Article
Physics, Multidisciplinary
Si-Qi Zhang, Qi Zhen, Zhi-Jie Yang, Jun Zhang, Ai-Hua Liu, Kai-Jun Yuan, Xue-Shen Liu, Jing Guo
Summary: The ultrafast photoionization dynamics of N-2 molecules by x-ray/XUV laser pulses was investigated, showing the appearance and disappearance of molecular photoionization diffraction at different laser wavelengths, as well as changes in the molecular frame photoelectron momentum distributions and angular distributions.
Review
Optics
Paul Hockett, Varun Makhija
Summary: This article outlines and discusses methods for experimental reconstruction of molecular frame photoionization dynamics and related properties, particularly MF photoelectron angular distributions (PADs) and continuum density matrices. General concepts are introduced for non-expert readers, and experimental and theoretical techniques are outlined in depth. A detailed example of numerical reconstruction techniques for matrix-element retrieval from time-domain experimental measurements using rotational-wavepackets is presented, along with a matrix-inversion technique for direct MF-PAD recovery. Ongoing resources for interested researchers, including sample data, reconstruction codes, and literature via online repositories, are also introduced.
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
(2023)
Article
Chemistry, Physical
Yasashri Ranathunga, Temitayo Olowolafe, Emmanuel Orunesajo, Hackim Musah, Suk Kyoung Lee, Wen Li
Summary: We present a straightforward method for achieving three-dimensional ion momentum imaging. This method utilizes two complementary metal-oxide-semiconductor cameras along with a standard microchannel plates/phosphor screen imaging detector. The cameras are synchronized to measure the decay of luminescence generated by ion collisions and extract the time of flight. The time resolution achieved is better than 10 ns, primarily limited by camera jitters, but can reach better than 5 ns resolution when the jitter is minimized.
JOURNAL OF CHEMICAL PHYSICS
(2023)
Article
Instruments & Instrumentation
Chuan Cheng, Goenenc Mogol, Thomas Weinacht, Andrei Nomerotski, Carlos Trallero-Herrero
Summary: In this study, we demonstrate three-dimensional velocity map imaging of low energy electrons using a TPX3CAM. The position and timing information on the camera sensor encode the three-dimensional momentum information [p(x), p(y), p(z)]. By employing a constant fraction discriminator and fast time to digital converter in the camera, we can accurately capture the time information. We showcase the capabilities of our apparatus through above threshold ionization measurements of xenon, which reveal distinct structures in the momentum-resolved photoelectron yield.
REVIEW OF SCIENTIFIC INSTRUMENTS
(2022)
Article
Optics
Dianxiang Ren, Shang Wang, Chao Chen, Xiaokai Li, Xitao Yu, Xinning Zhao, Pan Ma, Chuncheng Wang, Sizuo Luo, Yanjun Chen, Dajun Ding
Summary: The ionization dynamics of aligned N-2 molecules in strong elliptical laser fields have been studied. It was found that the ionization of N-2 strongly depends on the alignment of molecules relative to the polarization ellipse of the laser. The interaction between molecular structure and the laser fields plays an important role in the rotation angles and photoelectron angle distribution of aligned N-2.
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
(2022)
Article
Biology
Liyue Shen, Wei Zhao, Dante Capaldi, John Pauly, Lei Xing
Summary: This study establishes a geometry-informed deep learning framework for ultra-sparse 3D tomographic image reconstruction. The seamless inclusion of geometric priors is shown to be essential for enhancing imaging performance and provides new avenues for data-driven biomedical imaging.
COMPUTERS IN BIOLOGY AND MEDICINE
(2022)
Article
Astronomy & Astrophysics
Poonam Choudhary, Bheemsehan Gurjar, Dipankar Chakrabarti, Asmita Mukherjee
Summary: Gravitational form factors provide information about internal distributions of mass, energy, pressure, and shear. The Druck term is the least understood among all form factors. In this study, the Druck form factor is investigated in a light front quark-diquark model, and the 3D distribution in the Breit frame is evaluated using Abel transformation.
