arXiv subjects

David Ayuso

Publications and source records attributed to David Ayuso.

26 records · Page 2Linked to original sources

arXiv2021

Giant chiro-optical response in high harmonic generation

High harmonic generation (HHG) records the ultrafast electronic response of matter to light, encoding key properties of the interrogated quantum system, such as chirality. The first implementation of chiral HHG [Cireasa et al. Nat. Phys. 11, 654 (2015)] relied on the weak electronic response of a medium of randomly oriented chiral molecules to the magnetic component of an elliptically polarized wave, yielding relatively weak chiro-optical signals. Here we show that elliptically polarized light can drive a strong chiral response in chiral molecules via purely electric-dipole interactions -- the magnetic component of the wave does not participate at all. This giant chiro-optical response, which remains hidden in standard HHG experiments, can be mapped into the macroscopic far-field signal using a non-collinear configuration, creating new opportunities for bringing the electric-dipole "revolution" to HHG.

physics.optics↗

arXiv2020

Ultrafast optical rotation for extremely sensitive enantio-discrimination

Sculpting sub-cycle temporal structures of optical waveforms allows one to image and even control electronic clouds in atoms, molecules and solids. Here we show how the transverse spin component arising upon spatial confinement of such optical waveforms enables extremely efficient chiral recognition and control of ultrafast chiral dynamics. When an intense few-cycle, linearly polarized laser pulse is tightly focused into a medium of randomly oriented chiral molecules, the medium generates light which is elliptically polarized, with opposite helicities and opposite rotations of the polarization ellipse in media of opposite handedness. In contrast to conventional optical activity of chiral media, this new nonlinear optical activity is driven by purely electric-dipole interactions and leads to giant enantio-sensitivity in the near VIS-UV domain, where optical instrumentation is readily available. Adding a polarizer turns rotation of the polarization ellipse into highly enantio-sensitive intensity of the nonlinear-optical response. Sub-cycle optical control of the incident light wave enables full control over the enantio-sensitive response. The proposed all-optical method not only enables extremely efficient chiral discrimination, but also ultrafast imaging and control of chiral dynamics with commercially available optical technology.

physics.optics↗

arXiv2020

Polarization of chirality

It has been long recognized that the spatial polarization of the electronic clouds in molecules, and the spatial arrangements of atoms into chiral molecular structures, play crucial roles in physics, chemistry and biology. However, these two fundamental concepts - chirality and polarization - have remained unrelated so far. This work connects them by introducing and exploring the concept of polarization of chirality. We show that, like charge, chirality, or handedness, can be polarized, and that such polarization leads to fundamental consequences, demonstrated here using light. First, we analyze how chirality dipoles and higher-order chirality multipoles manifest in experimental observables. Next, we show how to create chirality-polarized optical fields of alternating handedness in space. Despite being achiral, these racemic space-time light structures interact differently with chiral matter of opposite handedness, and the chirality dipole of light controls and quantifies the strength of the enantio-sensitive response. Using nonlinear interactions, we can make a medium of randomly oriented chiral molecules emit light to the left, or to the right, depending on the molecular handedness and on the chirality dipole of light. The chiral dichroism in emission direction reaches its highest possible value of 200%. Our work opens the field of chirality polarization shaping of light and new opportunities for efficient chiral discrimination and control of chiral and chirality-polarized light and matter on ultrafast time scales.

physics.optics↗

arXiv2019

Locally and globally chiral fields for ultimate control of chiral light matter interaction

Light is one of the most powerful and precise tools allowing us to control, shape and create new phases of matter. In this task, the magnetic component of a light wave has so far played a unique role in defining the wave's helicity, but its influence on the optical response of matter is weak. Chiral molecules offer a typical example where the weakness of magnetic interactions hampers our ability to control the strength of their chiral optical response. It is limited several orders of magnitude below the full potential. Here we introduce freely propagating locally and globally chiral electric fields, which interact with chiral quantum systems extremely efficiently. To demonstrate the degree of control enabled by such fields, we focus on the nonlinear optical response of randomly oriented chiral molecules. We show full control over intensity, polarization and propagation direction of the chiral optical response, enabling its background-free detection. This response can be fully suppressed or enhanced at will depending on the molecular handedness, achieving the ultimate limit in chiral discrimination. Our findings open a way to extremely efficient control of chiral matter and to ultrafast imaging of chiral structure and dynamics in gases, liquids and solids.

physics.optics↗

arXiv2018

Control of attosecond light polarization in two-color bi-circular fields

We develop theoretically and confirm both numerically and experimentally a comprehensive analytical model which describes the propensity rules in the emission of circularly polarized high harmonics by systems driven by two-color counter-rotating fields, a fundamental and its second harmonic. We identify and confirm the three propensity rules responsible for the contrast between the 3N+1 and 3N+2 harmonic lines in the HHG spectra of noble gas atoms. We demonstrate how these rules depend on the laser parameters and how they can be used in the experiment to shape the polarization properties of the emitted attosecond pulses.

physics.atom-ph↗

arXiv2018

Strong-field control and enhancement of chiral response in bi-elliptical high-order harmonic generation: an analytical model

The generation of high-order harmonics in a medium of chiral molecules driven by intense bi-elliptical laser fields can lead to strong chiroptical response in a broad range of harmonic numbers and ellipticities [D. Ayuso et al, J. Phys. B 51, 06LT01 (2018)]. Here we present a comprehensive analytical model that can describe the most relevant features arising in the high-order harmonic spectra of chiral molecules driven by strong bi-elliptical fields. Our model recovers the physical picture underlying chiral high-order harmonic generation based on ultrafast chiral hole motion and identifies the rotationally invariant molecular pseudoscalars responsible for chiral dynamics. Using the chiral molecule propylene oxide as an example, we show that one can control and enhance the chiral response in bi-elliptical high-order harmonic generation by tailoring the driving field, in particular by tuning its frequency, intensity and ellipticity, exploiting a suppression mechanism of achiral background based on the linear Stark effect.

physics.optics↗

arXiv2017

Coherence in Molecular Photoionization

The development of attosecond technology has enabled the real-time observation of coherent electron motion in atoms, molecules and condensed phases. Experimentally, it is now possible to generate laser pulses of durations of only a few tens of attoseconds. These durations are of the order of the revolution period of the first Bohr orbit (150 asec), opening the way to visualize and even control electron dynamics at its natural time scale. This PhD thesis constitutes a theoretical study of fundamental phenomena occurring in gas-phase molecules upon interaction with light. We have investigated ultrafast charge migration in biological molecules initiated by attosecond XUV pulses. In addition, we have studied the high-energy interferences that arise in the vibrationally-resolved photoelectron spectra of small polyatomic molecules. In order to explore these complex phenomena, we have employed numerical methods that describe molecular photoionization by evaluating continuum scattering wave functions, allowing us to compute different observables such as time-dependent electron densities or photoionization cross sections.

physics.chem-ph↗

arXiv2016

Attosecond control of spin polarization in electron-ion recollision driven by intense tailored fields

We show that electrons recolliding with the ionic core upon tunnel ionization of noble gas atoms driven by a strong circularly polarized laser field in combination with a counter-rotating second harmonic are spin polarized and that their degree of polarization depends strongly on the recollision time. Spin polarization arises as a consequence of (1) entanglement between the recolliding electron and the ion, and (2) sensitivity of ionization to the sense of electron rotation in the initial state. We demonstrate that one can engineer the degree of spin polarization as a function of time by tuning the relative intensities of the counter-rotating fields, opening the door for attosecond control of spin-resolved dynamics.

physics.atom-ph↗