Fig. Calculations of the ellipticity dependence of the high-harmonic signal in S-epoxypropane (a) and R-epoxypropane (b) confirm that the chiral-sensitive signal is particularly strong around harmonics 41-43, where the primary (chiral -insensitive) High-harmonic channels XX and AA destructively interfere. For each harmonic, the signal was normalized with its corresponding ellipticity-dependent maximum.

R. Cireasa et al. investigated how the chiral structure of the molecule influences this process. While the released electron is driven by the laser field, the same thing happens with the electron hole. Moreover, the laser-driven hole motion is chiral and enantio-sensitive due to the chiral structure of the molecule. When the returning electron recombines with the hole, the enantio-sensitive nature of the hole motion makes the emitted light enantio-sensitive. As a result, a very small ellipticity of the drive laser field, in the range of about 1%, is sufficient to distinguish between the harmonics emitted by left-handed and right-handed molecules, with signals being 2-3% different.

High-harmonic generation can be regarded as pump-probe spectroscopy. Ionization has the function of pumping and starts the electron-hole dynamics. Recombination serves as a probe that maps the electron-hole dynamics by means of the emitted light. The pump-probe delay is controlled by the vibrations of the laser field which drives the electron. The energy of the returning electron depends on how much time it has spent in the field. Therefore, harmonics with different energies are emitted at different times, allowing an assignment between the harmonic order and the pump-probe delay. In short, the harmonic emission records a film of the recombining system, each harmonic representing a frame of the film. A huge bandwidth of the harmonic spectrum leads to a very high temporal resolution, about 0.1 fs or better. R. Cireasa et al. used this property to reconstruct the chiral component of the hole dynamics from the experimentally measured chiral dichroism with a resolution of 0.1 fs.