HHG Spectroscopy in solids

High harmonic generation (HHG) in atoms and molecules has been studied for several years. Recently, this phenomenon was observed also in the condensed matter phase, revealing unprecedented characteristics compared with the atomic and molecular cases. This discovery allowed the implementation of  new kinds of spectroscopies for materials science.











High-order harmonic spectroscopy in solids represents a powerful tool to explore the interaction between condensed matter and strong laser field, aiming to constitute an all-optical method to characterize materials, as well as to build new optoelectronic devices able to operate even in the petahertz regime. Additionally, because of this strong interaction, it is possible to study out-of-equilibrium properties of solids and peculiar quantum effects in condensed matter, such as Berry phase effects and Weyl Fermions.

To trigger the HHG process, we use strong Mid-Infrared pulses generated by a high-energy optical parametric amplifier. When such pulses illuminate the solid-state sample, the electrons start to oscillate inside the crystal in a sub-cycle time scale. These extremely fast oscillations correspond to highly non-linear currents that generate the high harmonic field.

Our research aims at the investigation of these processes on their natural time scale. To accomplish this we developed a 2 stages Mid-Infrared optical parametric amplifier capable to produce few-cycle pulses. Thanks to our setup we can detect harmonics from the NIR to the UV range for different crystal orientations, and with full characterization of the harmonic polarization state.

We are currently interested in different samples to investigate:

  • Bulk semiconductors: They are the building block of nowadays electronics. Having control over the ultrafast current seems to be promising for new optoelectronic devices.
  • TMDs: Transition metal dichalcogenides are 2D materials characterized by a transition metal linked to two chalcogen atoms of the same species. These novel materials present distinctive properties, such as giant magnetoresistance, Weyl fermions and incredible ability in absorbing light.   The possible applications for these materials are countless, spanning from novel solar cells and new sensing devices.



  • Dr. Angel Rubio (MPI)
  • Dr. Andrea Marini (CNR-ISM)
  • Dr. Giovanni Isella (Polimi)
  • Dr. Alessandro Molle (IMM)


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