Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session M04: FOCUS: Chiral Light and Chiral ResponseFocus Live
|
Hide Abstracts |
Sponsoring Units: DLS Chair: Loren Greenman, Kansas State University Room: D137-138 |
Thursday, June 4, 2020 8:00AM - 8:30AM Live |
M04.00001: Multiphoton ionization schemes using bicircular laser pulses Invited Speaker: Nicolas Douguet The new generation of light sources has allowed us to access detailed information on atomic and molecular ionization events. Dichroic phenomena in photoionization, i.e., the different response of a system to changes of the polarization state of the incoming light, have shown a high sensitivity to the dynamics of the underlying processes. In this talk, I will present a variety of multiphoton ionization schemes using bicircular light and describe their intrinsic characteristics. First, I will show that circularly polarized bichromatic XUV radiation, as for instance produced by free-electron lasers (FELs), can be used to control the direction of photoelectron emission. The cases of H and Ne will be studied for co- and counter-rotating bichromatic light, as well as for a mixture of linear and circular light. Circular dichroism (CD) will then be considered in order to investigate dichroic properties of electronic systems and chiral matter in general. Using XUV circular light, an atom can be prepared in a polarized resonant state, and an optical field, co- or counter-rotating with the XUV light, can subsequently ionize the oriented atom through a multiphoton process. We will consider two recent CD experiments on He$^+$ and Li atoms, and investigate the origin of the strong CD in both systems. For He$^+$, the variation of the CD over a wide range of IR intensity will be analyzed for the cases of overlapping and non-overlapping XUV and IR fields. Circularly-polarized high XUV harmonics can also be employed in the circular holographic ionization-phase meter (CHIP) method, a new RABBITT-like attosecond spectroscopic technique to retrieve, from a single time-delay measurement, the phase of photoemission amplitudes by angularly resolved photoelectron detection. We will focus on resonant states in He, and the effects of the pulse duration and intensity will be analyzed. Finally, I will present some of our recent advances to describe photoionization schemes involving simple chiral molecules, using accurate multi-electron calculations in the single-electron continuum obtained via the time-dependent perturbative Complex Kohn (TDPT-CK) method. [Preview Abstract] |
Thursday, June 4, 2020 8:30AM - 8:42AM Live |
M04.00002: Sub-Cycle Gating of Optical Chirality in the Photoionization of Chiral Molecules Etienne Bloch, Shaked Rozen, Antoine Comby, Sandra Beauvarlet, Dominique Descamps, Baptiste Fabre, Stephane Petit, Valerie Blanchet, Bernard Pons, Nirit Dudovich, Yann Mairesse Circularly polarized radiation has been the tool of choice to investigate molecular chirality for decades. The recent progress in attosecond metrology has demonstrated the relevance of sub-cycle shaping laser fields to measure and control ultrafast photoionization processes. Here we ionize chiral molecules using a bilinear bichromatic laser field whose oscillation describes an eight '8' shape, rotating in opposite directions every half cycle. Even if this field has zero net (cycle-averaged) chirality, it produces strong asymmetries in the photoelectron angular distributions relative to the laser propagation direction which reverse with molecular handedness and are opposite in the upper and lower hemispheres [1-2]. Measuring the 3D photoelectron momentum distributions reveals the existence of fringe patterns, which are the signature of sub-cycle interferences in the strong field ionization. This holographic imaging provides a unique insight into the dynamical aspect of chiroptical response in the attosecond electron scattering process. [1] Demekhin \textit{et al.}, Phys. Rev. Lett. \textbf{121}, 253201 (2018) [2] Rozen \textit{et al.}, Phys. Rev. X \textbf{9}, 031004 (2019) [Preview Abstract] |
Thursday, June 4, 2020 8:42AM - 8:54AM Live |
M04.00003: Conservation of Torus-Knot Angular Momentum in High-Harmonic Generation Driven by Fields with Spin-Orbit Mixing Emilio Pisanty, Carlos Hernández-García, Laura Rego, Antonio Picón, Julio San Román, Gerard J. Machado, Verónica Vicuña-Hernández, Alessio Celi, Kevin M. Dorney, Henry C. Kapteyn, Margaret M. Murnane, Juan P. Torres, Luis Plaja, Maciej Lewenstein The fundamental polarization singularities of light are symmetric under coordinated rotations: transformations which rotate the spatial dependence by an angle $\theta$ and the polarization by a fraction $\gamma\theta$ of that angle, as generated by 'mixed' angular momenta of the form $L + \gamma S$. Generically, the coordination parameter $\gamma$ has been thought to be restricted to integer or half-integer values. We show that this constraint is an artifact, which originates from the restriction to monochromatic fields, and that a wider variety of singularities can be obtained using the methods of strong-field physics - in particular, the time-domain view on polychromatic fields. We show that these new optical singularities present novel topologies, and how they can be characterized analytically and experimentally. Finally, we explore how these topologies interact with strong-field drivers, by showing that the generator for the symmetry group of these singularities - a mixed type of 'torus-knot' angular momentum - is conserved in nonlinear optical interactions. 1. Nat. Photon. 13, 569 (2019) 2. Phys. Rev. Lett. 122, 203201 (2019) [Preview Abstract] |
