Strong Field Quantum Path Control Using Attosecond Pulse Trains

We show that attosecond pulse trains have a natural application in the control of strong field processes. In combination with an intense infrared laser field, the pulse train can be used to microscopically select a single quantum path contribution to a process that would otherwise consist of several interfering components. We present calculations that demonstrate this by manipulating the time-frequency properties of high order harmonics at the single atom level. This quantum path selection can also be used to define a high resolution attosecond clock.

Figure 1

Harmonic spectra generated by a $4\times {10}^{14}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ IR pulse alone (blue lines), or in combination with a ${10}^{13}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ attosecond pulse train (red lines), for five different values of the delay between the two pulses. The delays are, in units of the IR cycle, (a) $t_d=-0.25$, (b) $t_d=-0.16$, (c) $t_d=-0.094$, (d) $t_d=-0.063$, and (e) $t_d=+0.063$.

Figure 2

(a) Chirp rates vs harmonic order for three different peak intensities of the IR pulse; $I_1=3\times {10}^{14}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ (open squares), $I_1=4\times {10}^{14}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ (solid squares), and $I_1=5\times {10}^{14}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ (open circles). (b) Comparison of chirp rates of the full calculation (symbols) at the two good delays (see text) to those of the simple model (lines), for an IR intensity of $I_1=4\times {10}^{14}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$. We show both the downhill (solid squares/solid line) and the uphill (open circles/dashed line) results.

Figure 3

Return energy as a function of the release time. Left hand curve: uphill trajectories; right hand curve: downhill trajectories. The IR intensity is $4\times {10}^{14}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$. On each curve the long quantum path (${\alpha }_2$) is shown as a dotted line and the short quantum orbit (${\alpha }_1$) is shown as a solid line. The five labels (a)–(e) correspond to the panels in Fig. 1.