Polarization Control in Three-Dimensional Resonant Coherent Excitation

We present an experimental demonstration of an ingenious technique to control the alignment of the atomic internal state in the x-ray region using a periodic crystal field. The alignment directions of ${\mathrm{Ar}}^{16+}$ and ${\mathrm{Fe}}^{24+}$ ions were readily controlled by selecting the array of atomic planes using three-dimensional resonant coherent excitation, and were probed via the anisotropy of the deexcitation x-ray emission. We applied this method to a double resonance experiment, and succeeded in controlling the population of the specific magnetic substate in a $\Lambda$-type three-level configuration.

Figure 1

(a) Orthogonal coordinate system of a Si crystal. $\theta$ and $\varphi$ are the ion incident angles with respect to the $[\overline{1}10]$ axis. (b) Schematic layout of the experimental setup. Two Si(Li) x-ray detectors were installed in the horizontal and vertical planes. The target crystal was mounted on a high-precision three-axis goniometer.

Figure 2

(a) The $K\alpha$ x-ray yields from $416\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Ar}}^{16+}$ in the horizontal (○) and vertical (●) directions, excited by the ${\mathbf{g}}_{1,-1,0}$, ${\mathbf{g}}_{1,-1,-2}$, and ${\mathbf{g}}_{1,-1,-4}$ components, respectively. Corresponding arrays of atomic planes are shown in the insets. The transition energy was scanned by tilting $\theta$ at $\varphi =-0.23°$. (b) The $K\alpha$ x-ray yields from $423\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Fe}}^{24+}$ excited by the ${\mathbf{g}}_{2,-1,-1}$, ${\mathbf{g}}_{2,-1,-3}$, and ${\mathbf{g}}_{2,-1,-5}$ components, respectively, at $\varphi =-0.11°$. The solid lines are the fitted curves. The angles $\varphi$ were selected to be enough larger than the critical angle for planar channeling (0.0095°).

Figure 3

(a) The squared amplitude of the oscillating field in the ion rest frame. (b) The experimental and calculated values of the $V/H$ ratio.

Figure 4

(a) The $\Lambda$-type three-level configuration of ${\mathrm{Ar}}^{16+}$. (b) The uncoupled (left-hand side) and the coupled (right-hand side) scheme of the probed state. (c) The $K\alpha$ x-ray yields from $416\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Ar}}^{16+}$ in the horizontal (○) and vertical (●) directions, excited by the ${\mathbf{g}}_{1,-1,0}$, ${\mathbf{g}}_{1,-1,-2}$, and ${\mathbf{g}}_{1,-1,-4}$ components, respectively, under the double resonance condition ($\varphi =-0.128°$). The arrows indicate the polarization directions of the probing field relative to the coupling field.