Nanosecond Temporal Resolution Research Articles

High-dimensional quantum correlation measurements with an adaptively gated hybrid single-photon camera

Efficient measurement of high-dimensional quantum correlations, especially spatial ones, is essential for quantum technologies. We propose and demonstrate an adaptively gated hybrid intensified camera (HIC) that combines the information from a high spatial resolution sensor and a high temporal resolution detector, offering precise control over the number of photons detected within each frame. The HIC facilitates spatially resolved single-photon counting measurements. We study the measurement of momentum correlations of photon pairs generated in type-I spontaneous parametric downconversion with the HIC and demonstrate the possibility of time-tagging the registered photons. With a spatial resolution of multi-megapixels and nanosecond temporal resolution, this system allows for the realization of previously infeasible quantum optics experiments.

Unraveling the rapid ion migration in perovskite solar cells by circuit-switched transient photoelectric technique.

Ion migration activated by illumination is a critical factor responsible for the performance decline and stability degradation of perovskite solar cells (PSCs). While ion migration has been widely believed to be much slower than charge transport, recent research suggests that, despite the lack of understanding of the mechanism, it may also be involved in a series of rapid photoelectric responses of PSCs. Here, we report an improved circuit-switched transient photoelectric technique with nanosecond temporal resolution, which enables quantitative characterization of ion migration dynamics in PSCs across a fairly broad time window. Specifically, ion migration occurring within microseconds after illumination (corresponding to a diffusion length of ∼10-7cm) is unambiguously identified. In conjunction with the composition engineering protocol, we justify that it arises from the short-range migration of halide anions and organic cations around the contact/perovskite interface. The rapid ion migration kinetics revealed in this work strongly complement the well-established ion migration model, which offers new insights into the mechanism of ion-carrier interaction in PSC devices.

Spatial-temporal characterization of photoemission in a streak-mode dynamic transmission electron microscope.

A long-standing motivation driving high-speed electron microscopy development is to capture phase transformations and material dynamics in real time with high spatial and temporal resolution. Current dynamic transmission electron microscopes (DTEMs) are limited to nanosecond temporal resolution and the ability to capture only a few frames of a transient event. With the motivation to overcome these limitations, we present our progress in developing a streak-mode DTEM (SM-DTEM) and demonstrate the recovery of picosecond images with high frame sequence depth. We first demonstrate that a zero-dimensional (0D) SM-DTEM can provide temporal information on any local region of interest with a 0.37 μm diameter, a 20-GHz sampling rate, and 1200 data points in the recorded trace. We use this method to characterize the temporal profile of the photoemitted electron pulse, finding that it deviates from the incident ultraviolet laser pulse and contains an unexpected peak near its onset. Then, we demonstrate a two-dimensional (2D) SM-DTEM, which uses compressed-sensing-based tomographic imaging to recover a full spatiotemporal photoemission profile over a 1.85-μm-diameter field of view with nanoscale spatial resolution, 370-ps inter-frame interval, and 140-frame sequence depth in a 50-ns time window. Finally, a perspective is given on the instrumental modifications necessary to further develop this promising technique with the goal of decreasing the time to capture a 2D SM-DTEM dataset.

Streamer-induced kinetics of excited states in pure N2: I. Propagation velocity, and vibrational distributions of N2(C) and N(B) states

The emission spectra of a streamer discharge in pure nitrogen provide an important tool for investigating the fundamental kinetics of excited electronic states of N2 and benchmark data for validating advanced kinetic schemes for numerical models. In this work, we characterize a streamer monofilament developed in a dielectric barrier discharge configuration, including electrical characteristics, time-resolved images and N2/N emission spectra, all acquired with nanosecond temporal resolution. Time-resolved images and emission characteristics provide clear evidence of the formation of a cathode-directed streamer and allow determining the streamer propagation velocity and the typical values using the intensity ratio of nitrogen spectral bands in the center of the discharge gap. We also measure the vibrational distributions of the N2(C, 0–4) and N(B, 0–2) states. The population of N2(C, 0–4) state, initially formed by energetic electrons in the streamer head, changes later significantly due to the decrease in the mean energy and concentration of the streamer channel electrons. After a few tens of nanoseconds, the electron-impact excitation rate of N2(C) becomes negligible compared to its population by the N2() + N2() pooling. The experimental findings are supported and consistent with the 0D state-to-state kinetic model results and reveal the participation of high vibrational levels of N2() in the pooling reactions.

