Periodic Reporting for period 1 - STREDCH (Structured electric-dipole-based chirality)
Période du rapport: 2021-04-01 au 2023-03-31
The rapid development of light sources such as pulsed lasers brings new and largely unexplored possibilities for the manipulation of atoms and molecules with light. The combination of high intensity and controlled polarization found in new light sources is particularly promising for the manipulation of chiral molecules. These are molecules which, like hands, can have a left- and a right-handed version. The building blocks of biological systems (amino acids and sugars) are chiral. Thus, understanding how chiral molecules interact with light has direct consequences for society, particularly in the pharmaceutical and agrochemical sectors. Moreover, molecular chirality has also been recognized as a very useful resource in nanotechnology, e.g. in the construction of molecular machines. This project aims to explore the possibilities provided by new light sources to manipulate chiral molecules.
Light is made up of a magnetic and an electric component. The electric component interacts much more strongly with molecules than the magnetic component. Until recently, due to limitations in both light sources and detectors, the fundamental phenomena relevant for the manipulation of chiral molecules using light relied on the magnetic interaction. This results in hard restrictions in our ability to manipulate chiral molecules because magnetic interactions are weak. Recently, thanks to the development of new light sources and detectors, ways to manipulate chiral molecules relying only on the electric interaction have been found. These are much more effective and have great potential for applications in the chemical industry. However, they remain largely unexplored. This project aims to explore and find new ways to manipulate chiral molecules by relying only on the electric interaction between light and molecules. The project is of a theoretical character but takes current experimental capabilities into account.
As a result of this project, we found several new phenomena occurring upon interaction between intense light and chiral molecules that rely only on electric interactions. We also contributed to the formulation of a theoretical framework appropriate for the description of this type of interaction. We also contributed to understanding the connection between the different phenomena of this type that have emerged in the last few years.
Light is made up of a magnetic and an electric component. The electric component interacts much more strongly with molecules than the magnetic component. Until recently, due to limitations in both light sources and detectors, the fundamental phenomena relevant for the manipulation of chiral molecules using light relied on the magnetic interaction. This results in hard restrictions in our ability to manipulate chiral molecules because magnetic interactions are weak. Recently, thanks to the development of new light sources and detectors, ways to manipulate chiral molecules relying only on the electric interaction have been found. These are much more effective and have great potential for applications in the chemical industry. However, they remain largely unexplored. This project aims to explore and find new ways to manipulate chiral molecules by relying only on the electric interaction between light and molecules. The project is of a theoretical character but takes current experimental capabilities into account.
As a result of this project, we found several new phenomena occurring upon interaction between intense light and chiral molecules that rely only on electric interactions. We also contributed to the formulation of a theoretical framework appropriate for the description of this type of interaction. We also contributed to understanding the connection between the different phenomena of this type that have emerged in the last few years.
The work and main results of this project resulted in 8 peer reviewed publications (1 still in review), 13 oral contributions and 2 posters in scientific conferences, and 4 seminars. The work and main results were the following:
We found that the electric-dipole interaction of randomly oriented chiral molecules with few-cycle, linearly polarized, intense, and very tightly focused IR pulses results in the production of elliptically polarized harmonic radiation encoding the molecular chirality. This phenomenon relies on the emergence of spatially structured elliptical polarization (transverse photon spin) in the focus of the laser and on the overlap of the harmonics due to the large bandwidth of the driving field.
We explored the electric-dipole interaction between bichromatic (fundamental and second harmonic) fields linearly polarized perpendicular to each other and randomly oriented chiral molecules in the context of photoelectron angular distributions in multiphoton processes. We found selection rules for the types of contributions that can emerge in the photoelectron angular distribution in terms of whether those contributions are enantio-sensitive (sensitive to molecular handedness) or dichroic (sensitive to a change in the relative phase between the two colors) and provides analytic formulas for representative cases. We showed that unlike in monochromatic fields, in bichromatic fields the enantio-sensitivity and dichroism of the molecular response do not necessarily appear together. We found that there are signals which record enantio-sensitivity but are completely independent of the relative phase and thus of the instantaneous ellipticity of the field.
We developed an analytical model for the study of strong-field ionization of chiral molecules with circularly polarized light at the level of the electric-dipole approximation and formulated propensity rules for the direction of the resulting asymmetry in the photoelectron angular distribution.
We wrote a contextualized overview and perspective about current research on the topic of ultrafast dynamics in chiral molecules that provides connections between the different phenomena emerging in this field.
We developed an alternative analytical formulation for the photoelectron angular distributions resulting from photoionization of isotropic molecular samples (with an emphasis on chiral samples) subject to arbitrary polarizations (multiple colors and multiple directions) of the electric field at the level of the electric-dipole approximation. This formulation provides selection rules for the enantio-sensitivity of the coefficients describing the photoelectron angular distribution depending on the multiphoton pathways involved, allows interpretation of the photoelectron angular distribution in terms of the vector field defined by the photoionization dipoles, and facilitates understanding how the field polarization couples to the molecular tensors in complex situations such as the multicolor 3D polarizations emerging in locally chiral light.
