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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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368 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Investigating the ultraviolet photodissociation of bromocyclopropane with ultrafast electron diffraction

We have studied the photodissociation of gas-phase bromocyclopropane by 200 nm wavelength ultraviolet radiation using ultrafast electron diffraction. Bromocyclopropane is a prototypical molecule in the study of organobromides, a class of molecules that have a significant impact on atmospheric ozone depletion through their photochemistry. Here, previous studies have revealed two possible reaction pathways for the photodissociation of bromine from bromocyclopropane; either the C–Br bond dissociates, leaving behind a cyclopropyl ring, or there is a concerted opening of the cyclopropyl ring along with the C–Br bond dissociation. In this work, both our experimental and simulation results indicate that the majority of the UV-photoexcited BCP molecules (88% ± 11% in the experiment) follow the first reaction pathway, in which the cyclopropyl ring remains closed after homolytic C–Br bond cleavage. This direct bond dissociation occurs within the experimental time resolution of 270 fs. In order to differentiate between the possible reaction end-products, both of which have diffraction signals dominated by the bromine atom, a new analysis method has been employed, which is more sensitive to the structure of the end-products.

Atmospheric chemistry↗
DOE OSTI2026

Deep-ultraviolet ptychographic pocket-scope (DART): mesoscale lensless molecular imaging with label-free spectroscopic contrast

The mesoscale characterization of biological specimens has traditionally required compromises between resolution, field-of-view, depth-of-field, and molecular specificity, with most approaches relying on external labels. Here we present the Deep-ultrAviolet ptychogRaphic pockeT-scope (DART), a handheld platform that transforms label-free molecular imaging through intrinsic deep-ultraviolet spectroscopic contrast. By leveraging biomolecules’ natural absorption fingerprints and combining them with lensless ptychographic microscopy, DART resolves down to 308-nm linewidths across centimeter-scale areas while maintaining millimeter-scale depth-of-field. The system’s virtual error-bin methodology effectively eliminates artifacts from limited temporal coherence and other optical imperfections, enabling high-fidelity molecular imaging without lenses. Through differential spectroscopic imaging at deep-ultraviolet wavelengths, DART quantitatively maps nucleic acid and protein distributions with femtogram sensitivity, providing an intrinsic basis for explainable virtual staining. We demonstrate DART’s capabilities through imaging of tissue sections, cytopathology specimens, blood cells, and neural populations, revealing detailed molecular contrast without external labels. The combination of high-resolution molecular mapping and broad mesoscale imaging in a portable platform opens new possibilities from rapid clinical diagnostics, tissue analysis, to biological characterization in space exploration.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Quantum beats in two-color photoionization to the spin-orbit split continuum of Ar

We report a study of the quantum beats in two-color photoionization of argon. An attosecond extreme ultraviolet pulse train prepares an electronic wave packet of definite odd parity, with total angular momentum J = 1, targeting the states between 14.0 and 14.5 eV from the ground state. Two-photon ionization of this wave packet with a tunable infrared probe pulse makes the constituent states interfere in both continuum channels, corresponding to the core angular momenta j c = 1/2 and 3/2, respectively. We analyze photoelectron spectrograms as a function of the time delay of the probe pulse and identify oscillations due to several pairs of states through Fourier decomposition. We observe phase differences between the corresponding beat signals in the two spin-orbit split continua. Comparison of theoretical simulations with the experimental measurements allows us to interpret the amplitudes and phases of ionization signals. Furthermore, we express the observed phase differences in terms of the off-diagonal elements of the short-range scattering matrix and the dipole matrix elements to the continuum eigenchannels.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

EUV debris mitigation using magnetic nulls

Next generation EUV sources for photolithography use light produced by laser-produced plasmas (LPP) from ablated tin droplets. A major challenge for extending the lifetime of these devices is mitigating damage caused by deposition of tin debris on the sensitive collection mirror. Especially difficult to stop are high energy (up to 10 keV) highly charged tin ions created in the plasma. Existing solutions include the use of stopping gas, electric fields, and magnetic fields. One common configuration consists of a magnetic field perpendicular to the EUV emission direction, but such a system can result in ion populations that are trapped rather than removed. Here we investigate a previously unconsidered mitigation geometry consisting of a magnetic null by performing full-orbit integration of the ion trajectories in an EUV system with realistic dimensions and optimize the coil locations for the null configuration. The magnetic null prevents a fraction of ions from hitting the mirror comparable to that of the perpendicular field, but does not trap any ions due to the chaotic nature of ion trajectories that pass close to the null. This technology can potentially improve LPP-based EUV photolithography system efficiency and lifetime and may allow for a different, more efficient formulation of buffer gas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Time-resolved momentum imaging of UV photodynamics in structural isomers of iodopropane probed by site-selective XUV ionization

The photodynamics of 1- and 2-iodopropane (1 and 2-IP) were studied in a time-resolved scheme incorporating ultraviolet (UV) excitation and extreme ultraviolet (XUV) probing, which initiates photoionization selectively from the I 4d core orbital. UV absorption in the A-band of both isomers leads to prompt C–I bond fission, with significant disposal of internal energy into the propyl radical product. Site-selective ionization enables a range of charge transfer (CT) processes between the nascent highly charged iodine ions and neutral propyl radicals, dependent on the interfragment distance at the instant of ionization. Subtle differences in the dynamics of these CT processes between the two isomers are observed. In 1-IP, the kinetic energies of iodine ions produced by UV photodissociation and subsequent XUV multiple ionization increased notably over the first few hundred femtoseconds, which could be understood in terms of differing gradients along the photodissociation coordinates of the neutral and polycationic states involved in the pump and probe steps, respectively. Led by a recent report of HI elimination in UV photoexcited 2-IP [Todt et al., Phys. Chem. Chem. Phys., 22(46), 27338 (2020)], we also model the most likely signatures of this process in the present experiment, and can identify signal in the 2-IP data (that is absent or significantly weaker in the data from the unbranched 1-IP isomer) that is consistent with such a process occurring on ultrafast timescales.

