Modification of the photoelectron angular distribution through laser-induced continuum structure

We theoretically investigate how the photoelectron angular distribution is altered by the introduction of a dressing laser. The physical mechanism underlying this alteration is the so-called laser-induced continuum structure; namely, a strong dressing laser induces quantum mechanical interference, the degree of which is different for different ionization channels. Therefore the branching ratio into different ionization channels changes as a function of laser detuning, and accordingly the photoelectron angular distribution is altered. After a general argument, we present specific theoretical results for the K atom, which indeed exhibit significant modification of the photoelectron angular distribution.

Figure 1

Level scheme. $4p$ and $6p$ states of K atom are coupled by the linearly polarized probe and dressing lasers. With the laser intensities and the detuning range we have chosen for the present study, it is possible to consider each set of the fine-structure-resolved system, the K $4p_{1∕2}\text{−}6p_{1∕2}$ system and the K $4p_{3∕2}\text{−}6p_{3∕2}$ system. Incoherent ionization from state ∣1⟩ by the probe laser is also shown by the dashed line.

Figure 2

(a) Total and partial ionization yields into each $ϵs$ and $ϵd$ continuum, and (b) the branching ratio between them for the K $4p_{1∕2}\text{−}6p_{1∕2}$ system as a function of two-photon detuning $\delta$. Pulse durations and peak laser intensities are chosen to be ${\tau }_p=4\mathrm{ns}$ and $I_p=1\mathrm{MW}∕{\mathrm{cm}}^2$, and ${\tau }_d=4\mathrm{ns}$ and $I_d=100\mathrm{MW}∕{\mathrm{cm}}^2$, for the probe and dressing lasers, respectively.

Figure 3

Same as Fig. 2 only with the different pulse durations of ${\tau }_p=1\mathrm{ns}$ and ${\tau }_d=10\mathrm{ns}$ for the probe and dressing lasers, respectively.

Figure 4

Three-dimensional photoelectron angular distribution for the K $4p_{1∕2}\text{−}6p_{1∕2}$ system at three different two-photon detunings $\delta =-4$, 0.2, and $0.64\mathrm{GHz}$. Pulse durations and peak intensities are ${\tau }_p=1\mathrm{ns}$ and $I_p=1\mathrm{MW}∕{\mathrm{cm}}^2$ for the probe laser, and ${\tau }_d=10\mathrm{ns}$ and $I_p=100\mathrm{MW}∕{\mathrm{cm}}^2$ for the dressing laser.

Figure 5

Variations of the asymmetry parameters ${\beta }_0$ and ${\beta }_2$ for the K $4p_{1∕2}\text{−}6p_{1∕2}$ system as a function of two-photon detuning $\delta$ for the three different dressing laser intensities $I_d=100$, 200, and $500\mathrm{MW}∕{\mathrm{cm}}^2$. All other parameters are kept the same as those for Fig. 3, i.e., ${\tau }_p=1\mathrm{ns}$, ${\tau }_d=10\mathrm{ns}$, and $I_p=1\mathrm{MW}∕{\mathrm{cm}}^2$.

Figure 6

(a) Total and partial ionization yields into each $ϵs$ and $ϵd$ continuum, and (b) the branching ratio between them for the K $4p_{3∕2}\text{−}6p_{3∕2}$ system as a function of two-photon detuning $\delta$. Pulse durations and peak laser intensities are ${\tau }_p=1\mathrm{ns}$ and $I_p=1\mathrm{MW}∕{\mathrm{cm}}^2$, and ${\tau }_d=10\mathrm{ns}$ and $I_d=100\mathrm{MW}∕{\mathrm{cm}}^2$, for the probe and dressing lasers, respectively.

Figure 7

Three-dimensional photoelectron angular distribution for the K $4p_{3∕2}\text{−}6p_{3∕2}$ system at three different two-photon detunings $\delta =-4$, 0.12, and $0.6\mathrm{GHz}$. Pulse durations and peak intensities are ${\tau }_p=1\mathrm{ns}$ and $I_p=1\mathrm{MW}∕{\mathrm{cm}}^2$ for the probe laser, and ${\tau }_d=10\mathrm{ns}$ and $I_p=100\mathrm{MW}∕{\mathrm{cm}}^2$ for the dressing laser.

Figure 8

Variations of the asymmetry parameters ${\beta }_0$, ${\beta }_2$, and ${\beta }_4$ for the K $4p_{3∕2}\text{−}6p_{3∕2}$ system as a function of two-photon detuning $\delta$ for the three different dressing laser intensities $I_d=100$, 200, and $500\mathrm{MW}∕{\mathrm{cm}}^2$. All other parameters are kept the same as those for Fig. 6, i.e., ${\tau }_p=1\mathrm{ns}$, ${\tau }_d=10\mathrm{ns}$, and $I_p=1\mathrm{MW}∕{\mathrm{cm}}^2$.