Article
Astronomy & Astrophysics
Julia Yu Panteleeva, Maxim Polyakov
Summary: The study establishes the mathematical equivalence between force distributions in Breit frame and light front, where pressure and shear force distributions in Breit frame can be transformed unambiguously into light front force distributions through Abel transformation. The positivity property of Abel transformation ensures that 2D local stability conditions are satisfied automatically if the corresponding 3D stability conditions are fulfilled.
Article
Physics, Multidisciplinary
Xiaofan Zhang, Xiaomeng Ma
Summary: We theoretically investigate the photoelectron momentum distributions of 1s and 2p(x, y) states of hydrogen by twisted attosecond X waves carrying orbital angular momentum based on first-order perturbation theory. The photoionization spectra as a function of photoelectron energy and emission angle are analyzed respectively. The results indicate that there are interference fringes in the energy spectra and more nodes in the angular distributions. These angular nodes are attributed to both orbital structure and the temporal-spatial structure of X waves. We derive an equation that can quantitatively describe the angular nodes in the photoelectron angular distributions. Our results and analyses indicate that the angular distribution is an important observation for the investigation of the information of both orbitals and X waves.
FRONTIERS IN PHYSICS
(2023)
Article
Optics
Rui-Hua Xu, Ying-Kui Zhao, Yan-Jun Chen, Li-Bin Fu
Summary: By numerically solving the time-dependent Schrodinger equation, we investigated the ionization of helium atoms in different atomic potentials in orthogonally polarized two-color laser fields. We found that long-range atomic potentials lead to asymmetric photoelectron momentum distributions, while short-range potentials result in nearly symmetric structures, with the asymmetry being more pronounced at lower laser intensity and/or shorter laser wavelength. The results may serve as a reference for further analytical studies on strong-field ionization of complex atoms and molecules, considering Coulomb effects for quantitative descriptions.
Article
Environmental Sciences
Shuhang Dong, Zekun Jiao, Liangjiang Zhou, Qiancheng Yan, Qianning Yuan
Summary: With the advancement of airborne synthetic aperture radar (SAR) technology, the reconstruction of 3D SAR point clouds has become a crucial development trend. However, due to measurement errors, environmental interference, radar decoherence, and other noises, the reconstructed tomogram often contains numerous noisy scatterers, making it challenging to obtain high-quality point clouds for further processing and target identification. In this study, we propose a K nearest neighbor comprehensive weighted filtering algorithm, which effectively refines the tomogram by evaluating the filtered point cloud quantitatively using three-dimensional entropy. The algorithm's superiority is demonstrated through qualitative and quantitative analyses using simulated data and actual SAR data.
Article
Instruments & Instrumentation
Chrisy Sparling, Alice Ruget, Jonathan Leach, Dave Townsend
Summary: The inverse Abel transform is widely used in charged particle imaging, but it has limitations due to cylindrical symmetry constraints. This study shows how artificial neural networks can replace the inverse Abel transform and directly reconstruct 2D projections into 3D distributions.
REVIEW OF SCIENTIFIC INSTRUMENTS
(2022)
Article
Optics
Navid Ibtehaj Nizam, Marien Ochoa, Jason T. Smith, Xavier Intes
Summary: This study reports on the potential of using deep learning for image reconstruction in 3D k-space reflectance fluorescence tomography (FT). A modified AUTOMAP architecture and a training methodology using an open-source Monte-Carlo-based simulator are adopted to generate a large dataset. The results indicate that the proposed approach can accurately reconstruct single and multiple fluorescent embeddings in a 3D volume, surpassing traditional approaches, particularly at greater depths.
Article
Computer Science, Information Systems
Dong Han, Zekun Jiao, Liangjiang Zhou, Chibiao Ding, Yirong Wu
Summary: In this study, a tomoSAR 3D reconstruction method based on geometric constraints is proposed to optimize the reconstruction results of building facades. The geometric constraints are extracted by processing and fusing the point density map and height map from the tomoSAR 3D point cloud. By imposing these constraints and using an adaptive iterative shrinkage-thresholding algorithm, an optimized tomoSAR 3D reconstruction result is achieved. Experimental results using measured data from a P-band airborne tomoSAR system demonstrate the superiority of the proposed method over traditional methods without geometric constraints.
