Observation of Phase Conjugation of Light Arising from Enhanced Backscattering in a Random Medium

We measure the fundamental phase conjugation of a light field arising from enhanced backscattering in a multiple scattering medium. The measurements employ a two-window, time-resolved heterodyne method to suppress specularly reflected light and to determine the transverse Wigner function of the field, yielding joint amplitude and phase information. Using this method, a light field backscattered from an aqueous suspension of polystyrene spheres is found to reverse curvature relative to that of the incident field.

Figure 1

Experimental setup for our time-resolved two-window technique.

Figure 2

Measured Wigner functions $W(x,p)$. The vertical axis denotes the transverse angle $\theta$ in mrad, i.e., the transverse momentum, $p=\theta k$. The horizontal axis is the transverse position $x$ in mm. (a) Wigner function for the divergent field incident onto our random medium. The measured Wigner function for the enhanced-backscattered field (b) and the theoretical model (c) show a convergent field emerging from the sample. On the other hand, an incident convergent field (d) leads to a divergent enhanced-backscattered field; (e) shows the measured data, (f) the theoretical model.