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DOE OSTI2022

Energy scaling beyond the gas ionization threshold with divided-pulse nonlinear compression

Here, we demonstrate how pulse energy in hollow-core fiber can be scaled beyond gas-ionization limitations using divided-pulse nonlinear compression. With one pulse, ionization limits our fiber’s pulse energy to 2.7-mJ output at an input of 4 mJ. By dividing to four low-energy pulses before the fiber, we eliminated the ionization and scaled the pulse energy 2.5× to 6.6 mJ at an input energy of 10 mJ. Larger energy scaling is possible, as our maximum pulse energy has not reached the new gas ionization threshold. Our results motivate applying the method to state-of-the-art systems for large pulse energy scaling without prohibitive system size increases.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Intense quasi-monochromatic resonant harmonic generation in the multiphoton ionization regime

Resonant high-order harmonics, which result in quasimonochromatic extreme ultraviolet light with coherent intensity enhancement involving autoionizing resonances, have been demonstrated from laser-ablated plumes in the tunnel-ionization regime. Here, we demonstrate resonant harmonics in the previously unexplored multiphoton-ionization regime. We demonstrate an intense resonant harmonic from gallium with an intensity enhancement ratio of 714 relative to the neighboring harmonics, achieved without the need for extreme ultraviolet filtering methods, thus preventing a typical photon flux loss of more than 70%. Three-dimensional time-dependent Schrödinger equation calculations reveal that this increase in the enhancement ratio is due to the lowelectron wave packet spreading in the multiphoton-ionization regime. These results reveal a method for increasing the intensity and monochromaticity of intense multimicrojoule femtosecond extreme ultraviolet light and will also facilitate understanding of the involvement of autoionizing resonances in generating resonant harmonics in the multiphoton-ionization regime.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2026

New correlated numerical methods for attosecond molecular single and double ionization

This project resulted in the development of ASTRA, a new molecular ionization code capable of describing single and double ionization processes in polyatomic molecules with correlated electrons and time-dependent fields. Key achievements include: (i) the development of the PRISM hybrid-integral library enabling core-ionization and high-angular-momentum convergence; (ii) implementation of time-dependent Schrödinger equation solvers for pump–probe spectroscopies; (iii) validation against experimental and theoretical benchmarks for atoms and molecules; and (iv) extension to two-photon double ionization using the finite-pulse virtual-sequential model. These developments establish ASTRA as a versatile platform for attosecond molecular dynamics.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2024

Measurement of Ionization Produced by 254 eVnr Nuclear Recoils in Germanium

Ionization produced by low-energy nuclear recoils is among the primary direct signatures of dark matter interactions. Despite the urgency of dark matter detection and the recent measurements of coherent elastic neutrino-nucleus scattering, detector response to nuclear recoils is not well characterized in the keVnr and sub-keVnr regime across a variety of materials. We have re-performed a measurement of the ionization produced by monoenergetic 254 eVnr nuclear recoils in Ge with improved digital electronics and additional systematic studies. Our results indicate an ionization yield of 64 +/- 8 eVee corresponding to a quenching factor of 25 +/- 3%, greater than the 14% predicted by the Lindhard model. This ionization enhancement could greatly improve the sensitivity of high-purity Ge detectors in dark matter detection and measurement of neutrinos via coherent scattering.

Kavner, Alexander R.↗

DOE OSTI2020

Device and system for selective ionization and analyte detection and method of using the same

Disclosed herein are embodiments of a system for selectively ionizing samples that may comprise a plurality of different analytes that are not normally detectable using the same ionization technique. The disclosed system comprises a unique split flow tube that can be coupled with a plurality of ionization sources to facilitate using different ionization techniques for the same sample. Also disclosed herein are embodiments of a method for determining the presence of analytes in a sample, wherein the number and type of detectable analytes that can be identified is increased and sensitivity and selectivity are not sacrificed.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗

DOE OSTI2021

Ionizing-radiation beam monitoring system

Embodiments are directed generally to an ionizing-radiation beam monitoring system that includes an enclosure structure with at least one ultra-thin window to an incident ionizing-radiation beam. Embodiments further include at least one scintillator within the enclosure structure that is substantially directly in an incident ionizing-radiation beam path and at least one ultraviolet illumination source within the enclosure structure and facing the scintillator. At least one pixelated imaging system within the enclosure structure is located out of an incident ionizing-radiation beam path and includes at least one pixelated photosensor device optically coupled to an imaging lens.

