Figure 1

(a) DTLS of the cesium ${\mathrm{D}}_{\mathrm{2}}$ line used to investigate the nearly degenerate FWM process. The arrows represent the photons absorbed and emitted in this parametric process. (b) FWM spectrum observed for orthogonal polarization between the pumps and the signal beam. (c) Experimental setup: OI: optical isolator; BS: beam splitters; M: mirrors, L: lenses; AOMs: acousto-optic modulators. Inset: (1) voltage signal used to switch off the MOT beams and quadrupole magnetic field and to trigger the scanning voltage ramp (2). The injection beam with frequency $\omega -\delta$ is also intensity modulated according to this timing sequence.Reuse & Permissions

Figure 2

Observed light spatial distribution and interference pattern for the single charge ($m=1$, $p=0$) signal beam S: (a) and (c); and for the generated phase conjugate beam C: (b) and (d). The interferograms are obtained using, respectively, the reflected incident reference wave by mirror $M4$, and the corresponding generated reference wave [whose profile is shown in (e)] via the same FWM process. The presented images are obtained by subtracting from the corresponding image the dark image, recorded when the injection of the diode laser is blocked, where no coherent signal is observed.Reuse & Permissions

Figure 3

Same sequence of images as in Fig. 2, but for an incident signal beam S with a double topological charge ($m=2$, $p=0$).Reuse & Permissions