Self-Compression of Attosecond High-Order Harmonic Pulses

Self-compression of attosecond high-order harmonic pulses in the harmonic generation medium itself has been demonstrated. The attosecond pulses were generated in an argon-filled gas cell and compressed by exploiting the dispersion characteristics of argon. Since the harmonic generation medium itself was used as the compression medium, continuous chirp control was easily achieved by adjusting the gas pressure. The optimized attosecond pulse was also the most intense, and its duration of 206 as was very close to the transform-limited value of 200 as.

Figure 1

Spectral transmittance (solid line) and GDD (dashed line) of the 40-torr 1-mm-long Ar gas column.

Figure 2

Schematic of the experimental setup. The gas cell designed for high pressure operation is also shown. The 45° mirror, which has a 1-mm diameter hole at the center, is used to facilitate overlapping of the harmonic and the probe beam. They are focused again into the target of the time-of-flight spectrometer by a gold-coated toroidal mirror.

Figure 3

Photoelectron counts from He ionized by high-order harmonics from argon at a gas pressure of 15 torr (rectangles), 30 torr (circles), 40 torr (triangles), and 50 torr (diamonds).

Figure 4

(a) Evolution of the photoelectron spectra with time delay in the cases of argon pressure equal to 15 torr (left) and 40 torr (right). (b) Group delay, $\Delta {\phi }_q/2{\omega }_0$, obtained using the RABITT method, for the different gas pressures (same as in Fig. 3). (c) Reconstructed attosecond pulse profiles. The pressure and the pulse widths in FWHM are shown in parentheses in the legend.