Wavelength scaling of electron collision time in plasma for strong field laser-matter interactions in solids

Understanding self-guiding propagation of laser filaments relies on understanding of the fundamental light-matter interactions, and the optical properties of the plasma. The authors experimentally and theoretically study wavelength scaling of the electron collision time in filament-produced plasma using 1.2-2.3 micrometers and demonstrate an anomalous regime of plasma defocusing in solids. Although the dielectric constant of plasma depends on electron collision time as well as wavelength and plasma density, experimental studies on the electron collision time and its effects on laser-matter interactions are lacking. Here, we report an anomalous regime of laser-matter interactions generated by wavelength dependence (1.2-2.3 mu m) of the electron collision time in plasma for laser filamentation in solids. Our experiments using time-resolved interferometry reveal that electron collision times are small (<1 femtosecond) and decrease as the driver wavelength increases, which creates a previously-unobserved regime of light defocusing in plasma: longer wavelengths have less plasma defocusing. This anomalous plasma defocusing is counterbalanced by light diffraction which is greater at longer wavelengths, resulting in almost constant plasma densities with wavelength. Our wavelength-scaled study suggests that both the plasma density and electron collision time should be systematically investigated for a better understanding of strong field laser-matter interactions in solids.

Automated summary

Understanding self-guiding propagation of laser filaments relies on fundamental light-matter interactions and optical properties of plasma. The authors investigated wavelength scaling of electron collision time in filament-produced plasma, demonstrating an anomalous regime of plasma defocusing in solids. Results suggest that electron collision times decrease with increasing driver wavelength, leading to an unobserved regime of light defocusing in plasma, counterbalanced by light diffraction.