We report on a recently developed laser-based diagnostic which allows direct
measurements of ray-deflection angles in one axis, whilst retaining imaging
capabilities in the other axis. This allows us to measure the spectrum of
angular deflections from a laser beam which passes though a turbulent
high-energy-density plasma. This spectrum contains information about the
density fluctuations within the plasma, which deflect the probing laser over a
range of angles. The principle of this diagnostic is described, along with our
specific experimental realisation. We create synthetic diagnostics using
ray-tracing to compare this new diagnostic with standard shadowgraphy and
schlieren imaging approaches, which demonstrates the enhanced sensitivity of
this new diagnostic over standard techniques. We present experimental data from
turbulence behind a reverse shock in a plasma and demonstrate that this
technique can measure angular deflections between 0.05 and 34 mrad,
corresponding to a dynamic range of over 500.