SCIENCE CHINA-INFORMATION SCIENCES
(2023)
Article
Optics
Margaret Gregory, Paul Hockett, Albert Stolow, Varun Makhija
Summary: A theory and method for matrix-based reconstruction of molecular frame photoelectron angular distributions from laboratory frame measurements is developed and applied to nonlinear polyatomic molecules. This new technique does not require determination of photoionization matrix elements and allows successful reconstruction of MF photoelectron angular distributions.
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
(2021)
Article
Optics
Juan J. Omiste, Lars Bojer Madsen
Summary: The study highlights the significance of electron correlation effects in the ionization process induced by laser pulses, and shows that circularly and linearly polarized pulses lead to different ionization channels and affect the momentum distribution of photoelectrons.
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
(2021)
Review
Physics, Multidisciplinary
Lars Bojer Madsen
Summary: This paper discusses the interactions between atoms and molecules with intense laser pulses, describing them in terms of velocity gauge, length gauge, or the Kramers-Henneberger frame. It explores the relationships between these forms, particularly focusing on expansions in adiabatic states for solving the time-dependent Schrodinger equation. The discussion highlights the potential attractiveness of these expansions for intense long-wavelength infrared laser pulses.
EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS
(2021)
Article
Optics
J. Maurer, U. Keller
Summary: This article discusses the breakdown of the dipole approximation in strong laser fields and the resulting non-dipole effects on ionization processes. Recent studies have provided more insight into these effects, with advancements in experimental techniques enabling their observation.
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
(2021)
Article
Chemistry, Multidisciplinary
Hiroka Hasegawa, Tiffany Walmsley, Akitaka Matsuda, Toru Morishita, Lars Bojer Madsen, Frank Jensen, Oleg I. Tolstikhin, Akiyoshi Hishikawa
Summary: The dissociative ionization of tetrafluoromethane in intense laser fields has been studied, showing clear asymmetry in the spatial distribution of the produced ions. The asymmetry can be controlled by the shape of the laser pulse, and the C-F bond along the larger amplitude side tends to be broken. Theoretical analysis suggests an enhancement of tunneling ionization in the opposite direction to the observed asymmetric fragment ejection.
FRONTIERS IN CHEMISTRY
(2022)
Article
Multidisciplinary Sciences
Andrew S. Maxwell, Lars Bojer Madsen, Maciej Lewenstein
Summary: The study explores the possibility of orbital angular momentum (OAM) entanglement in attosecond imaging and investigates the entanglement properties of photoelectrons in non-sequential double ionization. Through calculations of logarithmic negativity and entanglement witness, the study reveals the robustness of entanglement to incoherence and the relationship between OAM coherence terms and entanglement measurement. The entanglement of photoelectron pairs with the highest degree of entanglement is quantified for various targets and field parameters. This methodology provides a universal approach to quantify and measure entanglement using OAM, which is well-suited for attosecond processes and can enhance imaging capabilities or generate OAM-entangled electrons.
NATURE COMMUNICATIONS
(2022)
Article
Optics
Mahmoud Abu-samha, Lars Bojer Madsen
Summary: We present theoretical results for intensity-dependent above-threshold ionization (ATI) spectra from oriented OCS molecules probed by intense femtosecond laser pulses with wavelengths of 800 and 400 nm. The calculations were performed using the time-dependent Schrodinger equation within the single-active-electron approximation and including multielectron polarization effects. The results capture some of the experimental findings, in particular when considering the sensitivity of the ATI spectra on the molecular orientation. We identify characteristic features in the ATI spectra which correspond to resonant multiphoton ionization via highly-excited Rydberg states are captured by the theory.