Friedman, Peter S.↗

DOE OSTI2021

Device and system for selective ionization and analyte detection and method of using the same

Denis, Elizabeth↗

DOE OSTI2021

Search for Lightly Ionizing Particles in SuperCDMS and simulation of neutron backgrounds

The Super Cryogenic Dark Matter Search (SuperCDMS) is a direct-detection dark matter search experiment that primarily aims to search for Weakly Interacting Massive Particles (WIMPs) using state-of-the-art solid-state detection technology. During its operation at the Soudan underground laboratory, germanium detectors were operated with high bias voltage mode known as the CDMS low ionization threshold experiment (CDMSlite) to achieve below-keV thresholds. CDMSlite, for being able to measure small energy depositions in detectors, also provides sensitivity to Lightly Ionizing Particles (LIPs) with very small fractional charges. This thesis will discuss an analysis to search LIPs with the data acquired in CDMSlite mode. An important component for LIPs search is the expected energy-deposition distributions for LIPs falling on the CDMSlite detector. In this thesis, a simulation framework to calculate the energy-deposition distributions is developed. This thesis presents first direct-detection limits on the intensity of cosmogenic LIPs with electric charges smaller than e /(3 × 10 5 ) as well as the strongest limits for charges ≤ e /160, with a minimum intensity of 1.36 × 10 -7 cm -2 s -1 sr -1 at charge e /160.In any rare-event search experiment, understanding background is crucial. Neutrons capable of mimicking dark matter signals are a major background for any dark matter search experiment. A simulation study to estimate the neutron background for an India based dark matter search experiment at Jaduguda Underground Science Laboratory (JUSL) is performed. The experiment at JUSL will be the first phase of a proposed Dark matter search at India-based Neutrino Observatory (DINO). It will be a direct detection experiment with primary aims to search for WIMPs as dark matter candidates. In this thesis, we discuss the methodology of estimating neutron flux at JUSL and report the results. The total neutron flux reaching the laboratory above 1 MeV energy threshold is found to be 5.76(±0.69) × 10 -6 cm -2 s -1 . The impact of neutron background on the sensitivity of the experiment to detect dark matter at JUSL is also discussed. The thesis is organized as follows. Chapter 1 provides a brief introduction to the Lightly Ionizing Particle (LIPs). The analysis to search LIPs in SuperCDMS is briefly outlined in the chapter. This chapter also discusses the importance of neutron background estimates in a dark matter search experiment, more specifically, in the context of a proposed India-based dark matter search experiment at Jaduguda Underground Science Laboratory. In Chapter 2, the SuperCDMS experiment is introduced. In Chapter 3, the framework developed to perform simulations for Lightly Ionizing Particles is presented. In Chapter 4, the LIPs search analysis with the CDMSlite data and the results are discussed. In Chapter 5, the simulation of neutron background and the feasibility of dark-matter search at JUSL is discussed. Finally, conclusions from all the results discussed in this thesis are presented in Chapter 6.

Banik, Samir↗

DOE OSTI2022

Search for lightly ionizing particles in superCDMS and simulation of neutron backgrounds

The Super Cryogenic Dark Matter Search (SuperCDMS) is a direct-detection dark matter search experiment that primarily aims to search for Weakly Interacting Massive Particles (WIMPs) using state-of-the-art solid-state detection technology. During its operation at the Soudan underground laboratory, germanium detectors were operated with high bias voltage mode known as the CDMS low ionization threshold experiment (CDMSlite) to achieve below-keV thresholds. CDMSlite, for being able to measure small energy depositions in detectors, also provides sensitivity to Lightly Ionizing Particles (LIPs) with very small fractional charges. This thesis will discuss an analysis to search LIPs with the data acquired in CDMSlite mode. An important component for LIPs search is the expected energy-deposition distributions for LIPs falling on the CDMSlite detector. In this thesis, a simulation framework to calculate the energy-deposition distributions is developed. This thesis presents first direct-detection limits on the intensity of cosmogenic LIPs with electric charges smaller than e/(3 × 105) as well as the strongest limits for charges ≤ e/160, with a minimum intensity of 1.36 × 10-7 cm-2s-1sr-1 at charge e/160.In any rare-event search experiment, understanding background is crucial. Neutrons capable of mimicking dark matter signals are a major background for any dark matter search experiment. A simulationmore » study to estimate the neutron background for an India based dark matter search experiment at Jaduguda Underground Science Laboratory (JUSL) is performed. The experiment at JUSL will be the first phase of a proposed Dark matter search at India-based Neutrino Observatory (DINO). It will be a direct detection experiment with primary aims to search for WIMPs as dark matter candidates. In this thesis, we discuss the methodology of estimating neutron flux at JUSL and report the results. The total neutron flux reaching the laboratory above 1 MeV energy threshold is found to be 5.76(±0.69) × 10-6 cm-2s-1. The impact of neutron background on the sensitivity of the experiment to detect dark matter at JUSL is also discussed. The thesis is organized as follows. Chapter 1 provides a brief introduction to the Lightly Ionizing Particle (LIPs). The analysis to search LIPs in SuperCDMS is briefly outlined in the chapter. This chapter also discusses the importance of neutron background estimates in a dark matter search experiment, more specifically, in the context of a proposed India-based dark matter search experiment at Jaduguda Underground Science Laboratory. In Chapter 2, the SuperCDMS experiment is introduced. In Chapter 3, the framework developed to perform simulations for Lightly Ionizing Particles is presented. In Chapter 4, the LIPs search analysis with the CDMSlite data and the results are discussed. In Chapter 5, the simulation of neutron background and the feasibility of dark-matter search at JUSL is discussed. Finally, conclusions from all the results discussed in this thesis are presented in Chapter 6.« less

