Attosecond field-resolved spectroscopy

Optical pulses consist of periodic oscillations of the electromagnetic field with a period between one and three femtoseconds in the optical and near infrared range. Through various light-matter interaction mechanisms, the light can profoundly modify the properties of materials and, at the same time, the interaction can modify the light interacting with the material, inducing a change in its oscillations.

Attosecond technology offers the possibility of characterising the field oscillations of these pulses in time after interaction with a surface, thus providing a new scheme for the non-invasive study of linear and non-linear interaction mechanisms occurring on surfaces and transparent materials.

To this end, we have demonstrated a technique based on the generation of isolated attosecond pulses that allows the complete reconstruction of the field of a few-optical-cycle pulse characterised by a reproducible electric field.

The approach is based on the generation of an isolated attosecond pulse that acts as an ultrashort temporal “gate” with a duration of a few hundred attoseconds. The weak “unknown” field introduces a small perturbation into the generation process, resulting in a modulation of the intensity of the isolated attosecond pulse. By varying the relative delay between the unknown pulse and the attosecond gate, we can measure the full electric field of femtosecond pulses.

The idea behind field-resolved spectroscopy is to fully characterise the changes in the electric field due to the interaction with the material. By comparing the measured changes with those predicted by theoretical models, we aim to probe the ultrafast electronic dynamics of the material with sub-femtosecond resolution.

We are currently implementing this approach for the time-resolved study of the onset of nonlinearities in nanomaterials.