Infrared attosecond field transients and UV to IR few-femtosecond pulses generated by high-energy soliton self-compression

Infrared femtosecond laser pulses are important tools both in strong-field physics, driving x-ray high-harmonic generation, and as the basis for widely tunable, if inefficient, ultrafast sources in the visible and ultraviolet. Although anomalous material dispersion simplifies compression to few-cycle pulses, attosecond pulses in the infrared have remained out of reach. We demonstrate soliton self-compression of 1800-nm laser pulses in hollow capillary fibers to subcycle envelope duration (2 fs) with 27-GW peak power, corresponding to attosecond field transients. In the same system, we generate wavelength-tunable few-femtosecond pulses from the ultraviolet (300 nm) to the infrared (740 nm) with energy up to $25\mu \mathrm{J}$ and efficiency up to 12%, and experimentally characterize the generation dynamics in the time-frequency domain. A compact second stage generates multi-microjoule pulses from 210 to 700 nm using less than $200\mu \mathrm{J}$ of input energy. Our results significantly expand the toolkit available to ultrafast science.

Figure 1

Self-compression to infrared attosecond pulses. Laser pulses at 1800-nm central wavelength with a duration of 30 fs at FWHM are coupled into a 2.5-m-long gas-filled HCF with an inner diameter of $450\mu \mathrm{m}$. In the HCF, the combination of anomalous dispersion arising from the waveguide and positive nonlinearity provided by the gas leads to self-compression of the pulses. With an argon pressure of 470 mbar and an initial pulse energy of $289\mu \mathrm{J}$, the pulse at the HCF exit has an envelope duration of 2 fs at FWHM (a), which corresponds to an 840-as field transient (b). The spectrum of this pulse extends from the ultraviolet (400 nm) to the midinfrared (2550 nm) (c).

Figure 2

Measured dynamics of the self-compression process. (a) Reconstructed pulse profiles at the exit of the $450\text{−}\mu \mathrm{m}$ HCF when filled with 830 mbar of argon as measured using TDP. The first line shows the input pulse (measured with the HCF evacuated) and each subsequent line shows the pulse profile when the HCF is pumped with the energy indicated. Each pulse profile is normalized to its peak. The labels give the FWHM duration of the pulses. (b) Power spectrum of the pulses presented in (a). (c) Output power spectrum as a function of input energy for the same conditions on a logarithmic color scale. The horizontal dotted line marks the point of maximal self-compression, corresponding to the 2.2-fs pulse shown in (a). The vertical dashed line marks the zero-dispersion wavelength.

Figure 3

Generation of tunable resonant dispersive waves from the ultraviolet to near infrared. (a) RDW spectra generated in the first HCF with $450\text{−}\mu \mathrm{m}$ core diameter. Each spectrum is normalized to the peak in the wavelength region shown. The argon pressure required for the generation ranges from 255 mbar (shortest wavelength) to 1330 mbar (longest wavelength). (b) RDW spectra generated in the second HCF ($200\text{−}\mu \mathrm{m}$ core diameter) when driven with 16-fs pulses generated in the first HCF. The pressure varies from 470 mbar (shortest wavelength) to 7000 mbar (longest wavelength).

Figure 4

Performance of the tunable ultraviolet to infrared frequency conversion: (a, b) energy, (c, d) conversion efficiency, and (e, f) FTL duration of the RDWs shown in Fig. 3.

Figure 5

Time-frequency measurements of self-compression and RDW emission. Each column presents the spectrogram obtained of the pulse exiting the HCF, reconstructed from the TDP measurements through numerical back-propagation. The driving pulse energy is indicated above each spectrogram. The argon pressure was 830 mbar. The gate used was Gaussian with a FWHM of 10 fs. The color scale for each plot is normalized to the peak.