Nanosecond Time Resolution Research Articles

Electric field and rotational temperature measurements based on electric field-induced coherent anti-Stokes Raman scattering in visible region (E-CARSv) in hydrogen discharge plasmas

Electric field measurements with a time resolution of a few nanoseconds using an electric field-induced coherent anti-Stokes Raman scattering in the visible region (E-CARSv) scheme were performed in a repetitively pulsed nanosecond discharge plasma in a 0.3-atm hydrogen environment. The rotational temperature was estimated using the E-CARSv scheme, which enables us to extract electric fields even at elevated gas temperatures. The estimated rotational temperature was 390 K, which reduced the E-CARSv signal intensity by approximately 50% when the rotational temperature was equal to the gas temperature. Considering the reduction, the peak electric field was estimated to be −1.4 kV/mm, which is 40% higher than −1.0 kV/mm, assuming no elevated temperatures.

Probing the Operation of Quantum-Dot Light-Emitting Diodes Using Electrically Pumped Transient Absorption Spectroscopy.

The quantum-dot light-emitting diode (QLED) is a new generation light emission source that holds great promise for display and lighting applications. Understanding the dynamics of electrons and holes in QLEDs during their operation is crucial for future QLED optimization, but a time-resolved technology capable of characterizing electrons is still lacking. To tackle this challenge, we develop a unique electrically pumped transient absorption (E-TA) spectroscopy to probe the density of electrons in the QD layer with a nanosecond time resolution. The E-TA result provides a comprehensive understanding of the electron dynamics in QLEDs by quantifying the electron injection time after external voltage on, electron release time after external voltage off, and equilibrated electron density (Ne) in the QD layer during device operation. By combining E-TA technology with time-resolved electroluminescence and transient current measurements, we present a comprehensive overview of the dynamics of both electrons and holes in a QLED during operation.

Fast Multi-Wavelength Pyrometer for Dynamic Temperature Measurements

Multi-wavelength pyrometry is an efficient tool for measuring high temperatures in dynamic experiments. A fast 5-channel pyrometer was built and successfully employed in ion-beam heating experiments at the GSI Centre for Heavy Ion Research (Darmstadt, Germany). Temperatures of metallic samples heated by an intense focused heavy ion beam up to their melting points and beyond were measured with nanosecond time resolution and a spatial resolution of about 200 μm. The modular instrument has demonstrated its high versatility also for temperature measurements of exothermic reactions with millisecond temporal resolution.

Single particle inductively coupled plasma mass spectrometry with nanosecond time resolution

We present a new data acquisition unit with nanosecond time resolution (nanoDAQ) for single particle inductively coupled plasma mass spectrometry (spICP-MS), which is able to detect gold nanoparticles below 10 nm with a single quadrupole ICP-MS.

Beam diagnostics with silicon pixel detector array at PADME experiment

During 2022 data taking (Run III) PADME searched for a resonant production and a visible decay of the X17 particle into e+e-. A precise knowledge within 1% uncertainty of the number of positrons was required for the observation. To that purpose, an array of 2 × 6 Timepix3 (total of 512 × 1536 pixels) hybrid pixel detectors operated in data-streaming mode with ToA resolution of 1.56 ns for every pixel was employed. Two methods for data acquisition were developed. A frame-based method, integrating the number of hits for each individual pixel for a predefined period of time served for monitoring the beam conditions and to provide a rough estimation of the beam distribution and number of positrons. A data streaming mode exploiting the nanosecond time resolution of Timepix3 detector was used for precise characterization of the transverse beam profile and the distribution of the incident positrons within each bunch of ∼ 200 ns duration.

Time-Resolved Structural Measurement of Thermal Resistance across a Buried Semiconductor Heterostructure Interface

The precise control and understanding of heat flow in heterostructures is pivotal for advancements in thermoelectric energy conversion, thermal barrier coatings, and efficient heat management in electronic and optoelectronic devices. In this study, we employ high-angular-resolution time-resolved X-ray diffraction to structurally measure thermal resistance in a laser-excited AlGaAs/GaAs semiconductor heterostructure. Our methodology offers femtometer-scale spatial sensitivity and nanosecond time resolution, enabling us to directly observe heat transport across a buried interface. We corroborate established Thermal Boundary Resistance (TBR) values for AlGaAs/GaAs heterostructures and demonstrate that TBR arises from material property discrepancies on either side of a nearly flawless atomic interface. This work not only sheds light on the fundamental mechanisms governing heat flow across buried interfaces but also presents a robust experimental framework that can be extended to other heterostructure systems, paving the way for optimized thermal management in next-generation devices.

