beam-instability events are. We show that stochastic laser beams that nominally meet the deterministic beam-stability criterion can emerge as unstable on large pulse samples. With the laser peak power set well below the deterministic MI threshold, the count rate of MI-driven beam-instability events within a large sample of laser pulses is shown to be Poissonian-distributed, with its mean defined by the exponent of the extreme-event beam-instability statistics. We present a closed-form analytical solution for this beam-instability count rate, revealing the key tendencies in its behavior as a function of the signal-to-noise ratio and the bandwidth of its noise component. We demonstrate that the stochastic beam-instability dynamics of high-power laser field waveforms, including the laser pulses used for the ignition of inertial confinement fusion, can be scaled down in laser power and studied in laboratory-scale laser experiments.

We present a novel approach for Stimulated Raman Scattering (SRS) spectroscopy in which a hyper spectral resolution and high-speed spectral acquisition are achieved by employing amplified offset-phase controlled fs-pulse bursts. We investigate the method by solving the coupled non-linear Schrödinger equations and validate it by numerically characterizing SRS in molecular nitrogen as a model compound. The spectral resolution of the method is found to be determined by the inverse product of the number of pulses in the burst and the intraburst pulse separation. The SRS spectrum is obtained through a motion-free scanning of the offset phase that results in a sweep of the Raman-shift frequency. Due to high spectral resolution and fast motion-free scanning the technique is beneficial for a number SRS-based applications such as gas sensing and chemical analysis.

Devices based on photonic integrated circuits play a crucial role in the development of low-cost, high-performance, industry-scale manufacturable sensors. We report the design, fabrication, and application of a silicon nitride waveguide-based integrated photonic sensor in Young's interferometer configuration combined with Complementary Metal-Oxide-Semiconductor (CMOS) imaging detection. We use a finite-difference time-domain method to analyze the performance of the sensor device and optimize the sensitivity of the fundamental transverse-electric (TE) mode. We develop a low-cost fabrication method for the photonic sensor chip, using photolithography-compatible dimensions, and produce the sensing region with wet-etching of silicon dioxide. We demonstrate the sensor's functioning by measuring the optical phase shift with glucose concentration in an aqueous solution. We obtain consistent interference patterns with fringe visibility exceeding 0.75 and measure the phase differences for glucose concentrations in the 10 ug/ml order, corresponding to the order of 10^7 molecules in the sensing volume. We envision extending this work to functionalized surface sensors based on molecular binding. Our work will impact biosensing applications and, more generally, the fabrication of interferometric-based photonic devices.

Analysis of extreme-value statistics of stochastic laser pulses suggests a closed-form, quantitative criterion of self-focusing avoidance. We present an analytical solution for the excess kurtosis of the statistics of nonlinear-optical processes, which is shown to be a rapidly growing function of the nonlinearity order, thus indicating a physically significant redistribution of statistical weight within the probability distribution of the respective nonlinear readouts from its central part to its tails. Unlike deterministic self-focusing, whose criterion is expressed in terms of a well-defined self-focusing threshold P-cr, its stochastic counterpart is a probabilistic process whose combined probability for a sample of N laser pulses builds up as a function of N, leading to N-dependent self-focusing avoidance criteria. Specifically, for N>> 1 laser pulses with a signal-to-noise ratio a, the criterion of self-focusing avoidance is shown to shift as a(2)P(cr)/(2 ln N). Instead of dealing with a question as to how to completely avoid self-focusing, stochastic analysis has to deal with a question of how to effectively manage the self-focusing probability over a finite sample of laser shots. The occurrence of self-focusing in stochastic nonlinear optics is thus not a question of i f, but a question of when.

We show that, although nonlinear optics may give rise to a vast multitude of statistics, all these statistics converge, in their extreme-value limit, to one of a few universal extreme-value statistics. Specifically, in the class of polynomial nonlinearities, such as those found in the Kerr effect, weak-field harmonic generation, and multiphoton ionization, the statistics of the nonlinear-optical output converges, in the extreme-value limit, to the exponentially tailed, Gumbel distribution. Exponentially growing nonlinear signals, on the other hand, such as those induced by parametric instabilities and stimulated scattering, are shown to reach their extreme-value limits in the class of the Fréchet statistics, giving rise to extreme-value distributions (EVDs) with heavy, manifestly nonexponential tails, thus favoring extreme-event outcomes and rogue-wave buildup.

