Macroscopic Control of High Harmonic Generation

High Harmonic Generation (HHG) is an extreme nonlinear optical process in which up-conversion of tens to hundreds of pump photons give rise to a broad-band coherent radiation of nanometer wavelengths emitted at bursts lasting down to tens of atto-seconds.

I review two different works done in our group related to macroscopic control of HHG.

The first work is a theoretical investigation of interesting phenomenon available when the medium is prepared in an excited state prior to its interaction with the intense laser pulse that drives HHG. We show that temporal quasi-phase-matching is made possible in such a system, a scenario that was proposed theoretically but never observed. Additionally, we show that such a system can lead to a new form of radiation – incoherent HHG, or more accurately – to HHG with a controlled degree of temporal coherence.

The second word I discuss is a realization of an experimental system that can probe and manipulate all-optically the macroscopic properties of the emission. With this system we demonstrate unprecedented degree of control of the spectrum of HHG.