Generation of high-temporal-quality sub-two-cycle pulses by self-cleaning of spatiotemporal solitons in air-plasma channels

The temporal sidelobes of few-cycle pulses seriously restrict their applications in ultrafast science. We propose a unique mechanism that enables the generation of sub-two-cycle pulses with a high temporal quality. A robust spatiotemporal soliton could be formed from pulse self-compression by modulating the dispersion of the air-plasma channel via the adjusted plasma density. The self-cleaning of the spatiotemporal soliton leads to the elimination of sidelobes in the temporal profile of the sub-two-cycle pulse. The required density of the preformed plasma for an arbitrary central wavelength from the near-infrared to midinfrared regime is predicted theoretically and confirmed by ($3\mathrm{D}+1$) simulations.

Figure 1

(a), (c) Peak intensity (solid lines) of the femtosecond pulse and the peak density of electron generated by the femtosecond pulse (dashed lines) as a function of propagation distance, when the 1.5-$\mu \mathrm{m}$ pulse propagates in the (a) air and (c) air-plasma channel with ${\rho }_0=8.8\times {10}^{16}{\mathrm{cm}}^{-3}$. (b), (d) On-axis pulse evolution when propagating in the (b) air and (d) air-plasma channel.

Figure 2

Normalized spatiotemporal intensity evolution for ${\lambda }_0=1.5\mu \mathrm{m}, {\tau }_0=50$ fs, ${\rho }_0=8.8\times {10}^{16}{\mathrm{cm}}^{-3}$. The temporal profiles integrated over a circular region with $200\mu \mathrm{m}$ radius are marked on the graph.

Figure 3

(a) Output pulse profile and (b) spectrum at $z=6\mathrm{m}$ when ${\rho }_0={\rho }_p=8.8\times {10}^{16}{\mathrm{cm}}^{-3}$, and the intensity is integrated over a circular region with $200\mu \mathrm{m}$ radius. (c) The evolution of carrier wavelength ${\lambda }_c$ (solid line) and the pulse duration $\tau$ (dashed line). (d) Output pulses when employing air-plasma channels with ${\rho }_0=0.8{\rho }_p$ (solid line) and ${\rho }_0=1.2{\rho }_p$ (dashed line).

Figure 4

The output pulse duration and filament length as a function of input power. The pulse duration is in the unit of optical cycles, and ${\rho }_0$ is fixed at $8.8\times {10}^{16}{\mathrm{cm}}^{-3}$. The inset shows the output pulse profile when $P_{\mathrm{in}}=3P_{\mathrm{cr}}$.

Figure 5

Input (dashed lines) and output (solid lines) pulse shapes when applying the plasma compression scheme to (a) near-infrared and (b) midinfrared laser pulses. Simulation parameters: (a) ${\lambda }_0=0.8\mu \mathrm{m}, {\rho }_0=2.9\times {10}^{17}{\mathrm{cm}}^{-3}, {\tau }_0=25$ fs; (b) ${\lambda }_0=3\mu \mathrm{m}, {\rho }_0=1.4\times {10}^{16}{\mathrm{cm}}^{-3}, {\tau }_0=80$ fs. The input peak power is $P_{\mathrm{in}}=4P_{\mathrm{cr}}$. The output pulse durations are integrated over circular regions with radius (a) $r_0=100\mu \mathrm{m}$ and (b) $r_0=600\mu \mathrm{m}$. The insets show the normalized spatiotemporal intensity distribution.