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Generation of terahertz radiation from ionizing two-color laser pulses in Ar filled metallic hollow waveguides
The generation of THz radiation from ionizing two-color femtosecond pulses propagating in metallic hollow waveguides filled with Ar is numerically studied. We observe a strong reshaping of the low-frequency part of the spectrum. Namely, after several millimeters of propagation the spectrum is extended from hundreds of GHz up to 150 THz. For longer propagation distances, nearly single-cycle near-infrared pulses with wavelengths around 4.5 μm are obtained by appropriate spectral filtering, with an efficiency of up to 0.25 %.
Ultrafast spatio-temporal dynamics of terahertz generation by ionizing two-color femtosecond pulses in gases
We present a combined theoretical and experimental study of spatio-temporal propagation effects in terahertz (THz) generation in gases using two-color ionizing laser pulses. The observed strong broadening of the THz spectra with increasing gas pressure reveals the prominent role of spatio-temporal reshaping and of a plasma-induced blue-shift of the pump pulses in the generation process. Results obtained from (3+1)-dimensional simulations are in good agreement with experimental findings and clarify the mechanisms responsible for THz emission.