Title: Intensity dependence in nonsequential double ionization of helium
Using the quantitative rescattering model, we simulate the correlated two-electron momentum distributions for nonsequential double ionization of helium by 800 nm laser pulses at intensities in the range of (2 − 15) × 1014W/cm2. The experimentally observed V-shaped structure at high intensities [Phys. Rev. Lett.99,263003(2007)10.1103/PhysRevLett.99.263003] is attributed to the strong forward scattering in laser-induced recollision excitation and the asymmetric momentum distribution of electrons that are tunneling-ionized from the excited states. The final-state electron repulsion also plays an important role in forming the V-shaped structure.
Using the improved quantitative rescattering (QRS) model, we simulate the correlated two-electron momentum distributions (CMD) for nonsequential double ionization (NSDI) of Ar by near-single-cycle laser pulses with a wavelength of 750 nm at an intensity of 2.8 × 1014W/cm2. With the accurate cross sections obtained from fully quantum mechanical calculations for both electron impact excitation and electron impact ionization of Ar+, we unambiguously identify the contributions from recollision direct ionization (RDI) and recollision excitation with subsequent ionization (RESI). Our analysis reveals that RESI constitutes the main contribution to NSDI of Ar under the conditions considered here. The simulated results are directly compared with experimental measurements [Bergueset al.,Nat. Commun.3,813(2012)10.1038/ncomms1807] in which each NSDI event is tagged with the carrier-envelope phase (CEP). It is found that the overall pattern of both the CEP-resolved and the CEP-averaged CMDs measured in experiment are well reproduced by the QRS model, and the cross-shaped structure in the CEP-averaged CMD is attributed to the strong forward scattering of the recolliding electron as well as the depletion effect in tunneling ionization of the electron from an excited state of the parent ion.
Shutova, Mariia; Sinyukov, Alexander M.; Birmingham, Blake; Zhang, Zhenrong; Sokolov, Alexei V.(
, Optics Letters)
Surface-enhanced Raman scattering (SERS) spectroscopy is a popular technique for detecting chemicals in small quantities. Rough metallic surfaces with nanofeatures are some of the most widespread and commercially successful substrates for efficient SERS measurements. A rough metallic surface creates a high-density random distribution of so-called “hot spots” with local optical field enhancement causing Raman signal to increase. In this Letter, we revisit the classic SERS experiment [Surf. Sci.158,229(1985)SUSCAS0039-602810.1016/0039-6028(85)90297-3] with rough metallic surfaces covered by a thin layer of copper phthalocyanine molecules. As a modification to the classic configuration, we apply an adaptive wavefront correction of a laser beam profile. As a result, we demonstrate an increase in brightness of local SERS hot spots and redistribution of Raman signal over the substrate area. We hypothesize that the improvement is due to optimal coupling of the shaped laser beam to the random plasmonic nanoantenna configurations. We show that the proposed adaptive-SERS modification is independent of the exact structure of the surface roughness and topography, works with many rough surfaces, and gives brighter Raman hot spots in comparison with conventional SERS measurements. We prove that the adaptive SERS is a powerful instrument for improving SERS sensitivity.
Hancock, S. W.; Zahedpour, S.; Milchberg, H. M.(
, Optica)
A spatiotemporal optical vortex (STOV) is an intrinsic optical orbital angular momentum (OAM) structure in which the OAM vector is orthogonal to the propagation direction [Optica6,1547(2019)OPTIC82334-253610.1364/OPTICA.6.001547] and the optical phase circulates in space-time. Here, we experimentally and theoretically demonstrate the generation of the second harmonic of a STOV-carrying pulse along with the conservation of STOV-based OAM. Our experiments verify that photons can have intrinsic orbital angular momentum perpendicular to their propagation direction.
AlShafey, Abdallah; Jia, Xu-Yan; Lu, Yuan-Ming; Gong, Shou-Shu; McCaul, Gerard; Bondar, Denys; Randeria, Mohit; Oka, Takashi; Landsman, Alexandra S.(
, Journal of the Optical Society of America B)
The breakdown of a Mott-insulator when subjected to intense laser fields is characterized by the formation of doublon-hole pairs. This breakdown is furthermore evidenced by the production of high harmonics that can be experimentally measured. Here, we present an approach for extracting the doublon-hole correlation length of a Mott insulator. The method is based on a dynamical calculation of the Mott insulator’s rate of charge production in response to an applied strong-field laser pulse. We find that coupling the Mott insulator to a metal drastically increases the correlation length, in support of our recent hypothesis [Phys. Rev. B108,144434(2023)2469-995010.1103/PhysRevB.108.144434] that coupling to a metal enhances the charge fluctuations in the insulator. We confirm our conclusions using density matrix renormalization group (DMRG) calculations. The proposed method can be applied to experimentally measured observables, such as differential reflectivity or the high harmonic generation (HHG) spectrum to extract doublon-hole correlation length.
We proposed the use of relative encircled power as a measure of focusing efficiency [Optica7,252(2020)OPTIC82334-253610.1364/OPTICA.388697]. The comment [Optica8,1009(2021)OPTIC82334-253610.1364/OPTICA.416017] has raised useful questions, which we address briefly here and provide some clarifications.
Chen, Zhangjin, Wen, Hua, Liu, Fang, Morishita, Toru, Zatsarinny, Oleg, and Bartschat, Klaus.
"Intensity dependence in nonsequential double ionization of helium". Optics Express 28 (5). Country unknown/Code not available: Optical Society of America. https://doi.org/10.1364/OE.386971.https://par.nsf.gov/biblio/10135457.
@article{osti_10135457,
place = {Country unknown/Code not available},
title = {Intensity dependence in nonsequential double ionization of helium},
url = {https://par.nsf.gov/biblio/10135457},
DOI = {10.1364/OE.386971},
abstractNote = {Using the quantitative rescattering model, we simulate the correlated two-electron momentum distributions for nonsequential double ionization of helium by 800 nm laser pulses at intensities in the range of (2 − 15) × 1014W/cm2. The experimentally observed V-shaped structure at high intensities [Phys. Rev. Lett.99,263003(2007)10.1103/PhysRevLett.99.263003] is attributed to the strong forward scattering in laser-induced recollision excitation and the asymmetric momentum distribution of electrons that are tunneling-ionized from the excited states. The final-state electron repulsion also plays an important role in forming the V-shaped structure.},
journal = {Optics Express},
volume = {28},
number = {5},
publisher = {Optical Society of America},
author = {Chen, Zhangjin and Wen, Hua and Liu, Fang and Morishita, Toru and Zatsarinny, Oleg and Bartschat, Klaus},
}
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