Thursday, June 4, 2020 8:54AM - 9:06AM Live |
M04.00004: Photoelectron circular dichroism amplification by interferometric two-photon transitions R. Esteban Goetz, Christiane Koch, Loren Greenman We present an extension of the RABBITT scheme to enhance the photoelectron circular dichroism (PECD) in rotationally isotropic ensemble of chiral molecules. Different portions of the photoelectron wave packet ionized by a comb of XUV frequencies are constrained to interfere in the presence of an infrared (IR) dressing field. An enhancement of the PECD is achieved for appropriate polarization states of the XUV and IR pulses and short IR pulse durations, while the absence of the latter results in a negligible enhancement. We show that the high degree of PECD is robust to the XUV spectral phase and can be efficiently controlled by varying the time delay between the XUV and IR pulses. We exploit this mechanism in pump-probe spectroscopy and show that chiral effects in the dynamics of electronic current density flows can be mapped to the PECD observable while enhancing the sensitivity of detection. [Preview Abstract] |
Thursday, June 4, 2020 9:06AM - 9:18AM Live |
M04.00005: Circular dichroism in few-photon ionization of excited, polarized, and dressed lithium atoms Nishshanka de Silva, Bishnu Acharya, Kevin Romans, Kyle Foster, Katrina Compton, Cole Rischbieter, Onyx Russ, Santwana Dubey, Daniel Fischer We report on an experiment studying the few-photon ionization of atomic lithium. The experiment consist of three parts: First, an all-optical atom trap to prepare an atomic lithium target cloud at milli-Kelvin temperatures where the atoms can be excited and polarized to the 2p (m$_l$=+1); second, an OPCPA that provides intense (typ. 10$^{12}$W/cm$^2$) femtosecond laser pulses with a bandwidth of about 20nm and a center wavelength that can be tuned between 660 and about 800nm; and third, a cold target recoil ion momentum spectrometer (COLTRIMS) recording the photo-electron and recoil ion momenta. In a first investigation we studied circular dichroism for photon energies close to the lithium 2s-2p or 2p-3s resonances. The dressing of the atoms in the field of the ionizing laser causes Autler-Townes shifts that strongly depend on the polarizations of the excited target atoms and of the laser field. This results in a strong circular dichroism that affects not only the total ionization rate and the photo-electron angular distributions but also the energy of the emitted photons. The measured energy spectra and momentum distributions are in very good agreement with a theoretical model solving the time-dependent Schr{\"o}dinger equation in the single-active electron approximation. [Preview Abstract] |
Thursday, June 4, 2020 9:18AM - 9:30AM On Demand |
M04.00006: Laser induced persistent orientation of chiral molecules: experiment and theory Ilia Tutunnikov, Johaness Floss, Erez Gershnabel, Paul Brumer, Ilya Averbukh, Alexander Milner, Valery Milner Molecular chirality is an omnipresent phenomenon of fundamental significance in physics, chemistry and biology. For this reason, search for novel techniques for enantioselective control, detection and separation of chiral molecules is of particular importance. It has been recently predicted {[}1{]} that laser fields with twisted polarization may induce persistent enantioselective field-free orientation of chiral molecules. Here we report the first experimental observation of this phenomenon {[}2{]} using propylene oxide molecules ($\mathrm{CH_{3}CHCH_{2}O}$, or PPO) spun by an optical centrifuge - a laser pulse, whose linear polarization undergoes an accelerated rotation around its propagation direction. We show that PPO molecules remain oriented on a time scale exceeding the duration of the centrifuge pulse by several orders of magnitude. The demonstrated long-time field-free enantioselective orientation opens new avenues for optical manipulation, discrimination, and, potentially, separation of molecular enantiomers.\\ {[}1{]} Phys. Rev. A \textbf{100}, 043406 (2019) {[}2{]} arXiv:1907.13332 {[}physics.chem-ph{]} [Preview Abstract] |
Thursday, June 4, 2020 9:30AM - 10:00AM |
M04.00007: Single and Multiphoton Ionization of Chiral Molecules Invited Speaker: Reinhard D\"orner We will show how linear, planar and chiral molecules react to circular polarizied light. We will discuss single photon ionizations and ionization and fragmentation in a strong laser field measured with a COLTRIMS Reaction Microscope. We will discuss the following findings: \begin{itemize} \item Circular polarized light leads to chiral electron emission pattern even for achiral species. \item Chirality can be enantioselectively induced in a planar molecules by a femtosecond laser pulse. \item Photoelectron and photoion circular dichroism is enhanced by an order of magnitude whenever at least one momentum vector of one particle is measured. \end{itemize} [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700