Abstract
Extreme nonlinear interactions of THz electromagnetic fields with matter are the next frontier in nonlinear optics. However, reaching this frontier in free space is limited by the existing lack of appropriate powerful THz sources. Here, we experimentally demonstrate that two-color filamentation of femtosecond mid-infrared laser pulses at 3.9 μm allows one to generate ultrashort sub-cycle THz pulses with sub-milijoule energy and THz conversion efficiency of 2.36%, resulting in THz field amplitudes above 100 MV cm−1. Our numerical simulations predict that the observed THz yield can be significantly upscaled by further optimizing the experimental setup. Finally, in order to demonstrate the strength of our THz source, we show that the generated THz pulses are powerful enough to induce nonlinear cross-phase modulation in electro-optic crystals. Our work paves the way toward free space extreme nonlinear THz optics using affordable table-top laser systems.
Highlights
Extreme nonlinear interactions of THz electromagnetic fields with matter are the frontier in nonlinear optics
By taking into account that nonlinear propagation plays a major role in filament-based THz sources, recently we performed theoretical investigations and numerical simulations which predict that twocolor filamentation of mid-infrared laser pulses can be a source of single cycle THz pulses with multi-millijoule energies and extremely high THz conversion efficiencies, which are more than two orders of magnitude higher than for 0.8 μm laser pulses[37,38]
The THz conversion efficiency obtained in our experiment is more than two orders of magnitude higher compared to typical values reported for 0.8 μm two-color laser pulses
Summary
Extreme nonlinear interactions of THz electromagnetic fields with matter are the frontier in nonlinear optics. By taking into account that nonlinear propagation plays a major role in filament-based THz sources, recently we performed theoretical investigations and numerical simulations which predict that twocolor filamentation of mid-infrared laser pulses can be a source of single cycle THz pulses with multi-millijoule energies and extremely high THz conversion efficiencies, which are more than two orders of magnitude higher than for 0.8 μm laser pulses[37,38] These results were later confirmed numerically by Nguyen et al.[39] we showed that there is an optimal wavelength for two-color filamentation-induced THz sources: for 3.2 μm laser pulses the THz conversion efficiency reaches its maximum of about 7%40. Our theoretical analysis reveled that the extreme efficiency of mid-infrared two-color filamentation for THz generation is caused by a combination of many factors: strong photocurrents due to larger ponderomotive forces, longer and wider plasma channels, negligible walk-off between the fundamental and second harmonic, additional field symmetry breaking by generated high harmonics[37,38]
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