Allum, Felix [Deutsches Elektronen-Synchrotron (DE↗
DOE OSTI2022

State-selective probing of CO 2 autoionizing inner valence Rydberg states with attosecond extreme ultraviolet four-wave-mixing spectroscopy

Nonlinear spectroscopies can disentangle spectra that are congested due to inhomogeneous broadening. Here, in conjunction with theoretical calculations, attosecond extreme ultraviolet (XUV) four-wave-mixing (FWM) spectroscopy is utilized to probe the dynamics of autoionizing inner valence excited Rydberg states of the polyatomic molecule, CO 2 . This tabletop nonlinear technique employs a short attosecond XUV pulse train and two noncollinear, few-cycle near-infrared pulses to generate background-free XUV wave-mixing signals. FWM emission is observed from the n=5-7 states of the Henning sharp ndσ g Rydberg series that converges to the ionic $\widetilde{B}$ 2 Σ$^{+}_{u}$ state. However, these transient emission signals decay with lifetimes of 33 ± 6, 53 ± 2, and 94 ± 2 fs, respectively, which calculations show are consistent with the lifetimes of the short-lived n=6-8 members of the nsσ g character Henning diffuse Rydberg series. The oscillator strengths of transitions between states involved in all possible resonant FWM processes are calculated, verifying that the nonlinear spectra are dominated by pathways described by an initial excitation to the diffuse nsσ g Rydberg series and emission from the sharp ndσ g Rydberg series. The results substantiate not only that attosecond XUV FWM spectroscopy produces rigorous and meaningful measurements of ultrafast dynamics in polyatomic systems, but also that nonlinear spectroscopic techniques are versatile tools to selectively probe dynamics that are otherwise difficult to access.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Characterization of PuO 2 With Visible and UV Raman Spectroscopy: Discrimination Between the Bulk, Surface, and an Intermediate Disordered Layer

Raman spectroscopy is an ideal tool in the characterization of materials including PuO 2 . The wavelength-dependent absorptivity of the material defines the light penetration depth and the relative Raman scattering contribution from the bulk and the surface. Here, the surface contribution to the total Raman scattering was investigated for PuO 2 calcined at various temperatures and recorded with laser wavelengths of 355, 325, and 244 nm. These experiments provided the first glimpse of the wavelength-dependent disappearance and emergence of new phonons and electronic bands from the PuO 2 surface layers. The first indication of the wavelength transition in the Raman spectra was the loss of the 2LO2 (overtone, ~1155 cm -1 ) band and the weakening intensity of the Г 1 → Γ 5 electronic band (~2135 cm -1 ) with the 355-nm excitation laser. The Γ 5 electronic band was barely visible with the 244-nm excitation. The electronic band located at ~1050 cm -1 , corresponding to the Г 1 → Γ 4 electronic transition was observed to dramatically increase in intensity while the Г 1 → Γ 3 electronic band (2640 cm -1 ) sharpened as the UV wavelength was increased in energy from the near- to deep-UV (355–325–244 nm). The FWHM of the T 2g band was found to vary with calcination temperature (450°C and 900°C) with the 325-nm laser and the 244-nm laser. The T 2g band attributes, the strong emergence of the Г 1 → Γ 4 electronic band, and the disappearance of the 2LO2 overtone acquired with the 244-nm excitation for the different calcination temperatures suggest a shallow penetration depth.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

SN 2018fif: The Explosion of a Large Red Supergiant Discovered in Its Infancy by the Zwicky Transient Facility

High-cadence transient surveys are able to capture supernovae closer to their first light than ever before. Applying analytical models to such early emission, we can constrain the progenitor stars' properties. Here, we present observations of SN 2018fif (ZTF 18abokyfk). The supernova was discovered close to first light and monitored by the Zwicky Transient Facility (ZTF) and the Neil Gehrels Swift Observatory. Early spectroscopic observations suggest that the progenitor of SN 2018fif was surrounded by relatively small amounts of circumstellar material compared to all previous cases. This particularity, coupled with the high-cadence multiple-band coverage, makes it a good candidate to investigate using shock-cooling models. We employ the SOPRANOS code, an implementation of the model by Sapir & Waxman and its extension to early times by Morag et al. Compared with previous implementations, SOPRANOS has the advantage of including a careful account of the limited temporal validity domain of the shock-cooling model as well as allowing usage of the entirety of the early UV data. We find that the progenitor of SN 2018fif was a large red supergiant with a radius of $R={744.0}_{-128.0}^{+183.0}\,{R}_{\odot }$ and an ejected mass of ${M}_{\mathrm{ej}}={9.3}_{-5.8}^{+0.4}\,{M}_{\odot }$. Our model also gives information on the explosion epoch, the progenitor's inner structure, the shock velocity, and the extinction. The distribution of radii is double-peaked, with smaller radii corresponding to lower values of the extinction, earlier recombination times, and a better match to the early UV data. If these correlations persist in future objects, denser spectroscopic monitoring constraining the time of recombination, as well as accurate UV observations (e.g., with ULTRASAT), will help break the extinction/radius degeneracy and independently determine both.

79 ASTRONOMY AND ASTROPHYSICS↗