The first passage time extended to stochastic nonlinear beam dynamics emerges as a natural time scale and a meaningful estimator for the expected wait time to the first self-focusing event within a large sample of stochastic laser pulses. We show that the ratio P/Pcr of the laser peak power P to the critical power of self-focusing Pcr, which plays a central role in deterministic self-focusing, keeps its status as a key governing parameter in stochastic self-focusing. However, in contrast to its deterministic counterpart, the Pcr/P ratio of a stochastic laser beam is no longer an indicator of whether self-focusing will occur, but is, rather, a predictor of when the self-focusing is expected, in the sense of the first passage time, given the statistics of the laser field.

Statistics of extreme events in optics, defined as above-threshold counts of an optical signal, is shown to converge, in the large-sample-size limit, to a generalized Poisson distribution whose mean is found via the exponent of the respective extreme-value distribution. Specifically, extreme-event readouts from polynomial and exponential optical nonlinearities are shown to converge in their statistics to Poisson distributions whose means are, respectively, exponential and slower-than-exponential functions of the extreme-event-counter threshold. Extreme-event counts of a phase readout, on the other hand, converge to a Poisson process whose mean is a light-tailed function of the threshold. The Poisson-limit property of extreme events in optics suggests a powerful resource for a unified treatment of a vast variety of extreme-event phenomena, ranging from optical rogue waves to laser-induced damage.

Statistics of self-focusing induced by a stochastic laser driver is shown to converge, in the large-sample-size limit, to a generalized Poisson distribution whose mean is given by the exponent of the respective extreme-value statistics. For a given ratio of the laser peak power to the self-focusing threshold P cr , the mean number of self-focusing counts in a large sample of laser pulses is shown to depend on the number of pulses in the sample, N , and the signal-to-noise ratio of laser pulses, a . We derive a closed-form solution for the threshold of stochastic self-focusing, which, unlike its deterministic counterpart, P cr , is a function of the sample size N and the signal-to-noise ratio a . The parameter N a = exp (a2/2) is shown to set a borderline between the deterministic and stochastic regimes of self-focusing. When the number of laser pulses in a sample becomes comparable to N a , self- focusing can no longer be viewed as deterministic even for high signal-to-noise laser beams. (c) 2024 Optica Publishing Group

We examine the spectral broadening of stochastic laser pulses experiencing self-phase modulation (SPM) in a medium with Kerr nonlinearity. The statistics of extreme bandwidths emerging from such a process is shown to converge, in the large-sample-size limit, to a generalized Poisson distribution whose mean is given by the exponent of the respective extreme-event statistics. In striking contrast to the SPM spectral broadening of deterministic laser pulses, the properties of spectral broadening in stochastic SPM depend not only on the field intensity and the propagation path, but also on the signal-to-noise ratio a of laser pulses and the sample size N. For N >> 1 laser pulses with a high signal-to-noise ratio, the upper bound of SPM-broadened spectra shifts as (lnN/a(2))delta(s), delta(s) being the deterministic SPM bandwidth. The parameter N-a = exp(a(2)/2) is shown to provide an important benchmark, setting a borderline between deterministic and stochastic SPM. These findings offer useful insights into the extreme-event properties of supercontinuum generation.

It is shown experimentally that the intensities of characteristic X-rays, terahertz radiation, and the second optical harmonic from a copper foil irradiated by sub-relativistic femtosecond laser pulses increase simultaneously with decreasing foil thickness. The efficiency of the generation of X-rays and terahertz radiation, as well as the 3/2 harmonic with a various degree of nonlinearity, depends on the intensity of radiation and the duration of a laser pulse. the behavior of measured signals is determined by the instability of the two-plasmon decay, by hot electrons, and by their circulation in observed processes.

ABSTRACT Virtually all major processes in cells and tissues are regulated by calcium ions (Ca 2+ ). Understanding the influence of Ca 2+ on cell function requires technologies that allow for non-invasive manipulation of intracellular calcium levels including the formation of calcium patterns, ideally in a way that is expandable to intact organisms. The currently existing tools for optical and optogenetic Ca 2+ manipulation are limited with respect to response time, and tissue penetration depth. Here we present G enetically E ncoded C alcium Co ntroller ( GECCO ), a system for thermogenetic Ca 2+ manipulation based on snake TRP channels optically controlled by infrared illumination. GECCO is functional in animal and plant cells and allows studying how cells decode different profiles of Ca 2+ signals. GECCO enabled the shaping of insulin release from β-cells, the identification of drugs that potentiate Ca 2+ -induced insulin release, and the generation of synthetic Ca 2+ signatures in plants.

