Science: accurate chirality measurement on the time scale of attosecond

The interaction of chiral light matter has been studied for two centuries, and many methods have been found to identify enantiomers Most of the chiral optical effects are caused by the response of bound electrons Photoionization can produce much stronger chiral signal, which is characterized by the asymmetry of the angular distribution of photoelectrons along the optical propagation axis Photo ionization diagram of two camphor enantiomers (source: Science) an international research team has been able to use attosecond (10 to the minus 18 power seconds) optoelectronic interference technology to accurately detect when electrons pop out of chiral molecules This method is very accurate and can be applied to the quantum theory of ionization of reference molecules, or to the study of ultrafast processes in superconducting chiral nanotubes or spin electronic devices The principle of photoelectron interferometry (source: Science) when light hits a molecule, light can ionize the molecule, resulting in nearly instantaneous emission of electrons Because the electron is so light and the reaction is so fast, it is considered that the experimental measurement cannot be realized because it is too fast But the latest developments in attosecond science have made it possible The ionization of randomly oriented camphor molecules was studied by a team from the centre for intense lasers and Applications (Celia) in France using a special attosecond setting Their experiment revealed a very small time shift between the forward and backward electrons - only seven attoseconds If you switch enantiomers, the delay is reversed As we all know, when the chiral molecules are ionized by circularly polarized light, there is an imbalance between the intensity of electrons emitted in the front and back direction relative to the beam direction The dissymmetry studied by the photoelectron circular dichroism (PECD) is up to a few percent, which is three orders of magnitude larger than the dissymmetry usually encountered in the long established technology This may give PECD greater sensitivity to distinguish left-handed and right-handed molecules However, the comprehensive theoretical understanding of PECD effect is challenging When a bolt is rotated on a nut, the chirality of the thread converts rotation into translation and moves forward or backward according to the direction of rotation The same can happen when the photoionization of chiral molecules is carried out by circularly polarized light It is worth noting that this happens even in randomly oriented chiral molecular jets The realization of the measurement function is attributed to the high stability of the laser source and all optical elements, which enables the accuracy to reach the time resolution of 1 a second Phase decomposition resonance photoionization of camphor (source: Science) researchers have developed a technique that uses the ionization of two phase-locked laser fields to detect differential attosecond delay They work in infrared (800 nm) and ultraviolet (400 nm) wavelengths, and combine linear and circularly polarized femtosecond laser pulses By independently controlling ionization and detecting the chirality of light pulses, scientists can decouple the actual photoelectron delay caused by measurement, which may lead to inaccuracy The angle resolved photoelectron spectroscopy was obtained by collecting photoelectron with imaging spectrometer, and the electron emission delay in different directions was compared The angle resolved time distribution (source: Science) of self ionized photoelectron wave packet provides an important new insight into the mechanism of chiral ionization If the intrinsic orientation light is used for ionization, the intrinsic structural asymmetry of the detected molecule will also lead to the time asymmetry of the photoelectron emission process The experimental complexity of this method may limit its use in conventional analytical applications, because there are simpler methods to determine the chirality of molecules But new findings may support the development of other procedures to identify and quantify enantiomers The high accuracy of the measurement can also be used as a reference tool for the quantum theory of molecular photoionization It can also be extended to a variety of systems to reveal ultrafast symmetry breaks, superconducting chiral nanotubes and chiral spin electronics devices Wigner villedistributions (wvds) autoionization photoelectron wave packet (source: Science) paper link: http://science.sciencemag.org/content/358/6368/1288