Effects of laser polarization on photoelectron angular distribution through laser-induced continuum structure

We theoretically investigate the effects of laser polarization on the photoelectron angular distribution through laser-induced continuum structure. We focus on a polarization geometry where the probe and dressing lasers are both linearly polarized and change the relative polarization angle between them. We find that the total ionization yield and the branching ratio into different ionization channels change as a function of the relative polarization angle, and accordingly the photoelectron angular distribution is altered. We present specific results for the $4p_{1∕2}\text{−}6p_{1∕2}$ and $4p_{3∕2}\text{−}6p_{3∕2}$ systems of the K atom and show that the change of the polarization angle leads to a significant modification of the photoelectron angular distribution.

Figure 1

Quantization axis and the polarization vectors ${\mathbf{e}}^{\left(p\right)}$ and ${\mathbf{e}}^{\left(d\right)}$ for the probe and dressing lasers defined for this work. The polarization vector ${\mathbf{e}}^{\left(p\right)}$ lies in the $x\text{−}z$ plane, and the quantization axis is taken along the $z$ axis.

Figure 2

(Color online) Level scheme considered in this paper for the K $4p_{1∕2}\text{−}6p_{1∕2}$ system. Depending on the polarization angle of the probe laser, ${\theta }_p$, different transition paths have to be considered. (a) ${\theta }_p=0°$, (b) ${\theta }_p=90°$, and (c) $0°<{\theta }_p<90°$. A similar level scheme can be drawn for the K $4p_{3∕2}\text{−}6p_{3∕2}$ system.

Figure 3

(Color online) (a) Total ionization yield and (b) the branching ratio between the partial ionization yields into each $ϵs$ and $ϵd$ continuum 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 ${\tau }_p=1\mathrm{ns}$ 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. The polarization angle takes the values of ${\theta }_p=0°$, 30°, 60°, and 90°.

Figure 4

(Color online) (a) Total ionization yield and (b) the branching ratio between the partial ionization yields into each $ϵs$ and $ϵd$ continuum 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 $500\mathrm{MW}∕{\mathrm{cm}}^2$. The intensity of the probe laser is $I_d=1\mathrm{MW}∕{\mathrm{cm}}^2$. Pulse durations are chosen to be ${\tau }_p=1\mathrm{ns}$ and ${\tau }_d=15\mathrm{ns}$ for the probe and dressing lasers, respectively. The polarization angle is ${\theta }_p=30°$.

Figure 5

Three-dimensional photoelectron angular distribution due to one-photon ionization from the K $4p_{1∕2}$ state by the probe laser field only at three different polarization angles ${\theta }_p=0°$, 45°, and 90°. Pulse duration and peak intensity are ${\tau }_p=1\mathrm{ns}$ and $I_p=1\mathrm{MW}∕{\mathrm{cm}}^2$ for the probe laser. The view point is from the positive $y$ axis.

Figure 6

Three-dimensional photoelectron angular distribution for the K $4p_{1∕2}\text{−}6p_{1∕2}$ system at three different two-photon detunings $\delta =-4$, $-0.62$, and $0.44\mathrm{GHz}$. 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. The polarization angle is ${\theta }_p=60°$.

Figure 7

(Color online) (a) Total ionization yield and (b) the branching ratio between the partial ionization yields into each $ϵs$ and $ϵd$ continuum 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 chosen to be ${\tau }_p=1\mathrm{ns}$ 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. The polarization angle takes the values ${\theta }_p=0°$, 30°, 60°, and 90°.

Figure 8

(Color online) Same as in Fig. 4 but for the K $4p_{3∕2}\text{−}6p_{3∕2}$ system.

Figure 9

Same as in Fig. 5 but for the K $4p_{3∕2}\text{−}6p_{3∕2}$ system. The viewpoint is from the positive $y$ axis.

Figure 10

Three-dimensional photoelectron angular distribution for the K $4p_{3∕2}\text{−}6p_{3∕2}$ system at three different two-photon detunings $\delta =-4$, $-0.89$, and $0.42\mathrm{GHz}$. 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. The polarization angle is ${\theta }_p=60°$.

Figure 11

Linear dichroism for the (a) K $4p_{1∕2}\text{−}6p_{1∕2}$ system and (b) K $4p_{3∕2}\text{−}6p_{3∕2}$ system as a function of two-photon detuning $\delta$. 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.