With a notable exception of space–time variable swap, pulse evolution equations of ultrafast optics are mathematically similar to the equations of quantum mechanics and beam dynamics. The Lagrangian structure of these equations is, however, much less intuitive. Here, we show that such a structure can be identified via a path-integral analysis of the pulse evolution equation, offering useful insights into the Lagrangian underpinning of ultrafast nonlinear optics. The Euler–Lagrange equation applied to the optical analog of the Lagrange function leads to a second-order differential equation that parallels in its structure second Newton's law. Stationary-phase space–time paths found by solving such an equation reveal the hidden inner workings behind a vast class of field-waveform transformations in ultrafast optics, including the buildup of nonlinear phase, modulation instabilities, and soliton breather dynamics.

We examine the spatial modulation instability (MI) of a partially incoherent laser beam. We show that the P < (a/rc)2P0 criterion of beam stability, with a laser peak power P, beam radius a, correlation radius rc, and critical power of self-focusing P0, is applicable only to a limited class of MIs, viz., MIs that can be described as instabilities of a pertinent transverse correlation function found as a solution to the evolution equation, where the expectation of the four-field-product nonlinear source term is factorized as a product of the field intensity and a two-point transverse correlation function. When extended to a more general class of MIs, field evolution analysis of partially coherent beams suggests that MIs can be attenuated, but never completely suppressed. We show that spatial incoherence can lower the MI-buildup rate, thus helping avoid MI-induced beam breakup in physical settings where the MI-buildup length lMI can be kept longer than the length of the nonlinear medium L. Because the lMI > L condition sets a limitation on the field intensity rather than the laser peak power, MI-induced beam breakup can be avoided, even at laser peak powers well above the critical power of self-focusing P0.

Rapidly progressing laser technologies provide powerful tools to study potential barrier-passage dynamics in physical, chemical, and biological systems with unprecedented temporal and spatial resolution and a remarkable chemical and structural specificity. The available theories of barrier passage, however, operate with equations, potentials, and parameters that are best suited for a specific area of research and a specific class of systems and processes. Making connections among these theories is often anything but easy. Here, we address this problem by presenting a unified framework for the description of a vast variety of classical and quantum barrier-passage phenomena, revealing an innate connection between various types of barrier-passage dynamics and providing closed-form equations showing how the signature exponentials in classical and quantum barrier-passage rates relate to and translate into each other. In this framework, the Arrhenius-law kinetics, the emergence of the Gibbs distribution, Hund's molecular wave-packet well-to-well oscillatory dynamics, Keldysh photoionization, and Kramers' escape over a potential barrier are all understood as manifestations of a potential-driven Markovian dynamics whereby a system evolves from a state of local stability. Key to the irreducibility of quantum tunneling to thermally activated barrier passage is the difference in the ways the diffusion-driving potentials emerge in these two tunneling settings, giving rise to stationary states with a distinctly different structure.

Diabetes is one of the significant risk factors for ischemic stroke. Hyperglycemia exacerbates the pathogenesis of stroke, leading to more extensive cerebral damage and, as a result, to more severe consequences. However, the mechanism whereby the hyperglycemic status in diabetes affects biochemical processes during the development of ischemic injury is still not fully understood. In the present work, we record for the first time the real-time dynamics of H2O2 in the matrix of neuronal mitochondria in vitro in culture and in vivo in the brain tissues of rats during development of ischemic stroke under conditions of hyperglycemia and normal glucose levels. To accomplish this, we used a highly sensitive HyPer7 biosensor and a fiber-optic interface technology. We demonstrated that a high glycemic status does not affect the generation of H2O2 in the tissues of the ischemic core, while significantly exacerbating the consequences of pathogenesis. For the first time using Raman micro-spectroscopy approach, we have shown how a sharp increase in the blood glucose level increases the relative amount of reduced cytochromes in the mitochondrial electron transport chain in neurons under normal conditions in awake mice.

The notion of the first passage time is shown to offer a meaningful extension to quantum tunneling, providing a closed-integral-form analytical unification of the tunneling rate and the tunneling passage time. We demonstrate that, in suitable potential settings, the quantum first passage time, found as a solution to the Fokker-Planck and backward Kolmogorov's equations for the quantum probability density, recovers the hallmark results for the Kramers escape rate, the lifetime of tunneling quasi-stationary wave packets, leads to a classical, distance-over-speed passage time for a free-particle wave function, and offers useful insights into Keldysh's intimation on the electron barrier-traversal time in field-induced ionization.