Natural sources of intense ultra-high-frequency radiation in high-voltage atmospheric discharges.

We study the sources of intense ultra-high-frequency (UHF) radiation (in the frequency range 1-6GHz) arising during the development of high-voltage atmospheric discharges. The discharges were initiated in a long discharge gap by applying an approximately 1-MV pulse with positive or negative polarity. By employing a radio registration system based on ultrawideband antennas, we managed to localize the UHF radiation sources in the discharge with centimeter accuracy and investigate their temporal and spatial correlation with the discharge structures. The vast majority of the localized sources turned out to be concentrated in the near-electrode regions. It is found that the generation mechanism of intense UHF radiation in a laboratory discharge cannot be unambiguously associated with such basic processes as the head-on collision of opposite-polarity streamers or the interaction of single streamers with the near-electrode plasma at the surface of metal electrodes. We discovered that the observed UHF emission appears basically as a precursor of the intense plasma development in a certain discharge region, whereinto a bright counterstreamer comes a bit later. The findings were confirmed by the statistical observations and results of imaging the dynamics of the discharge structures with a nanosecond temporal resolution.

An apparatus for probing multipactor in X-band waveguide components

Rectangular waveguides are susceptible to avalanche-style breakdown via the multipactor phenomenon. The growth in secondary electron density produced via multipactor can damage and destroy RF components. A pulse-adjustable, hard-switched modulator powering an X-band magnetron was utilized to drive a modular experimental setup that enables testing different surface geometries and coatings. Power measurements, taken via diodes, and phase measurements, facilitated via a double-balanced mixer, were integrated into the overall apparatus enabling multipactor detection with high sensitivity and nanosecond temporal resolution. The utilized 150 kW peak microwave source with 2.5 μs pulse width and 100Hz repetition frequency allows for threshold testing without the need for initial electron seeding. This paper includes the initial results of surface conditioning of the test multipactor gap via electron bombardment.

Externally-triggerable optical pump-probe scanning tunneling microscopy with a time resolution of tens-picosecond

Photoinduced carrier dynamics of nanostructures play a crucial role in developing novel functionalities in advanced materials. Optical pump-probe scanning tunneling microscopy (OPP-STM) represents distinctive capabilities of real-space imaging of such carrier dynamics with nanoscale spatial resolution. However, combining the advanced technology of ultrafast pulsed lasers with STM for stable time-resolved measurements has remained challenging. The recent OPP-STM system, whose laser-pulse timing is electrically controlled by external triggers, has significantly simplified this combination but limited its application due to nanosecond temporal resolution. Here we report an externally-triggerable OPP-STM system with a temporal resolution in the tens-picosecond range. We also realize the stable laser illumination of the tip-sample junction by placing a position-movable aspheric lens driven by piezo actuators directly on the STM stage and by employing an optical beam stabilization system. We demonstrate the OPP-STM measurements on GaAs(110) surfaces, observing carrier dynamics with a decay time of sim 170 ps and revealing local carrier dynamics at features including a step edge and a nanoscale defect. The stable OPP-STM measurements with the tens-picosecond resolution by the electrical control of laser pulses highlight the potential capabilities of this system for investigating nanoscale carrier dynamics of a wide range of functional materials.

Self-stabilization of the equilibrium state in ferroelectric thin films

(K,Na)NbO3 is a lead-free and sustainable ferroelectric material with electromechanical parameters comparable to Pb(Zr,Ti)O3 (PZT) and other lead-based solid solutions. It is therefore a promising candidate for caloric cooling and energy harvesting applications. Specifically, the structural transition from the low-temperature Mc- to the high-temperature c-phase displays a rich hierarchical order of domains and superdomains, that forms at specific strain conditions. The relevant length scales are few tens of nanometers for the domain and few micrometers for the superdomain size, respectively. Phase-field calculations show that this hierarchical order adds to the total free energy of the solid. Thus, domains and their formation has a strong impact on the functional properties relevant for electrocaloric cooling or energy harvesting applications. However, monitoring the formation of domains and superdomains is difficult and requires both, high spatial and high temporal resolution of the experiment. Synchrotron-based time-resolved X-ray diffraction methods in combination with scanning imaging X-ray microscopy is applied to resolve the local dynamics of the domain morphology with sub-micrometer spatial and nanosecond temporal resolution. In this regime, the material displays a novel self-stabilization mechanism of the domain morphology, which may be a general property of first-order phase transitions.

