Attosecond Technology: Harmonic generation at mhZ repetition rates


Harmonic generation in solids with direct fiber laser pumping

High harmonic generation in solids presents the possibility for bringing attosecond techniques to semiconductors and a simple source for frequency comb spectroscopy in the vacuum ultraviolet. We generate up to the seventh harmonic of a Tm fiber laser by focusing in silicon or zinc oxide. The harmonics are strong and stable, with no indication of material damage. Calculations show the potential for generating 19th harmonic, 12 eV photons.

Fig. 1. Spectra of the 7th, 5th, and 3rd harmonics of a 1 W thulium fiber laser generated in thin-film silicon and zinc oxide.  Silicon has a 1.1 eV indirect, and 3.5 eV direct bandgap.  Zinc oxide has a 3.3 eV direct bandgap.
Fig. 2. The 7th harmonic signal from zinc oxide and silicon integrated over the spectrum as the pump power is stepped up and back down, with direction indicated by the arrows.  The repeatability in both directions indicates that the sample is not being damaged by the strong pump.

[1] K. F. Lee, X. Ding, T. J. Hammond, M. E. Fermann, G. Vampa, and P. B. Corkum, Optics Letters, 42: 1113–1116. 2017

Attosecond Science at uOttawa and NRC