Real-time atmospheric compensation by stimulated Brillouin-scattering phase conjugation

We report the first demonstration to our knowledge of atmospheric compensation at extended ranges by stimulated Brillouin-scattering phase conjugation. With a field-of-view aperture product of 175 mm mrad, we studied horizontal ranges up to 6 km at a 2.5-m height above ground, with the refractive-index structure parameter Cn2 as large as 10−13 m−2/3. Compensation was achieved at all ranges, consistent with the turbulence-resolution capability of the 10-cm system aperture. The system was driven by frequency-doubled Nd:YAG lasers operating with ~10-ns pulses that were Raman shifted in gaseous hydrogen to the 683-nm operating wavelength. Raman amplification overcame as much as 85 dB of range and internal losses.