Banik, Samir↗

DOE OSTI2022

Resonance ionization of zirconium

Abstract Measuring the isotopic composition of trace Zr in presolar stardust grains allows us to study the environment of slow neutron-capture nucleosynthesis in asymptotic giant branch stars. Here, we present a newly characterized Zr resonance ionization scheme that can be saturated with state-of-the-art titanium-sapphire lasers and yields a useful yield of (5.4 ± 0.4)%. Resonance ionization is achieved in two steps: after first being excited with a photon at 319.215 nm, neutral Zr atoms are then ionized with a photon at 388.988 nm, where both wavelengths are reported as in vacuum.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

DOE OSTI2025

Active Humidity Control Chamber for Desorption Electrospray Ionization-Mass Spectrometry Imaging Applications

Ambient ionization techniques enable mass spectrometry (MS) to expand into broader experimental contexts, although it is increasingly clear that results are influenced by the environmental conditions at the site of sampling. Desorption electrospray ionization (DESI), in particular, is affected by variations in relative humidity (RH) levels. Here we describe the design, development, and construction of an environmental control chassis that can actively modulate RH within ± 3% of user-defined set points across a broad humidity range (15%–70% RH). Preliminary characterization demonstrated differential analyte responses across a range of set points, with observed enhancement of leucine-enkephalin, sulfadimethoxine (negative mode), and maltose (positive mode) in response to increased humidity. The measurable differences in analyte signals across discrete humidity set points underscore the importance of environmental control in ambient ionization strategies. The humidity control system outlined here can be translated to other DESI platforms, with construction information provided herein.

DESI↗

DOE OSTI2020

Control of electron recollision and molecular nonsequential double ionization

Abstract Intense laser pulses lasting a few optical cycles, are able to ionize molecules via different mechanisms. One such mechanism involves a process whereby within one optical period an electron tunnels away from the molecule, and is then accelerated and driven back as the laser field reverses its direction, colliding with the parent molecule and causing correlated non-sequential double ionization (NSDI). Here we report control over NSDI via spectral-phase pulse shaping of femtosecond laser pulses. The measurements are carried out on ethane molecules using shaped pulses. We find that the shaped pulses can enhance or suppress the yield of dications resulting from electron recollision by factors of 3 to 6. This type of shaped pulses is likely to impact all phenomena stemming from electron recollision processes induced by strong laser fields such as above threshold ionization, high harmonic generation, attosecond pulse generation, and laser-induced electron diffraction.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2020

Resonant x-ray absorption of strong-field-ionized CF 3 Br

We report on an experimental and theoretical study of strong-field laser ionization of CF 3 Br followed by resonant x-ray absorption at the Br K-edge. Distinct 1s -> 4p, 5p Rydberg transitions of Br q+ (q = 1-4) atomic ions are observed and identified with Hartree-Fock-Slater and relativistic configuration interaction calculations. Time-dependent density functional theory and ab initio molecular dynamics calculations were performed to simulate the dissociative ionization process and the molecular orbitals for the q = 1-4 charge states. Measurements were made with both parallel and perpendicular linear polarizations of the laser and x-rays, but dichroism was not observed, indicating negligible alignment by the laser ionization process. This result is explained by calculations on atomic Br and the molecular simulation.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2026

