Generation of Isolated Attosecond Pulses with 20 to 28 Femtosecond Lasers

Isolated attosecond pulses are powerful tools for exploring electron dynamics in matter. So far, such extreme ultraviolet pulses have only been generated using high power, few-cycle lasers, which are very difficult to construct and operate. We propose and demonstrate a technique called generalized double optical gating for generating isolated attosecond pulses with 20 fs lasers from a hollow-core fiber and 28 fs lasers directly from an amplifier. These pulses, generated from argon gas, are measured to be 260 and 148 as by reconstructing the streaked photoelectron spectrograms. This scheme, with a relaxed requirement on laser pulse duration, makes attophysics more accessible to many laboratories that are capable of producing such multicycle laser pulses.

Figure 1

Comparison of laser field components for polarization gating in DOG (a) and GDOG (b). In both (a) and (b), the driving field and gating field are plotted in the solid red line and dashed blue line, respectively, and the ellipticity is plotted in the dash-dotted green line.

Figure 2

(a) GDOG optics consist of a quartz plate (QP1), a Brewster window (BW), a second quartz plate (QP2), and a BBO crystal. (b) Setup for measuring the single attosecond pulses. The Ti:sapphire laser beam was split into two. One beam propagated through the GDOG optics and was focused by a mirror (M) onto the argon gas jet (GJ1) to generate the attosecond pulses. The aluminum filter (F) filtered out the lower high harmonics and the fundamental beam. The XUV beam was focused by the $\mathrm{Mo}/\mathrm{Si}$ mirror in the center of the two-component mirror on the detection neon gas target (GJ2). The other beam for streaking traveled through a lens (L) and was focused by the annular mirror in the two-component mirror onto the detection gas jet. The photoelectron energy was measured by a time-of-flight spectrometer (TOF).

Figure 3

Attosecond XUV pulse generated from argon gas using 20 fs laser pulses. (a) Experimental CRAB trace. (b) Retrieved trace. (c) Retrieved XUV pulse (solid line) and temporal phase (dashed line). The inset shows the temporal profile over 4 cycles on a log scale. (d) Comparison of the measured unstreaked XUV spectrum (blue or dark gray dashed line) and the retrieved XUV spectrum (solid line) accompanied by the retrieved spectral phase (red or gray dashed line). A positive chirp of $7850{\mathrm{as}}^2$ was obtained from the phase.

Figure 4

Attosecond XUV pulse generated from argon gas using 28 fs laser pulses directly from the amplifier. (a) Experimental CRAB trace. (b) Retrieved CRAB trace. (c) Retrieved XUV pulse (solid line) and temporal phase (dashed line). The inset shows the temporal profile over 4 cycles on a log scale. (d) Comparison of the measured unstreaked XUV spectrum (blue or dark gray dashed line) and the retrieved XUV spectrum (solid line) accompanied by the retrieved spectral phase (red or gray dashed line).