2D Perovskite Neutron Scintillators with Nanosecond Time Resolution and Linearity Energy Response

AbstractFast and high‐linearity detection of fast neutron is vital for special nuclear material seeking, nuclear accident emergency response, nondestructive neutron imaging, and neutron cancer therapy. Neutron scintillators with fast time resolution and linear energy response are indispensable for precisely acquiring the energy and temporal evolution of fast neutron, but none of the conventional neutron scintillators, whether organic, two‐component or inorganic, have performed well in this regard. To address these challenges, it is urgent to develop novel neutron scintillators. Here, 2D hybrid perovskite single crystals (C4H12N)2PbBr4 (BA2PbBr4) successfully combined with fast response time of 2.66 ns and linear energy response to fast neutrons, γ ray, and α particle, is reported. The rapid response time and linear energy response of 2D hybrid perovskite scintillator originate from intensive states density of lead halide frameworks, which are the key fluorescence emitters under neutron irradiation. This effectively suppresses the ionization quenching effect during the fluorescence process. This work represents a milestone in fast neutron detection, demonstrating a new type of neutron scintillator based on 2D hybrid perovskite single crystals with fast and high‐linearity detection characteristics, having great potential in high precision neutron spectrum measurement and nuclear reaction kinetics monitoring.

Real-time electron clustering in an event-driven hybrid pixel detector

Event-driven hybrid pixel detectors with nanosecond time resolution have opened up novel pathways in modern ultrafast electron microscopy, for example in hyperspectral electron-energy loss spectroscopy or free-electron quantum optics. However, the impinging electrons typically excite more than one pixel of the device, and an efficient algorithm is therefore needed to convert the measured pixel hits to real single-electron events. Here we present a robust clustering algorithm that is fast enough to find clusters in a continuous stream of raw data in real time. Each tuple of position and arrival time from the detector is continuously compared to a buffer of previous hits until the probability of a merger with an old event becomes irrelevant. In this way, the computation time becomes independent of the density of electron arrival and the algorithm does not break the operation chain. We showcase the performance of the algorithm with a ‘timepix’ camera in two regimes of electron microscopy, in continuous beam emission and laser-triggered femtosecond mode.

Mid-IR quantum cascade laser spectroscopy to resolve lipid dynamics during the photocycle of bacteriorhodopsin.

Membranes are crucial for the functionality of membrane proteins in several cellular processes. Time-resolved infrared (IR) spectroscopy enables the investigation of interaction-induced dynamics of the protein and the lipid membrane. The photoreceptor and proton pump bacteriorhodopsin (BR) was reconstituted into liposomes, mimicking the native purple membrane. By utilization of deuterated lipid alkyl chains, corresponding vibrational modes are frequency-shifted into a spectrally silent window that allows us to monitor lipid dynamics during the photoreaction of BR. Our home-built quantum cascade laser (QCL)-based IR spectrometer covers all relevant spectral regions to detect both lipid and protein vibrational modes. QCL-probed transients at single wavenumbers are compared with the previously performed step-scan Fourier-transform IR measurements. The absorbance changes of the lipids could be resolved by QCL-measurements with a much better signal-to-noise ratio and with nanosecond time resolution. We found a correlation of the lipid dynamics with the protonation dynamics in the M intermediate. QCL spectroscopy extends the study of the protein's photocycle toward dynamics of the interacting membrane.

Effects of plasma expansion plumes in view of pulses laser irradiating centimeter-scale spherical space debris

The objective of this article was to investigate the dynamic evolution behaviors of plasma expansion plumes by pulses laser irradiating centimeter-scale spherical space debris. A calculated model of centimeter-scale spherical space debris irradiated by pulses laser was firstly deduced based on FEM (finite element method)/COMSOL, and the action rules of plasma expansion plumes by pulses laser-generated irradiating the debris were simulated for different laser powers and action times. The results showed that the velocity of plasma expansion plumes was increased with the increase of laser powers and action times. Especially, when the laser power was 700 kW and the action time was close to 25 μs, the maximum velocity of plasma expansion plumes approached 1.91 km/s, and the diffusion radius of plasma expansion plumes was increased by about 2.5 mm. Further, the diffusion radius was about twice that of 400 kW when the action time reached about 48 μs. As a result, by simulating the transient flow process of nanosecond pulses laser irradiating small spherical space debris, the flow field evolution information and plasma plumes evolution characteristics of centimeter-scale space debris at nanosecond time resolution were revealed.

