Vortex creation, annihilation, and nonlinear dynamics in atomic vapors

We exploit techniques for generating vortices and controlling their interactions in an optical beam in a nonlinear atomic vapor. A precise control of the vortex positions allows us to observe strong interactions leading to vortex dynamics involving annihilations. With this improved controlled nonlinear system, we get closer to the pure hydrodynamic regime than in previous experiments while a wavefront sensor offers us a direct access to the fluid's density and velocity. Finally, we developed a relative phase shift method which mimics a time evolution process without changing nonlinear parameters. These observations are an important step toward the experimental implementation of a two-dimensional turbulent state.

Figure 1

Experimental scheme: Successive images show how the system evolves from the engineered initial condition after propagating along the renormalized effective time $t\propto z/z_{\mathrm{NL}}$.

Figure 2

Experimental observation of vortex creation by increasing the relative angle in the $\mathit{xz}$ plane between beams (a) $\theta =0$, (b) $4.4\times {10}^{-4}$ rad, (c) $5.2\times {10}^{-4}$ rad, and (d) is a zoomed vortex pair with fluid density (colormap) and velocity (vectors, normalized by $c_s$ shown as the white arrow).

Figure 3

Experimental observation of creation and interaction of vortices. We are using an initial convergent elliptical beam which is shifted by a phase $\phi$ relative to the background beam (a)–(d) $\phi =0.96\pi ,1\pi ,1.05\pi ,1.10\pi$, respectively.

Figure 4

Numerical simulations of the converging configuration ($R=-0.5\mathrm{m}$). (a) and (b) Corresponding to a propagation along the time axis, respectively, $z/z_{\mathrm{NL}}=35$ and $z/z_{\mathrm{NL}}=70$ while (c) and (d) have the same effective time of propagation $z/z_{\mathrm{NL}}=50$ but relative phase is, respectively, $0.97\pi$ and $1.05\pi$.

Figure 5

Experiment (a) and (b) versus numerical simulation (c) and (d) of the diverging case $R=0.5\mathrm{m}$. Evolution is done by scanning the relative phase: (a) and (c) and (b) and (d) correspond, respectively, to $\phi =0.95\pi \text{and}1.08\pi$.

Figure 6

Transmission of the laser beam through the cell as a function of the detuning $\delta$ of the laser. From the transmission profile a fit to the data allows us to deduce the temperature of the gas. For this particular curve, we find $T={110}^{\circ }\mathrm{C}$.