In-situ nonvolatile and volatile modulation for optical neural networks

High-performance integrated optical memristors are crucial in developing optical neural networks based on in-memory computing.Such devices are building blocks capable of modulating the transmission of a propagating mode in a multilevel and nonvolatile fashion,thus allowing storage and multiplication of analog signals in the same device.1 Chalcogenide phase change materials(PCMs)are candidates for high-performance devices.

Universal frequency engineering tool for microcavity nonlinear optics:multiple selective mode splitting of whispering-gallery resonances

Whispering-gallery microcavities have been used to realize a variety of efficient parametric nonlinear optical processes through the enhanced light–matter interaction brought about by supporting multiple high quality factor and small modal volume resonances.Critical to such studies is the ability to control the relative frequencies of the cavity modes,so that frequency matching is achieved to satisfy energy conservation.Typically this is done by tailoring the resonator cross section.Doing so modifies the frequencies of all of the cavity modes,that is,the global dispersion profile,which may be undesired,for example,in introducing competing nonlinear processes.Here,we demonstrate a frequency engineering tool,termed multiple selective mode splitting(MSMS),that is independent of the global dispersion and instead allows targeted and independent control of the frequencies of multiple cavity modes.In particular,we show controllable frequency shifts up to 0.8 nm,independent control of the splitting of up to five cavity modes with optical quality factors≳10^5,and strongly suppressed frequency shifts for untargeted modes.The MSMS technique can be broadly applied to a wide variety of nonlinear optical processes across different material platforms and can be used to both selectively enhance processes of interest and suppress competing unwanted processes.

Overcoming thermo-optical dynamics in broadband nanophotonic sensing

Advances in integrated photonics open up exciting opportunities for batch-fabricated optical sensors using high-quality-factor nanophotonic cavities to achieve ultrahigh sensitivities and bandwidths.The sensitivity improves with increasing optical power;however,localized absorption and heating within a micrometer-scale mode volume prominently distorts the cavity resonances and strongly couples the sensor response to thermal dynamics,limiting the sensitivity and hindering the measurement of broadband time-dependent signals.Here,we derive a frequency-dependent photonic sensor transfer function that accounts for thermo-optical dynamics and quantitatively describes the measured broadband optomechanical signal from an integrated photonic atomic force microscopy nanomechanical probe.Using this transfer function,the probe can be operated in the high optical power,strongly thermo-optically nonlinear regime,accurately measuring low-and intermediate-frequency components of a dynamic signal while reaching a sensitivity of 0.7fm/Hz^(1/2) at high frequencies,an improvement of=10x relative to the best performance in the linear regime.Counterintuitively,we discover that a higher transduction gain and sensitivity are achieved with lower quality-factor optical modes for low signal frequencies.Not limited to optomechanical transducers,the derived transfer function is generally valid for describing the small-signal dynamic responses of a broad range of technologically important photonic sensors subject to the thermo-optical effect.

Optical haze of transparent and conductive silver nanowire films

当代的 nanostructured 为在太阳能电池的使用的透明电极要求高发射度和高电导率，与高方面比率支配 nanostructures。光薄雾是在为被 nanostructures 的几何学也决定的太阳能电池的透明电极的一个同等地重要的还未学得的参数填写电极。在这个工作，在可见光谱的光薄雾价值上的银 nanowire 直径的效果用与小直径(60 nm ) 或大直径(150 nm ) 由电线组成的电影被调查。有限差别时间领域(FDTD ) 模拟和试验性的发射度数据证实更高根据优点的当前的数字的意见执行透明进行的电极(TCE ) 电影的那种更小的直径 nanowires 形式。当为每部电影在经常的发射度和电导率附近维持时，然而，电影与更大的直径银 nanowires 创作了，这试验性地被观察与更小的直径比电影有一个更高的薄雾因素。这与同样大、小的直径为单个 nanowires 证实薄雾因素的 FDTD 模拟。这是为被模仿了或试验性地测量了的 Ag NW 的薄雾性质的第一个记录，并且也，第一证实为 TCE 的优点的当前的数字是不够的在太阳能电池设备评估他们的表演。

Nanoscale chemical imaging of individual chemotherapeutic cytarabineloaded liposomal nanocarriers

