Cross compression of light bullets by two-color cofilamentation

The cofilamentation of two ultrashort laser pulses at 800 and $400\mathrm{nm}$ in argon is numerically shown to counteract their temporal splitting. The output pulses are as short as 15 and $6.5\mathrm{fs}$, respectively, without any postprocess compression or stringent alignment. The simultaneous generation of two sub-millijoule (160 and $15\mu \mathrm{J}$, respectively) sub-six-cycle pulses at $\omega$ and $2\omega$ is of particular interest for attosecond science.

Figure 1

(Color online) Quadratic radii of 800 (a) and 400 (b) nm pulses as a function of propagation distance for both stand-alone propagation and cofilamentation. When the two pulses copropagate, a second focusing cycle is observed at $z=102\mathrm{cm}$. Correspondingly, the intensity of 800 (c) [400 (d)] nm increases at $z=0.93$ $\left(1\right)\mathrm{m}$ as B (R) experiences filamentation due to the cross-Kerr-focusing.

Figure 2

(Color online) Temporal intensity (solid line) and phase (dashed line) of the 400 (a) and 800 (b) nm pulses after $150\mathrm{cm}$ propagation, in the case of cofilamentation. Independent propagation is displayed in (c) and (d).

Figure 3

(Color online) Spectrum around $400\mathrm{nm}$. Cofilamentation drastically enhances the spectral broadening through XPM.

Figure 4

(Color online) Temporal shape of $\mathbf{B}$ (a) and $\mathbf{R}$ (b) as a function of the distance when the two pulses copropagate. The durations of the two pulses [full width at half maximum (FWHM)] remain stable over more than $20\mathrm{cm}$ from $z=1.3\text{to}1.5\mathrm{m}$. Note that the walkoff between the two pulses delays $\mathbf{B}$ in the $\mathbf{R}$ frame.

Figure 5

(Color online) $\mathbf{B}$ (a) and $\mathbf{R}$ (b) FWHM duration and contrast ratio (c), (d) after the cofilamentation $(z=150\mathrm{cm})$. Positive delays correspond to the situation where $\mathbf{R}$ reaches the focal region $(z=1\mathrm{m})$ before $\mathbf{B}$.