Self-Compression of Ultrashort Pulses through Ionization-Induced Spatiotemporal Reshaping

We present the first demonstration of a new mechanism for temporal compression of ultrashort light pulses that operates at high (i.e., ionizing) intensities. By propagating pulses inside a hollow waveguide filled with low-pressure argon gas, we demonstrate a self-compression from 30 to 13 fs, without the need for any external dispersion compensation. Theoretical models show that 3D spatiotemporal reshaping of the pulse due to a combination of ionization-induced spectral broadening, plasma-induced refraction, and guiding in the hollow waveguide are necessary to explain the compression mechanism.

Figure 1

Spectra of pulses emerging from waveguide filled with argon pressures of 4 torr decreasing to 1.1 torr. Ionization induces a spectral blueshift and broadening of the spectrum.

Figure 2

Input and output pulse characteristics at the 4 torr optimum pressure for compression of pulse with an input laser intensity of ${10}^{15}\mathrm{W}{\mathrm{c}\mathrm{m}}^{-2}$. (a) Temporal profile of the input pulse (29 fs) and the final compressed pulse (13.3 fs). (b) Measured spectrum of the compressed pulse, compared with the retrieved spectrum from the FROG data. The excellent agreement confirms the fidelity of the pulse measurement.

Figure 3

Comparison between the experimentally observed and theoretically predicted pulse envelopes as a function of pressure for 0, 2, 4, 6, 8, and 9 torr. (a) Experimentally measured pulse shapes. (b) Theoretically predicted pulse shapes. The pulse compression and pulse splitting behavior are seen both experimentally and theoretically, with excellent qualitative and good quantitative agreement between experiment and model.