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
(2023)
Article
Materials Science, Multidisciplinary
P. D. Keathley, S. V. B. Jensen, M. Yeung, M. R. Bionta, L. B. Madsen
Summary: We demonstrate the experimental feasibility of time-domain analysis of high harmonic generation (HHG) from solids with subcycle resolution and continuous spectral coverage. Using time-dependent density functional theory, we explore the insights that a time-domain, field-resolved analysis can provide about the underlying extreme nonlinear electron dynamics responsible for HHG in solids. We show that visual analysis of the time-domain fields can reveal the interplay between intra- and interband dynamical processes, providing clear insights even when spectral signatures do not. We also find that field-resolved measurements with subcycle time resolution and broad spectral coverage are essential for a comprehensive understanding of solid-state HHG.
Article
Chemistry, Physical
H. Hasegawa, A. Matsuda, T. Morishita, L. B. Madsen, F. Jensen, O. I. Tolstikhin, A. Hishikawa
Summary: Directional fragment ejection from a tetrahedral molecule CH4 under two-color laser fields has been studied. The H+ fragment, as well as the low kinetic energy components of the Coulomb explosion, preferentially ejects on the larger amplitude side of the laser electric fields. On the other hand, high energy components and the H-2(+) ion show opposite directional ejection.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2023)
Article
Materials Science, Multidisciplinary
Thomas Hansen, Lars Bojer Madsen
Summary: This study investigates high-harmonic generation from doped, correlated materials using the one-dimensional Hubbard model. It finds that doping has little to no effect on the dynamics and spectra for small electron-electron correlation, but has a significant impact for larger correlation. The findings are explained through a quasiparticle-based picture.
Article
Optics
Lars Bojer Madsen
Summary: It has been found that above-threshold-ionization peaks disappear when the kinetic energy associated with the nondipole radiation-pressure-induced photoelectron momentum in the laser propagation direction becomes comparable to the photon energy. However, these peaks can be made to reappear if knowledge of the length and direction of the photoelectron momentum is at hand and an emission-direction-dependent momentum shift is accounted for.
Article
Optics
M. Abu-samha, Lars Bojer Madsen
Summary: This paper revisits the strong-field ionization of aligned O-2, CO2, and CS2 molecules in light of recent advances in the field of strong-field physics. By including the effect of multielectron polarization, the total ionization yields can be reduced and the alignment angle of maximum yields can shift for molecules with large polarizability.
Article
Optics
Thomas Hansen, Simon Vendelbo Bylling Jensen, Lars Bojer Madsen
Summary: Using the Hubbard model, this study investigates the effect of electron-electron correlation on high-order harmonic generation (HHG) in both finite and bulk systems. The results show that finite-size enhancement of the HHG signal is observed, attributed to electrons backscattering off the lattice edges. Furthermore, an enhancement in the high-frequency regime of the HHG spectrum is found with increasing electron-electron correlation.
Article
Optics
Lars Bojer Madsen
Summary: This study investigates the impact of nondipole effects on tunneling ionization in the limit of decreasing laser frequency. The results show the influence of the nondipole term on ionization rate, momentum, and electron dynamics, providing insights into the inclusion of nondipole effects in semiclassical models of strong-field and attosecond physics.
Article
Chemistry, Physical
H. Fujise, M. Uemura, H. Hasegawa, D. Ikeya, A. Matsuda, T. Morishita, L. B. Madsen, F. Jensen, O. Tolstikhin, A. Hishikawa
Summary: The dissociative tunneling ionization of tetrafluoromethane (CF4) in circularly polarized ultrashort intense laser fields has been studied using three-dimensional electron-ion coincidence momentum imaging. It was found that the dissociation occurs efficiently when the laser electric field points from F to C. Additionally, the results also showed a clear dependence on the polarization helicity of the laser fields.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2022)
Article
Optics
Simon Vendelbo Bylling Jensen, Lars Bojer Madsen
Summary: Applying the semiclassical model, we have identified two connected effects in intraband high-order harmonic generation (HHG): propagation time from the point of emission to the point of detection, and beyond-electric-dipole corrections to the light-matter interaction. These effects carry information about dispersion and result in specific features in the spectra, including even-ordered harmonics in systems with space and time-inversion symmetry. They can be measured without interference from the dipole background under certain experimental geometries.