Resonance Ionization Spectroscopy Experiment at Facility for Rare Isotope Beams

This manuscript reports on the commissioning of the Resonance Ionization Spectroscopy Experiment (RISE) at the BEam COoler and LAser spectroscopy (BECOLA) facility at Facility for Rare Isotope Beams (FRIB). The instrument implements the collinear resonance ionization spectroscopy technique for sensitive measurements of isotope shifts and hyperfine structure of short-lived isotopes produced at FRIB. The existing BECOLA beamline was extended to integrate an electrostatic ion-beam bender and an ion detector at ultrahigh vacuum. An injection-seeded titanium-sapphire laser and a multiharmonic pulsed neodymium-doped yttrium aluminum garnet laser were installed to perform resonant excitation and selective ionization. Commissioning tests were performed to demonstrate the capabilities of the instrument by measuring the hyperfine structure of stable 27 Al produced in an offline ion source. The RISE instrument is ready and operational for future studies of short-lived isotopes at FRIB.

Atomic spectra↗

DOE OSTI2023

Modeling the sequential dissociative double ionization of O 2 by ultrashort intense infrared laser pulses

A density matrix approach for sequential double ionization (DM-SDI) of molecules has been developed recently and was applied to the N 2 molecule. In this article, we extended the DM-SDI model to O 2 , which is a more complicated system to model than N 2 , due to its electronic structures and spin-orbit and laser couplings in the manifold of doubly charged states. We obtained a good agreement on the kinetic energy release spectrum of O + + O + from previous experiments. Thanks to the low computational cost of the model, we explored the mechanism behind the ionization and dissociation dynamics as well as the effects of lasers on the spectrum. Furthermore, this work will pave the way to model sequential dissociative double ionization of larger molecules and to probe molecular dynamics by measuring kinetic energy release spectra from this process.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2023

Partial-wave decomposition of the Keldysh ionization amplitude

We present an alternative way of calculating the Keldysh amplitude, i.e., the length-gauge form of the ionization amplitude in the strong-field approximation. The amplitude is evaluated exactly by expanding it in Fourier components and partial waves. Comparisons of the semianalytic model predictions with results of ab initio numerical simulations of the time-dependent Schrödinger equation for the interaction of electrons in short-range potentials with intense laser light yield excellent agreement, for wavelengths from the single photon to the multiphoton to the tunneling regime. Specifically, for ionization from initial states with higher angular momentum quantum number, e.g., p states, a significant improvement over predictions based on the popular saddle-point approximation is found. Furthermore, the current model rate allows for interpretation of the strong-field ionization process in terms of multiphoton absorption pathways and angular momentum selection rules.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2021

Pulse Energy and Pulse Duration Effects in the Ionization and Fragmentation of Iodomethane by Ultraintense Hard X Rays

The interaction of intense femtosecond x-ray pulses with molecules sensitively depends on the interplay between multiple photoabsorptions, Auger decay, charge rearrangement, and nuclear motion. Here, we report on a combined experimental and theoretical study of the ionization and fragmentation of iodomethane (CH 3 I) by ultraintense (~10 19 W/cm 2 ) x-ray pulses at 8.3 keV, demonstrating how these dynamics depend on the x-ray pulse energy and duration. We show that the timing of multiple ionization steps leading to a particular reaction product and, thus, the product’s final kinetic energy, is determined by the pulse duration rather than the pulse energy or intensity. While the overall degree of ionization is mainly defined by the pulse energy, our measurement reveals that the yield of the fragments with the highest charge states is enhanced for short pulse durations, in contrast to earlier observations for atoms and small molecules in the soft x-ray domain. Finally, we attribute this effect to a decreased charge transfer efficiency at larger internuclear separations, which are reached during longer pulses.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Vibrationally resolved ionization cross sections for the ground state and electronically excited states of the hydrogen molecule and its isotopomeres

An existing set of vibrationally resolved ionization cross section for the ground state and the first excited states of the hydrogen molecule, based on the Gryzinski method, is extended by cross sections for the isotopomeres of H{sub 2} (i.e. D{sub 2}, T{sub 2}, HD, HT, and DT), both for non-dissociative and dissociative ionizations. The comparison of cross sections for non-dissociative ionization of H{sub 2} with results obtained by the Molecular Convergent Close-Coupling method gives a very good agreement. The compiled tables give non-dissociative and dissociative cross sections for the ground state and the five energetically lowest electronically excited states of H{sub 2} and its isotopomeres, in each case for the first 9 vibrational levels. Data for all vibrational levels of the excited states is available online.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