Frequency-Tunable Multigigawatt Sub-Half-Cycle Light Pulses from Coupled-State Dynamics of Optical Solitons and Impulsively Driven Molecular Vibrations

Coupling ultrashort optical field waveforms to ultrafast molecular vibrations in an impulsively excited Raman medium is shown to enable the generation of frequency-tunable sub-half-cycle multigigawatt light pulses. In a gas-filled hollow waveguide, this coupled-state dynamics is strongly assisted by soliton effects, which help to suppress temporal stretching of subcycle optical pulses, providing efficient Raman-type impulsive excitation of ultrafast molecular vibrations over large propagation paths.

Figure 1

(a) The spectrum (solid line) and the spectral phase profile (dotted line) of an ultrashort laser pulse transmitted through a hollow waveguide filled with molecular hydrogen. The spectrum of the input pulse is shown by the dashed line. The dash-dotted line presents the wavelength dependence of group-velocity dispersion for the fundamental waveguide mode of the gas-filled hollow waveguide. The input pulse energy is $80\mu \mathrm{J}$; the waveguide length is 30 cm. (b) Intensity envelopes for laser pulses transmitted through 25 cm of the hollow waveguide for different soliton numbers $N$, as indicated next to the curves. (Inset) Temporal envelopes of the input laser pulse (dashed line) and the laser pulse transmitted through 30 cm of the hollow waveguide for the input pulse energy of $1\mu \mathrm{J}$ (dash-dotted line) and $80\mu \mathrm{J}$ (solid line). For all the plots, the input pulse width is 2.1 fs, the inner diameter of the hollow waveguide is $200\mu \mathrm{m}$, and the pressure of molecular hydrogen inside the waveguide is 0.05 atm.

Figure 2

Coupled-state dynamics of a single-cycle soliton and molecular coherence: (a) spectral intensity of the light field as a function of the wavelength and propagation path, (b) field intensity, (c) vibrational, and (d) rotational parts of molecular coherence as functions of the propagation path and retarded time. (e),(f) Dynamics of the light pulse within the initial section of the waveguide (e) with Raman effect switched off and (f) in the presence of the Raman effect. The upper panel of Fig. 2c shows temporal cross sections of the vibrational coherence at $z=20\mathrm{cm}$ (1) and 60 cm (2). The input pulse width is 2.1 fs, the input pulse energy is $80\mu \mathrm{J}$, the inner diameter of the hollow waveguide is $200\mu \mathrm{m}$, and the pressure of molecular hydrogen inside the waveguide is 0.05 atm.