Generation of high harmonics using non-classical light and sampling of few-photons near-infrared waveforms*

High harmonic generation (HHG) and field sampling of ultrashort waveforms are the groundstones of attosecond science. HHG has been used to realize coherent sources in the extreme ultraviolet (XUV) and X-ray regions, study the properties of matter on ultrafast timescales, and generate attosecond pulses. The need to characterize these pulses has driven the development of various techniques to sample the full electric field of light in the XUV and infrared (IR), providing new tools for attosecond metrology [1]. Over the years, high harmonics have been generated in different states of matter(gases, liquids, solids, and plasmas) but always using coherent states of light. Lately, theoretical and experimental works have explored quantum aspects of HHG and predicted that using non-coherent states of light as a driver will yield unique features [2].

Here, I will present our recent work on the generation of high harmonics using a bright squeezed vacuum (BSV), a macroscopic quantum state of light that we generate in a single-spatiotemporal mode and with a photon number distribution covering states from 0 to > 10¹³ photons per pulse. Using this unprecedently bright non-classical state of light, we generate high harmonics from solids and show an enhancement in their yield compared to classical light.

In the second part of the talk, I will present our work on a generalized heterodyne optical sampling technique [3] and show its use to characterize the electric field of near-IR waveforms at 505 KHz with a sensitivity of a few photons per pulse.

[1]  A. Herbst, K. Scheffter, M. M. Bidhendi, M. Kieker, A. Srivastava, & H. Fattahi, Recent advances in petahertz electric field sampling, J. Phys. B: At. Mol. Opt. Phys. 55, 172001 (2022).

[2]  L. Cruz-Rodriguez, D. Dey, A. Freibert, & P. Stammer, Quantum phenomena in attosecond science, Nat Rev Phys 6, 691 (2024).

[3]  D. A. Zimin, V. S. Yakovlev, & N. Karpowicz, Ultra-broadband all-optical sampling of optical waveforms, Science Advances 8, eade1029 (2022).