Few-Cycle Light Bullets Created by Femtosecond Filaments

We report a generic mechanism of light bullet formation during the filamentation of femtosecond pulses. This mechanism is tested for gaseous and dense media. It allows the production of robust, sub-10 fs structures of light with no post-compression stage. By coupling an infrared pump with a seed beam, tunable pulses with durations down to a few femtoseconds can be generated by parametric processes.

Figure 1

(a) Peak intensity (solid line, left axis) and peak electron density (dashed line, right axis) of a $150\mu \mathrm{m}$-waisted, 25 fs Gaussian pulse propagating in argon at critical power for ${\lambda }_0=800\mathrm{nm}$ and $p=0.5\mathrm{atm}$. (b) On-axis temporal profiles versus propagation distance. (c)–(e) Same for 800 nm, 25 fs Gaussian pulses with 1.2 critical power in silica at (c) ${\lambda }_0=800\mathrm{nm}$, $w_0=4\mu \mathrm{m}$, (d) ${\lambda }_0=1275\mathrm{nm}$, $w_0=7\mu \mathrm{m}$, and (e) ${\lambda }_0=1550\mathrm{nm}$, $w_0=9.6\mu \mathrm{m}$.

Figure 2

(a) Same as Fig. 1b, but with a copropagating $\sim 13\mu \mathrm{J}$, 50 fs seed pulse at 1500 nm. Corresponding spectra at (b) $z=0.1\mathrm{m}$, (c) $z=0.15\mathrm{m}$, and (d) $z=0.5\mathrm{m}$. The dashed line in (d) shows the spectrum without the seed pulse (see Fig. 1). XFROG traces of (e) the pump pulse and (f) the 4WM pulse at $z=0.35\mathrm{m}$. Different color scales were used to improve visibility in (f).

Figure 3

Intensity distribution of (a) seed and (b) 4WM pulses at $z=0.15\mathrm{m}$. The spectral filter is (a) $\lambda >1040\mathrm{nm}$ and (b) $450<\lambda <650\mathrm{nm}$, respectively. (c),(d) Same at the distance $z=0.25\mathrm{m}$. Energy in the 4WM spectral region (d) is $\sim 6\mu \mathrm{J}$; FWHM pulse duration is 5.5 fs.

Figure 4

On-axis spectra and normalized temporal profiles for THG in the wavelength window $210<\lambda <375\mathrm{nm}$: (a),(b) without the seed pulse at $z=0.2\mathrm{m}$ and (c),(d) with the seed at $z=0.25\mathrm{m}$. Shortest FWHM durations are pointed out.