Abstract

Broadband frequency downconversion of a 90 fs 744 nm Ti:sapphire laser pulse into the mid-infrared (IR) was demonstrated via its filamentation-induced self-frequency shift in air and subsequent intra-pulse difference frequency generation in a ${\rm LiGaS}_2$ crystal. The filamentation of the laser pulse in air provided its continuous spectral broadening to the Stokes wing with spectral humps separated by $\sim{1000}\;{{\rm cm}^{- 1}}$ that was appropriate for the laser pulse difference frequency conversion into the mid-IR. The difference frequency emission spectrum spanned from 8.5 to 13.5 µm at the ${{\rm e}^{- 2}}$ level. The transform limited pulse duration of the mid-IR pulse was 47 fs, which corresponded to a 1.3-cycle laser pulse. Energy conversion efficiency was up to ${{10}^{- 4}}$ and ${{5\cdot10}^{- 4}}$ without and with chirp compensation, respectively.

© 2021 Optical Society of America

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