Optically Induced Three-Stage Picosecond Amorphization in Low-Temperature SrTiO 3
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Chemistry↗
SEARCH · Engineering Papers
Results for “picosecond”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Electric Field Effects in Hybrid Perovskites Studied via Picosecond Kerr Microscopy
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Materials Science↗
Observation of a Picosecond Light-Induced Spin Transition in Polymeric Nanorods
Spin transition (ST) materials are attractive for developing photoswitchable devices, but their slow material transformations limit device applications. Size reduction could enable faster switching, but the photoinduced dynamics at the nanoscale remains poorly understood. Here, we report a femtosecond optical pump multimodal X-ray probe study of polymeric nanorods. Simultaneously tracking the ST order parameter with X-ray emission spectroscopy and structure with X-ray diffraction, we observe photodoping of the low-spin–lattice within ~150 fs. Above a ~16% photodoping threshold, the transition to the high-spin phase occurs following an incubation period assigned to vibrational energy redistribution within the nanorods activating the molecular spin switching. Above ~60% photodoping, the incubation period disappears, and the transition completes within ~50 ps, preceded by the elastic nanorod expansion in response to the photodoping. These results support the feasibility of ST material-based GHz optical switching applications.
36 MATERIALS SCIENCE↗
Substrate Binding Stiffens Aspartate Aminotransferase by Altering the Enzyme Picosecond Vibrational Dynamics
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Picosecond volume expansion drives a later-time insulator–metal transition in a nano-textured Mott insulator
There is significant technological interest in developing ever faster switching between different electronic and magnetic states of matter. Manipulating properties at terahertz rates requires accessing the intrinsic timescales of both electrons and associated phonons, which is possible with short-pulse photoexcitation. However, in many Mott insulators, the electronic transition is accompanied by the nucleation and growth of percolating domains of the changed lattice structure, leading to empirical timescales dominated by slowly coarsening dynamics. Here, in this study, we use time-resolved X-ray diffraction and reflectivity measurements to show that the photoinduced insulator-to-metal transition in an epitaxially strained Mott insulating thin film occurs without observable domain formation and coarsening effects, allowing the study of the intrinsic electronic and lattice dynamics. Above a fluence threshold, the initial electronic excitation drives a fast lattice rearrangement, which is followed by a slower electronic evolution into a metastable nonequilibrium state. Microscopic model calculations based on time-dependent dynamical mean-field theory and semiclassical lattice dynamics explain the threshold behaviour and elucidate the delayed onset of the electronic phase transition. This work highlights the importance of combined electronic and structural studies in unravelling the physics of dynamic transitions and the timescales of photoinduced processes. During a photoinduced phase transition, electronic rearrangements are usually faster than lattice ones. Time-resolved measurements now show that the insulator-to-metal transition in a thin-film Mott insulator is preceded by lattice reconfiguration.
36 MATERIALS SCIENCE↗
Data-driven picosecond X-ray imaging for quantitative plasma-induced shock characterization
Imaging dynamic events, especially shockwave behavior, is key to advancing high-energy-density (HED) research. Recent advances in fourth- and fifth-generation X-ray light sources allow for high-resolution imaging of fast phenomena, but limited beam time necessitates maximizing data acquisition. We present a benchtop-scale pulsed plasma device submerged in liquid heptane, capable of generating dynamic events at rates exceeding 10 Hz, supporting the field’s data-driven goals by producing large, high-quality imaging datasets. Using X-ray phase contrast imaging (XPCI) at the Advanced Photon Source, we imaged weak shockwaves (Mach ~ 1.2) in heptane interacting with plasma-induced cavitation bubbles, causing deviation from Rankine-Hugoniot behavior; to our knowledge, this represents the first direct imaging of such interaction. Our quantitative analysis offers insight into weak shock phenomena and energy-focusing applications in pulsed plasmas. These results highlight the potential for large datasets to advance dynamic HED research at current light source facilities, and have implications for fields such as inertial confinement fusion, plasma-enhanced chemical processing, and biomedical applications.
36 MATERIALS SCIENCE↗
Water oxidation by a dye-catalyst diad in natural sunlight: timing and coordination of excitations and reactions across timescales of picoseconds to hours
Excitations and reactions in a dye−catalyst dyad for solar-driven water oxidation have timing mismatches caused by the stochastics of some catalytic steps. Rather than being perfectly meshed, these processes are like gears with missing teeth.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Excited-state structural conformations of Fe-amido photosensitizers revealed by picosecond X-ray absorption spectroscopy
Ultrafast X-ray spectroscopy and modelling were used to characterize distortions in the photo-generated quintet state of Fe sensitizers bearing hybrid N-heterocycle/amido ligands. Photoexcitation induces a 0.10–0.35 Å Fe–N elongation that is smaller for d(Fe–N amido ) compared to d(Fe-N heterocycle ), suggesting that the partial expansion of the Fe–N bonds involving the N-heterocyclic ligands is critical to the rapid population of ligand-field states.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Air-transfer production method for large-area picosecond photodetectors
We have designed and prototyped the process steps for the batch production of large-area micro-channel-plate photomultipliers (MCPPMT) using the “air-transfer” assembly process developed with single LAPPD TM modules. Results are presented addressing the challenges of designing a robust package that can transmit large numbers of electrical signals for pad or strip readout from inside the vacuum tube and of hermetically sealing the large-perimeter window–body interface. We have also synthesized a photocathode in a large-area low-aspect-ratio volume and have shown that the micro-channel plates recover their functionality after cathode synthesis. These steps inform a design for a multi-module batch facility employing dual nested low-vacuum and ultra-high-vacuum systems in a small-footprint. The facility design provides full access to multiple MCP-PMT modules prior to hermetic pinch-off for leak-checking and real-time photocathode optimization.