Experimental and simulation study of a capacitively coupled radiofrequency plasma with a structured electrode

A low-pressure capacitively coupled radiofrequency (RF) helium discharge with a structured electrode is investigated experimentally and via kinetic simulations. In the experiment, phase resolved optical emission spectroscopy provides information about the excitation dynamics by high energy electrons, with high spatial and nanosecond temporal resolution within the RF (13.56 MHz) period. The numerical studies are based on a newly developed 2d3v particle-in-cell/Monte Carlo collisions code carried out on graphics processing units. The two approaches give consistent results for the penetration of the plasma into the trench situated in one of the electrodes and the particular electron dynamics resulting from the presence of the structured electrode. In addition, the fluxes of He+ ions and vacuum ultraviolet photons incident on the different surfaces in and around the trench structure are studied. These are discussed with respect to the homogeneous treatment of complex structures, relevant for advanced surface modification and disinfection processes.

Transient 2D Junction Temperature Distribution Measurement by Short Pulse Driving and Gated Integration with Ordinary CCD Camera.

The time resolution of the transient process is usually limited by the minimum exposure time of the high-speed camera. In this work, we proposed a method that can achieve nanosecond temporal resolution with an ordinary CCD camera by driving the LED under test with a periodic short-pulse signal and multiple-cycle superposition to obtain two-dimensional transient junction temperature distribution of the heating process. The temporal resolution is determined by the pulse width of the drive source. In the cooling process, the Boxcar gated integration principle is adopted to complete the two-dimensional transient junction temperature distribution with temporal resolution subject to the minimum exposure time of the CCD camera, i.e., 1 μs in this case. To demonstrate the validity of this method, we measured the two-dimensional transient junction temperature distribution of the blue LEDs according to the principle of thermoreflectance and compared it with the thermal imaging method.

Event-based hyperspectral EELS: towards nanosecond temporal resolution

The acquisition of a hyperspectral image is nowadays a standard technique used in the scanning transmission electron microscope. It relates the spatial position of the electron probe to the spectral data associated with it. In the case of electron energy loss spectroscopy (EELS), frame-based hyperspectral acquisition is much slower than the achievable rastering time of the scan unit (SU), which sometimes leads to undesirable effects in the sample, such as electron irradiation damage, that goes unperceived during frame acquisition. In this work, we have developed an event-based hyperspectral EELS by using a Timepix3 application-specific integrated circuit detector with two supplementary time-to-digital (TDC) lines embedded. In such a system, electron events are characterized by their positional and temporal coordinates, but TDC events only by temporal ones. By sending reference signals from the SU to the TDC line, it is possible to reconstruct the entire spectral image with SU-limited scanning pixel dwell time and thus acquire, with no additional cost, a hyperspectral image at the same rate as that of a single channel detector, such as annular dark-field. To exemplify the possibilities behind event-based hyperspectral EELS, we have studied the decomposition of calcite (CaCO$_3$) into calcium oxide (CaO) and carbon dioxide (CO$_2$) under the electron beam irradiation.

Event-based hyperspectral EELS: towards nanosecond temporal resolution

The acquisition of a hyperspectral image is nowadays a standard technique used in the scanning transmission electron microscope. It relates the spatial position of the electron probe to the spectral data associated with it. In the case of electron energy loss spectroscopy (EELS), frame-based hyperspectral acquisition is much slower than the achievable rastering time of the scan unit (SU), which sometimes leads to undesirable effects in the sample, such as electron irradiation damage, that goes unperceived during frame acquisition. In this work, we have developed an event-based hyperspectral EELS by using a Timepix3 application-specific integrated circuit detector with two supplementary time-to-digital (TDC) lines embedded. In such a system, electron events are characterized by their positional and temporal coordinates, but TDC events only by temporal ones. By sending reference signals from the SU to the TDC line, it is possible to reconstruct the entire spectral image with SU-limited scanning pixel dwell time and thus acquire, with no additional cost, a hyperspectral image at the same rate as that of a single channel detector, such as annular dark-field. To exemplify the possibilities behind event-based hyperspectral EELS, we have studied the decomposition of calcite (CaCO3) into calcium oxide (CaO) and carbon dioxide (CO2) under the electron beam irradiation.

