  We describe a procedure by which a long ($\gtrsim 1\,\mathrm{km}$) optical
path through atmospheric turbulence can be experimentally simulated in a
controlled fashion and scaled down to distances easily accessible in a
laboratory setting. This procedure is then used to simulate a 1-km-long
free-space communication link in which information is encoded in orbital
angular momentum (OAM) spatial modes. We also demonstrate that standard
adaptive optics methods can be used to mitigate many of the effects of thick
atmospheric turbulence.