We explored how molecular chirality influences the phase of the harmonic spectrum of randomly oriented chiral molecules driven by a pair of intense, linearly polarized, non-collinear IR beams.
We found that chirality is imprinted in the topology of the phase structure of the photoelectron emitted in strong field ionization with a linearly polarized, few-cycle, IR pulse.
We explored the emergence of mathematical structures in the photoionization of chiral molecules that are reminiscent to those related to the geometric phases (also known as Pancharatnam-Berry phases) found in many other contexts. We showed that resonantly enhanced two-photon ionization of randomly oriented chiral molecules with a linear pump and a circular probe results in the enantio-selective orientation of the ions, which offers new alternatives for the spatial separation of molecular enantiomers.
We found that the electric-dipole interaction of randomly oriented chiral molecules with few-cycle, linearly polarized, intense, and very tightly focused IR pulses results in the production of elliptically polarized harmonic radiation encoding the molecular chirality. This phenomenon relies on the emergence of spatially structured elliptical polarization (transverse photon spin) in the focus of the laser and on the overlap of the harmonics due to the large bandwidth of the driving field.
We explored the electric-dipole interaction between bichromatic (fundamental and second harmonic) fields linearly polarized perpendicular to each other and randomly oriented chiral molecules in the context of photoelectron angular distributions in multiphoton processes. We found selection rules for the types of contributions that can emerge in the photoelectron angular distribution in terms of whether those contributions are enantio-sensitive (sensitive to molecular handedness) or dichroic (sensitive to a change in the relative phase between the two colors) and provides analytic formulas for representative cases. We showed that unlike in monochromatic fields, in bichromatic fields the enantio-sensitivity and dichroism of the molecular response do not necessarily appear together. We found that there are signals which record enantio-sensitivity but are completely independent of the relative phase and thus of the instantaneous ellipticity of the field.
We developed an analytical model for the study of strong-field ionization of chiral molecules with circularly polarized light at the level of the electric-dipole approximation and formulated propensity rules for the direction of the resulting asymmetry in the photoelectron angular distribution.
We wrote a contextualized overview and perspective about current research on the topic of ultrafast dynamics in chiral molecules that provides connections between the different phenomena emerging in this field.
We developed an alternative analytical formulation for the photoelectron angular distributions resulting from photoionization of isotropic molecular samples (with an emphasis on chiral samples) subject to arbitrary polarizations (multiple colors and multiple directions) of the electric field at the level of the electric-dipole approximation. This formulation provides selection rules for the enantio-sensitivity of the coefficients describing the photoelectron angular distribution depending on the multiphoton pathways involved, allows interpretation of the photoelectron angular distribution in terms of the vector field defined by the photoionization dipoles, and facilitates understanding how the field polarization couples to the molecular tensors in complex situations such as the multicolor 3D polarizations emerging in locally chiral light.
We explored how molecular chirality influences the phase of the harmonic spectrum of randomly oriented chiral molecules driven by a pair of intense, linearly polarized, non-collinear IR beams.
We found that chirality is imprinted in the topology of the phase structure of the photoelectron emitted in strong field ionization with a linearly polarized, few-cycle, IR pulse.
We explored the emergence of mathematical structures in the photoionization of chiral molecules that are reminiscent to those related to the geometric phases (also known as Pancharatnam-Berry phases) found in many other contexts. We showed that resonantly enhanced two-photon ionization of randomly oriented chiral molecules with a linear pump and a circular probe results in the enantio-selective orientation of the ions, which offers new alternatives for the spatial separation of molecular enantiomers.
All the progress reported in the previous section goes beyond the state of the art.
Regarding impact, the manipulation of chiral molecules is essential for today’s chemical industry particularly in the pharmaceutical and agrochemical sectors, both of fundamental importance, and in today’s nanotechnology landscape, where chirality is becoming an increasingly attractive resource. The results of this project uncover fundamental phenomena occurring upon interaction between light and chiral molecules and in this way provide fundamentally new alternatives to approach the manipulation of chiral molecules. This is an essential initial step towards exploiting modern light sources for applications in the chemical industry and in nanotechnology. Furthermore, the scientific results of this project provide a fertile ground for further research on this topic and push forward the scientific and technological development in the EU.
Regarding impact, the manipulation of chiral molecules is essential for today’s chemical industry particularly in the pharmaceutical and agrochemical sectors, both of fundamental importance, and in today’s nanotechnology landscape, where chirality is becoming an increasingly attractive resource. The results of this project uncover fundamental phenomena occurring upon interaction between light and chiral molecules and in this way provide fundamentally new alternatives to approach the manipulation of chiral molecules. This is an essential initial step towards exploiting modern light sources for applications in the chemical industry and in nanotechnology. Furthermore, the scientific results of this project provide a fertile ground for further research on this topic and push forward the scientific and technological development in the EU.