Ultrafast Mueller matrix polarimetry with 10 nanosecond temporal resolution based on optical time-stretch.

A fastest full Mueller matrix polarimeter, to the best of our knowledge, based on optical time-stretch has been proposed and demonstrated. Thanks to the time-stretch-based ultrafast spectra detection mechanism, its measurement time could reach 10 ns. Additionally, a novel, to the best of aour knowledge, simpler method to estimate its main systematic error has been proposed and verified. With the proposed method, static measurement of polarizer and wave plate is executed with a maximum coefficient error of below 0.1. Dynamic measurement of a free space electro-optic modulator as fast-changing phase retardation has also been executed to demonstrate the feasibility of the proposed system.

Molecular Dynamics Simulations to Explore the Structure and Rheological Properties of Normal and Hyperconcentrated Airway Mucus.

We develop the first molecular dynamics model of airway mucus based on the detailed physical properties and chemical structure of the predominant gel-forming mucin MUC5B. Our airway mucus model leverages the LAMMPS open-source code [https://lammps.sandia.gov], based on the statistical physics of polymers, from single molecules to networks. On top of the LAMMPS platform, the chemical structure of MUC5B is used to superimpose proximity-based, non-covalent, transient interactions within and between the specific domains of MUC5B polymers. We explore feasible ranges of hydrophobic and electrostatic interaction strengths between MUC5B domains with 9 nanometer spatial and 1 nanosecond temporal resolution. Our goal here is to propose and test a mechanistic hypothesis for a striking clinical observation with respect to airway mucus: a 10-fold increase in non-swellable, dense structures called flakes during progression of cystic fibrosis disease. Among the myriad possible effects that might promote self-organization of MUC5B networks into flake structures, we hypothesize and confirm that the clinically confirmed increase in mucin concentration, from 1.5 to 5 mg/mL, alone is sufficient to drive the structure changes observed with scanning electron microscopy images from experimental samples. We post-process the LAMMPS simulated datasets at 1.5 and 5 mg/mL, both to image the structure transition and compare with scanning electron micrographs and to show that the 3.33-fold increase in concentration induces closer proximity of interacting electrostatic and hydrophobic domains, thereby amplifying the proximity-based strength of the interactions.

A four-channel ICCD framing camera with nanosecond temporal resolution and high spatial resolution

In this paper, a high spatial resolution, high gating speed framing camera capable of four separate two-dimensional images is designed and tested. A mirror-based image splitter has been designed and developed to provide a separate image for each arm with equal path length and equal intensity splitting while having a spectral flat response. Fast gating of a single frame is accomplished by using a proximity-focused microchannle-plate image-intensifier (MCPII) gated by a MOSFET-based pulse module with adjustable gate width from 3 ns to D.C. operation. Multiple frames are obtained by using multiple gated tubes with time intervals between consecutive frames can be adjusted flexibly. Its spatial resolution reaches 36.5 lp/mm with each frame having a 4.6-ns gate width. Furthermore, a three-dimensional MCPII model is developed to investigate the transit time and spatial resolution of the proximity-focused MCPII based on the Finite Integral Technique (FIT) and Monte Carlo method (M–C method).

Design and characterization of a resonant microwave cavity as a diagnostic for ultracold plasmas.

We present the design and commissioning of a resonant microwave cavity as a novel diagnostic for the study of ultracold plasmas. This diagnostic is based on the measurements of the shift in the resonance frequency of the cavity, induced by an ultracold plasma that is created from a laser-cooled gas inside. This method is simultaneously non-destructive, very fast (nanosecond temporal resolution), highly sensitive, and applicable to all ultracold plasmas. To create an ultracold plasma, we implement a compact magneto-optical trap based on a diffraction grating chip inside a 5GHz resonant microwave cavity. We are able to laser cool and trap (7.25 ± 0.03) × 107 rubidium atoms inside the cavity, which are turned into an ultracold plasma by two-step pulsed (nanosecond or femtosecond) photo-ionization. We present a detailed characterization of the cavity, and we demonstrate how it can be used as a fast and sensitive probe to monitor the evolution of ultracold plasmas non-destructively. The temporal resolution of the diagnostic is determined by measuring the delayed frequency shift following femtosecond photo-ionization. We find a response time of 18 ± 2 ns, which agrees well with the value determined from the cavity quality factor and resonance frequency.

