High energy redshifted and enhanced spectral broadening by molecular alignment

Abstract

We demonstrate an efficient approach for enhancing the spectral broadening of long laser pulses and for efficient frequency redshifting by exploiting the intrinsic temporal properties of molecular alignment inside a gas-filled hollow-core fiber (HCF). We find that laser-induced alignment with durations comparable to the characteristic rotational time scale T R o t A l i g n enhances the efficiency of redshifted spectral broadening compared to noble gases. The applicability of this approach to Yb lasers with (few hundred femtoseconds) long pulse duration is illustrated, for which efficient broadening based on conventional Kerr nonlinearity is challenging to achieve. Furthermore, this approach proposes a practical solution for high energy broadband long-wavelength light sources, and it is attractive for many strong field applications.

Raman Red-shift Compressor: A Simple Approach for Scaling the High Harmonic Generation Cut-off

“…Various approaches based on SRS have been reported in gas cells, [26,27] hollow-core photonic crystal fibers, [28,29] and large-diameter hollow-core fibers (HCF). [22,23,[30][31][32] Particularly, in the study by Safaei et al [32] , we describe a new regime of nonlinear propagation in HCFs that derives from the spatiotemporal nonlinear Raman enhancement observed with subpicosecond driver pulses. This mechanism allows for scaling the peak power by producing broadband, self-frequency shifted solitons driven by subpicosecond pulses.…”

High-energy few-cycle pulses: post-compression techniques

“…On the one hand this slow nonlinearity can be much larger than the instantaneous Kerr-effect which makes it suitable to the compression of low peak-power pulses, on the other hand the input pulse duration needs to be sufficiently long to experience the Raman-effect (>100 fs). A further advantage of many molecular gases against atomic species is that the proportion between nonlinearity and ionization potential is often better than in atomic gases which results in larger spectral broadening capacity [171,172]. Furthermore, the spectral broadening and chirp can be greatly optimized by proper matching of the input pulse duration to the time constant of the delayed nonlinearity (or find a proper molecule for the input pulses), as it was shown in a recent publication of J.E.…”

Raman Red‐Shift Compressor: A Simple Approach for Scaling the High Harmonic Generation Cut‐Off

“…Various approaches based on SRS have been reported in gas cells, [ 26,27 ] hollow‐core photonic crystal fibers, [ 28,29 ] and large‐diameter hollow‐core fibers (HCF). [ 22,23,30–32 ] Particularly, in the study by Safaei et al [ 32 ] , we describe a new regime of nonlinear propagation in HCFs that derives from the spatiotemporal nonlinear Raman enhancement observed with subpicosecond driver pulses. This mechanism allows for scaling the peak power by producing broadband, self‐frequency shifted solitons driven by subpicosecond pulses.…”