Chirality is a ubiquitous fundamental property which is standardly analyzed by chiroptical techniques. These techniques measure the system’s differential response to circularly polarized light, and rely on an interplay of electric- and magnetic-dipole transitions, usually yielding very weak chiral signals. In recent years, several seminal electric-dipole based methods were developed that lead to much larger chiral signals. Additionally, the process of high harmonic generation (HHG) was shown to be chirality-sensitive, leading to large (up to ~10%) femtosecond-resolved chiral signals. Remarkably, the chiral signal in HHG still relies on magnetic-dipole interactions, and the signal is relatively large only due to the non-perturbative nature of the process. Extending HHG to produce an electric-dipole based chiral response could thus open-up many possibilities for exploring ultrafast and weak chirality.

Here, we develop an all-optical HHG-based chiroptical technique that relies solely on electric-dipole interactions, leading to huge ultrafast chiral signals. The method is implemented through non-collinear HHG, where the beams’ properties are specially chosen by symmetry considerations that lead to the emission of background-free chiral signals, i.e. signals emitted only from chiral media. We show that this is a general approach that can also be used to probe other intrinsic properties of the medium, such as the presence of ring-currents. Lastly, we utilize the symmetry description of light in order to define a new measure for light’s chirality within the electric dipole approximation (analogous to the molecular definition), which predicts which electromagnetic fields can be used to detect chiral phenomenon.