Intensified Tpx3Cam, a fast data-driven optical camera with nanosecond timing resolution for single photon detection in quantum applications

We describe a fast data-driven optical camera, Tpx3Cam, with nanosecond scale timing resolution and 80 Mpixel/sec throughput. After the addition of intensifier, the camera is single photon sensitive with quantum efficiency determined primarily by the intensifier photocathode. The single photon performance of the camera was characterized with results on the gain, timing resolution and afterpulsing reported here. The intensified camera was successfully used for measurements in a variety of applications including quantum applications. As an example of such application, which requires simultaneous detection of multiple photons, we describe registration of photon pairs from the spontaneous parametric down-conversion source in a spectrometer. We measured the photon wavelength and timing with respective precisions of 0.15 nm and 3 ns, and also demonstrated that the two photons are anti-correlated in energy.

Investigation of the afterpeaks in pulsed microwave argon plasma at atmospheric pressure

We studied the energy transport process in pulsed microwave argon plasmas at atmospheric pressure, focusing on the optical emission burst during the pulse-off time called the afterpeak. Guided by experimental observations using nanosecond time resolution imaging and spectroscopic diagnostics, we developed a global simulation model considering time-varying reaction rate coefficients and non-thermal electron energy distribution. Experimental and simulation results show that the afterpeak can be maximized by choosing an appropriate pulse period. Our analysis of the generation and consumption of excited argon species reveals that the rapid drop in electron temperature during the inter-pulse time reduces the diffusive loss of ions and enhances the recombination reactions, which produce the afterpeak. We also reveal that the radiation trapping and high energy level argon must be considered to simulate the afterpeak in atmospheric conditions. The improved understanding of the afterpeak dynamics can be utilized to optimize the power coupling and/or generation of reactive species.

Amplitude–Temporal and Spectral Characteristics of Pulsed UHF-SHF Radiation of a High-Voltage Streamer Discharge in Air under the Atmospheric Pressure

A special experimental setup with a three-electrode discharge gap was used to study the dynamic characteristics of the ultra-high- and super-high-frequency (UHF-SHF) electromagnetic radiation of a high-voltage discharge having the streamer form with reference to the dynamics of individual streamers at the nanosecond time resolution. We performed synchronous detection of the radiation waveforms using a wideband horn antenna, on the one hand, and high-speed photography of the discharge development in the discharge gap using an ICCD camera, on the other hand. It was found that the high-voltage discharge is a source of radiation in the frequency band up to 10 GHz, which is a series of individual ultrawideband (UWB) bursts having durations of less than 1 ns and leading fronts less than 100 ps long and appears when the streamers moving from the discharge anode (thin wire) meet the discharge cathode (plane). By the order of magnitude, the number of radiation bursts corresponds to the number of streamers that reach the electrode, according to the high-speed photography data. The qualitative data confirmed by simple theoretical estimations show that the sources of UWB radiation pulses are individual streamers at the moment of their contact with the electrode, and the radiation of the streamers can be regarded as transition radiation.

A Method for Investigating Nanosecond Processes in Micropinch Discharge Plasma

The technique is described and the results of studies of the spatial structure and dynamics of X-ray sources in the plasma of a micropinch discharge are presented. The applied technique made it possible to temporarily link the process of electron acceleration in a quasi-static electric field of a resistive nature to the process of forming a microstretch in a Z-pinch in a medium of heavy elements with a nanosecond time resolution.

Mechanisms driving self-organization phenomena in random plasmonic metasurfaces under multipulse femtosecond laser exposure: a multitime scale study

Abstract Laser-induced transformations of plasmonic metasurfaces pave the way for controlling their anisotropic optical response with a micrometric resolution over large surfaces. Understanding the transient state of matter is crucial to optimize laser processing and reach specific optical properties. This article proposes an experimental and numerical study to follow and explain the diverse irreversible transformations encountered by a random plasmonic metasurface submitted to multiple femtosecond laser pulses at a high repetition rate. A pump-probe spectroscopic imaging setup records pulse after pulse, and with a nanosecond time resolution, the polarized transmission spectra of the plasmonic metasurface, submitted to 50,000 ultrashort laser pulses at 75 kHz. The measurements reveal different regimes, occurring in different ranges of accumulated pulse numbers, where successive self-organized embedded periodic nanostructures with very different periods are observed by post-mortem electron microscopy characterizations. Analyses are carried out; thanks to laser-induced temperature rise simulations and calculations of the mode effective indices that can be guided in the structure. The overall study provides a detailed insight into successive mechanisms leading to shape transformation and self-organization in the system, their respective predominance as a function of the laser-induced temperature relative to the melting temperature of metallic nanoparticles and their kinetics. The article also demonstrates the dependence of the self-organized period on the guided-mode effective index, which approaches a resonance due to system transformation. Such anisotropic plasmonic metasurfaces have a great potential for security printing or data storage, and better understanding their formation opens the way to smart optimization of their properties.