47 OTHER INSTRUMENTATION↗
Progress toward picosecond on-chip magnetic memory
Here, we offer a perspective on the prospects of ultrafast spintronics and opto-magnetism as a pathway to high-performance, energy-efficient, and non-volatile embedded memory in digital integrated circuit applications. Conventional spintronic devices, such as spin-transfer-torque magnetic-resistive random-access memory (STT-MRAM) and spin–orbit torque MRAM, are promising due to their non-volatility, energy-efficiency, and high endurance. STT-MRAMs are now entering into the commercial market; however, they are limited in write speed to the nanosecond timescale. Improvement in the write speed of spintronic devices can significantly increase their usefulness as viable alternatives to the existing CMOS-based devices. In this article, we discuss recent studies that advance the field of ultrafast spintronics and opto-magnetism. An optimized ferromagnet–ferrimagnet exchange-coupled magnetic stack, which can serve as the free layer of a magnetic tunnel junction (MTJ), can be optically switched in as fast as ~3 ps. Integration of ultrafast magnetic switching of a similar stack into an MTJ device has enabled electrical readout of the switched state using a relatively larger tunneling magnetoresistance ratio. Purely electronic ultrafast spin–orbit torque induced switching of a ferromagnet has been demonstrated using ~6 ps long charge current pulses. We conclude our Perspective by discussing some of the challenges that remain to be addressed to accelerate ultrafast spintronics technologies toward practical implementation in high-performance digital information processing systems.
42 ENGINEERING↗
Experimental verification of TNSA protons and deuterons in the multi-picosecond moderate intensity regime
Ion acceleration from high intensity short pulse laser interactions is of great interest due to a number of applications, and there has been significant work carried out with laser energies up to a few 100 J with 10's of femtosecond to 1 ps pulse durations. Here, we report results from an experiment at the OMEGA EP laser, where laser energy and pulse length were varied from 100 to 1250 J and 0.7–30 ps, respectively, in the moderate (2 × 10 17 –2 × 10 18 W/cm 2 ) laser intensity regime. Ions and electrons were simultaneously measured from disk targets made of CH and CD by a Thomson parabola and a magnetic spectrometer, respectively. Measurements showed that the electron temperature, T e (MeV), has a dependence on the laser energy, E L (J), and pulse duration, τ L (ps), and its empirical scaling was found to be 0.015 × E L 0.90 τ L –0.48. The maximum proton and deuteron energies are linearly dependent on the electron temperature, (5.60 ± 0.26) × T e and (3.17 ± 0.18) × T e , respectively. A significant increase in proton numbers with the laser energy was also observed. Furthermore, the increase in the maximum proton energy and proton count with higher energy longer duration pulses presented in this article shows that such laser conditions have a great advantage for applications, such as the proton radiograph, in the moderate laser intensity regime.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Observation of breakdown wave mechanism in avalanche ionization produced atmospheric plasma generated by a picosecond CO 2 laser
Understanding the formation and long-timescale evolution of atmospheric plasmas produced by ultrashort, long-wavelength infrared (LWIR) pulses is an important but partially understood problem. Of particular interest are plasmas produced in air with a peak laser intensity ~10 12 W/cm 2 , the so-called clamping intensity observed in LWIR atmospheric guiding experiments where tunneling and multi-photon ionization operative at near-IR or shorter wavelengths are inoperative. We find that avalanche breakdown on the surface of aerosol (dust) particles can act to seed the breakdown of air observed above the 200 GW/cm 2 threshold when a train of 3 ps 10.6 μm laser pulses separated by 18 ps is used. The breakdown first appears at the best focus but propagates backward toward the focusing optic as the plasma density approaches critical density and makes forward propagation impossible. The velocity of the backward propagating breakdown can be as high as 10 9 cm/s, an order of magnitude greater than measured with ns pulse-produced breakdown, and can be explained rather well by the so-called breakdown wave mechanism. Transverse plasma expansion with a similar velocity is assisted by UV photoionization and is observed as a secondary longitudinal breakdown mechanism in roughly 10% of the shots. When a cm-size, TW power beam is propagated, interception of aerosol particles is guaranteed and several (40 cm -3 ) breakdown sites appear, each initially producing a near-critical density plasma. On a 10 ns–1 μs timescale, shockwaves from each site expand radially and coalesce to produce a large hot gas channel. The radial velocity of the expansion agrees well with the prediction of the blast wave theory developed for ultrafast atmospheric detonations.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Picosecond magneto-optic thermometry measurements of nanoscale thermal transport in AlN thin films