RDX-Al and PETN-Al composites’ glow spectral kinetics at the explosion initiated with laser pulse

Glow spectral kinetics of cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) based composites containing aluminum nanoparticles (average diameter 100 nm) caused by explosion stimulated by neodymium laser pulse (1064 nm, 14 ns) have been studied for the first time with nanosecond temporal resolution. The experiments have been performed in the conditions of gas-dynamic relaxation hindrance. The aluminum nanoparticles, as well as the surrounding shell of the RDX and PETN, are heated during the pulse. If the laser pulse energy density is higher than the critical one, the fluorescence, whose typical relaxation time is 50 ns, appears and spectral maximum is blue-shifted with elevating the energy density of the laser pulse. The fluorescence is related to NO2● formed in the radical dissociation of RDX and PETN molecules stimulated by rapid heating in the aluminum nanoparticles explosive environment. The following exothermal decomposition reaction leads to a sample explosion in the microsecond time range. The emission spectrum of the explosion products is a thermal one with temperatures 3500 K and 3400 K for RDX-Al and PETN-Al relatively, which has been estimated using spectral pyrometry approach.

Material ejection dynamics in direct-writing of low resistivity tracks by laser-induced reverse transfer

Laser-induced reverse transfer (LIRT) is a direct-write technique for patterning materials onto transparent substrates. A laser pulse transmits through the transparent material and a small air gap to ablate a donor target surface, the vaporised target species then transfer to the transparent material. There is not yet a detailed understanding of the material ejection and deposition processes, and reports show high-resistivity films and only limited demonstration of conductive linear tracks. Here we use a recently developed capability of holographic phase contrast imaging at nanosecond temporal resolution to report the morphology of the confined ablation plume. This reveals previously unobserved phenomena such as the influence of the rebounding pressure wave and a >80% longer plasma lifetime of a confined plume, showing the importance of plume shielding and incubation effects for applications. Focusing on silver, graphite and copper, static and scanned beam experiments show the dominant role of sputtering of fragmented particles rather than vapour condensation. The results highlight the challenges in using LIRT for conformal coating without surface damage but will excite further study of this rarely explored technique, with potential for facile, reliable fabrication of conductive patterns and digitally controlled customisation of glass products for applications such as embedded sensors and electronics.

Experimental Study of Space Charge Structure and Expansion Dynamics of Laser Ablation Plasma

Using the method of spectrally selective photorecording in a nanosecond temporal resolution, the distribution of neutral atoms and single- and double-charged gallium ions in a plasma plume is investigated under the conditions of laser ablation of a gallium-indium target and so is the expansion dynamics of both components and the plume as a whole. The expansion velocity of a neutral atomic component of the plume is found. The expansion velocity of the glow boundary and the shift velocity of the glow intensity maximum are found to be close to 8.5∙103 and 6∙103 m/s, respectively. The kinetic energy range, corresponding to these values for the gallium atoms (13–26 eV) is quite consistent with the position of local maximum measured earlier from the energy distribution of single-charged gallium ions.

Synthesis and In Vitro Study of the Biodegradation Resistance of Magnetic Nanoparticles Designed for Studying the Viscoelasticity of Cytoplasm

An approach to the analysis of intracellular motion with nanosecond temporal resolution, based on the Mossbauer study of particles incorporated into a cell, has been developed. A possibility of applying magnetic nanoparticles as probes for studying in vitro the cytoplasm properties is analyzed. Two types of aqueous colloids of nanoparticles enriched with the 57Fe isotope are synthesized, and their cytotoxicity and biodegradation resistance under living cell conditions are investigated by an example of breast cancer cell line. It is found that the particles barely undergo any changes characteristic of biodegradation processes during their 120-h incubation in cells, although intracellular oxidation of divalent iron in the particle composition is observed. This result indicates possibility of using these particles for in vitro Mossbauer studies.