Dosage of chemotherapeutic drugs is a tradeoff between efficacy and side-effects.Liposomes are nanocarriers that increase therapy efficacy and minimize side-effects by delivering otherwise difficult to administer therapeutics with improved efficiency and selectivity.Still,variabilities in liposome preparation require assessing drug encapsulation efficiency at the single liposome level,an information that,for non-fluorescent therapeutic cargos,is inaccessible due to the minute drug load per liposome.Photothermal induced resonance (PTIR) provides nanoscale compositional specificity,up to now,by leveraging an atomic force microscope (AFM) tip contacting the sample to transduce the sample's photothermal expansion.However,on soft samples (e.g.,liposomes) PTIR effectiveness is reduced due to the likelihood of tip-induced sample damage and inefficient AFM transduction.Here,individual liposomes loaded with the chemotherapeutic drug cytarabine are deposited intact from suspension via nano-electrospray gas-phase electrophoretic mobility molecular analysis (nES-GEMMA) collection and characterized at the nanoscale with the chemically-sensitive PTIR method.A new tapping-mode PTIR imaging paradigm based on heterodyne detection is shown to be better adapted to measure soft samples,yielding cytarabine distribution in individual liposomes and enabling classification of empty and drug-loaded liposomes.The measurements highlight PTIR capability to detect ~ 103 cytarabine molecules (~ 1.7 zmol) label-free and non-destructively.

Reconstructing phase diagrams from local measurements via Gaussian processes:mapping the temperature-composition space toconfidence

We show the ability to map the phase diagram of a relaxor-ferroelectric system as a function of temperature and composition through local hysteresis curve acquisition,with the voltage spectroscopy data being used as a proxy for the(unknown)microscopic state or thermodynamic parameters of materials.Given the discrete nature of the measurement points,we use Gaussian processes to reconstruct hysteresis loops in temperature and voltage space,and compare the results with the raw data and bulk dielectric spectroscopy measurements.The results indicate that the surface transition temperature is similar for all but one composition with respect to the bulk.Through clustering algorithms,we recreate the main features of the bulk diagram,and provide statistical confidence estimates for the reconstructed phase transition temperatures.We validate the method by using Gaussian processes to predict hysteresis loops for a given temperature for a composition unseen by the algorithm,and compare with measurements.These techniques can be used to map phase diagrams from functional materials in an automated fashion,and provide a method for uncertainty quantification and model selection.

Multi-millijoule terahertz emission from laser- wakefield-accelerated electrons

High-power terahertz radiation was observed to be emitted from a gas jet irradiated by 100-terawatt-class laser pulses in the laser-wakefield acceleration of electrons.The emitted terahertz radiation was characterized in terms of its spectrum,polarization,and energy dependence on the accompanying electron bunch energy and charge under various gas target conditions.With a nitrogen target,more than 4 mJ of energy Was produced at<10 THz with a laser-to-terahertz conversion efficiency of~0.15%.Such strong terahertz radiation is hypothesized to be produced from plasma electrons accelerated by the ponderomotive force of the laser and the plasma wakefelds on the time scale of the laser pulse duration and plasma period.This model is examined with analytic calculations and particle-in-cell simulations to better understand the generation mechanism of high-energy terahertz radiation in laser-wakefield acceleration.

Ionizing terahertz waves with 260 MV/cm from scalable optical rectification

Terahertz(THz)waves,known as non-ionizing radiation owing to their low photon energies,can actually ionize atoms and molecules when a sufficiently large number of THz photons are concentrated in time and space.Here,we demonstrate the generation of ionizing,multicycle,15-THz waves emitted from large-area lithium niobate crystals via phase-matched optical rectification of 150-terawatt laser pulses.A complete characterization of the generated THz waves in energy,pulse duration,and focal spot size shows that the field strength can reach up to 260 megavolts per centimeter.In particular,a single-shot THz interferometer is employed to measure the THz pulse duration and spectrum with complementary numerical simulations.Such intense THz pulses are irradiated onto various solid targets to demonstrate THz-induced tunneling ionization and plasma formation.This study also discusses the potential of nonperturbative THz-driven ionization in gases,which will open up new opportunities,including nonlinear and relativistic THz physics in plasma.

Thermoelectric Properties of p-Type PbSe Nanowires

The thermoelectric properties of individual solution-phase synthesized p-type PbSe nanowires have been examined.The nanowires showed near degenerately doped charge carrier concentrations.Compared to the bulk,the PbSe nanowires exhibited a similar Seebeck coefficient and a significant reduction in thermal conductivity in the temperature range 20 K to 300 K.Thermal annealing of the PbSe nanowires allowed their thermoelectric properties to be controllably tuned by increasing their carrier concentration or hole mobility.After optimal annealing,single PbSe nanowires exhibited a thermoelectric figure of merit(ZT)of 0.12 at room temperature.