The thermal conductivity Λ of wide bandgap semiconductor thin films, such as AlN, affects the performance of high-frequency devices, power devices, and optoelectronics. However, accurate measurements of Λ in thin films with sub-micrometer thicknesses and Λ > 100 W m -1 K -1 is challenging. Widely used pump/probe metrologies, such as time–domain thermoreflectance (TDTR) and frequency–domain thermoreflectance, lack the spatiotemporal resolution necessary to accurately quantify thermal properties of sub-micrometer thin films with high Λ. In this work, we use a combination of magneto-optic thermometry and TiN interfacial layers to significantly enhance the spatiotemporal resolution of pump/probe thermal transport measurements. We use our approach to measure Λ of 100, 400, and 1000 nm AlN thin films. We coat AlN thin films with a ferromagnetic thin-film transducer with the geometry of (1 nm-Pt/0.4 nm-Co) x3 /(2 nm-TiN). This PtCo/TiN transducer has a fast thermal response time of <50 ps, which allows us to differentiate between the thermal response of the transducer, AlN thin film, and substrate. For the 100, 400, and 1000 nm thick AlN films, we determine Λ to be 200 ± 80, 165 ± 35, and 300 ± 70 W m -1 K -1 , respectively. We conclude with an uncertainty analysis that quantifies the errors associated with pump/probe measurements of thermal conductivity, as a function of transducer type, thin-film thermal conductivity, and thin-film thickness. Time resolved magneto-optic Kerr effect experiments can measure films that are three to five times thinner than is possible with standard pump/probe metrologies, such as TDTR. This advance in metrology will enable better characterization of nanoscale heat transfer in high thermal conductivity material systems like wide bandgap semiconductor heterostructures and devices.
36 MATERIALS SCIENCE↗
Laser material interactions in tamped materials on picosecond time scales in aluminum
Here, a 100 ps laser is used to probe the pressure generation, depth of the non-solid ablator, and the non-linear optical effects through tamper materials. Samples consisted of an aluminum ablator with tampers of sapphire and coverslip glass. In general, the sapphire tamped sample achieves higher pressures at lower laser intensities as compared to the coverslip glass tamped sample. Attempts to model the details of this set of experimental data with standard available radiation coupled hydrodynamic codes make clear that more physics is needed in these simulations to accurately predict the impact of the tamper material on the pressure generation and the depth of non-solid aluminum.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Performance of a Front End prototype ASIC for picosecond precision time measurements with LGAD sensors
For the High-Luminosity phase of LHC, the ATLAS experiment is proposing the addition of a High Granularity Timing Detector (HGTD) in the forward region, to mitigate the effects of the increased pile-up. The chosen detection technology is Low Gain Avalanche Detector (LGAD) silicon sensors that can provide an excellent timing resolution below 50 ps. The front-end read-out ASIC must exploit the large signal derivative and small noise provided by the sensor, while keeping low power consumption. This paper presents the results on the first prototype of a front-end ASIC, named ALTIROC0, which contains the analog stages (preamplifier and discriminator) of the read-out chip. The ASIC was characterised both alone and as part of a module with a 2×2 LGAD array of 1.1×1.1 mm 2 pads bump-bonded to it. The various contributions of the electronics to the time resolution were investigated in test-bench measurements with a calibration setup. Both when the ASIC is alone or with a bump-bonded sensor, the jitter of the ASIC is better than 20 ps for an injected charge of 10 fC. The time walk effect, which arises from the different preamplifier response for various injected charges, can be corrected up to 10 ps using a Time Over Threshold measurement. The combined performance of the ASIC and the LGAD sensor, which was measured during a beam test campaign in October 2018 with pions of 120 GeV energy at the CERN SPS, is around 40 ps for all measured modules. All tested modules show good efficiency and time resolution uniformity.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Picosecond Timing Resolution Measurements of Low Gain Avalanche Detectors with a 120 GeV Proton Beam for the TOPSiDE Detector Concept
This paper presents results that take a critical step toward proving 10 ps timing resolution’s feasibility for particle identification in the TOPSiDE detector concept for the Electron-Ion Collider. Measurements of LGADs with a thickness of 35 μm and 50 μm are evaluated with a 120 GeV proton beam. The performance of the gain and timing response is assessed, including the dependence on the reverse bias voltage and operating temperature. The best timing resolution of UFSDs in a test beam to date is achieved using three combined planes of 35 μm thick LGADs at -30°C with a precision of 14.3 ± 1.5 ps.
Particle tracking detectors↗