Laser-induced photodetachment of negative oxygen ions in the spatial afterglow of an atmospheric pressure plasma jet

Negative ions are an important constituent of the spatial afterglow of atmospheric pressure plasmas, where the fundamental plasma-substrate interactions take place that are vital for applications such as biomedicine, material synthesis, and ambient air treatment. In this work, we use laser-induced photodetachment to liberate electrons from negative ions in the afterglow region of an atmospheric pressure plasma jet interacting with an argon-oxygen mixture, and microwave cavity resonance spectroscopy to detect the photodetached electrons. This diagnostic technique allows for the determination of the electron density and the effective collision frequency before, during and after the laser pulse was shot through the measurement volume with nanosecond time resolution. From a laser saturation study, it is concluded that O− is the dominant negative ion in the afterglow. Moreover, the decay of the photodetached electron density is found to be dominantly driven by the (re)formation of O− by dissociative attachment of electrons with O2. As a consequence, we identified the species and process responsible for the formation of negative ions in the spatial afterglow in our experiment.

Fast shadow visualization of a pulsed discharge in a short gas gap

A study of the switching process of a short (1 mm) gas gap initiated by a spark discharge along the dielectric surface was carried out by the method of shadowgraphy with nanosecond time resolution. The presence of a shock wave propagating from the cathode spot and signs of intermediate accumulation of the invested energy in the form of excitation energy of gas molecules or turbulent gas flow were detected. Keywords: shadowgraphy, gas discharge, shock waves, switch.

Быстрая теневая визуализация импульсного разряда в коротком газовом промежутке

A study of the switching process of a short (1 mm) gas gap initiated by a spark discharge along the dielectric surface was carried out by the method of shadowgraphy with nanosecond time resolution. The presence of a shock wave propagating from the cathode spot and signs of intermediate accumulation of the invested energy in the form of excitation energy of gas molecules or turbulent gas flow were detected.

Observation of photoemission behaviour during avalanche breakdown of insulated gate bipolar transistor with defect in the metal contact

Under unclamped inductive switching (UIS) condition, there is non-uniformity in the intra-chip distribution of avalanche breakdown current in insulated gate bipolar transistors (IGBTs). The “current filaments”, which are concentrations of current caused by the parasitic PNP transistor, move through the chip and are thought to be related to failures. During the avalanche breakdown, the charge bremsstrahlung generates light over a wide wavelength range. We have previously reported that we constructed an observation system using a photomultiplier tube (PMT) and observed the avalanche breakdown photoemission with nanosecond time resolution. In this study, we used the same observation system to observe the photoemission behaviour of the samples in which the metal electrode was partially removed with a FIB (focused ion beam) to create a defective contact area. In the sample with the pseudo-defect, (a) there was an abnormal emission peak that did not correspond to the avalanche current change, (b) the randomness of the behaviour for each single pulse became extremely low, and (c) the pseudo-defect itself did not trap the current filament. These results may explain the tendency of IGBTs to have a higher probability of failure during repetitive avalanche breakdowns if they contain some defects.

High speed imaging of spectral-temporal correlations in Hong-Ou-Mandel interference.

In this work we demonstrate spectral-temporal correlation measurements of the Hong-Ou-Mandel (HOM) interference effect with the use of a spectrometer based on a photon-counting camera. This setup allows us to take, within seconds, spectral temporal correlation measurements on entangled photon sources with sub-nanometer spectral resolution and nanosecond timing resolution. Through post processing, we can observe the HOM behaviour for any number of spectral filters of any shape and width at any wavelength over the observable spectral range. Our setup also offers great versatility in that it is capable of operating at a wide spectral range from the visible to the near infrared and does not require a pulsed pump laser for timing purposes. This work offers the ability to gain large amounts of spectral and temporal information from a HOM interferometer quickly and efficiently and will be a very useful tool for many quantum technology applications and fundamental quantum optics research.