We investigate the possibility of constraining the dark energy equation of state by measuring the ratio of Einstein radii in a strong gravitational lens system with two source planes .
This quantity is independent of the Hubble parameter and directly measures the growth of angular diameter distances as a function of redshift .
We investigate the prospects for a single double source plane system and for a forecast population of systems discovered by re-observing a population of single source lenses already known from a photometrically selected catalogue such as CASSOWARY or from a spectroscopically selected catalogue such as SLACS .
We find that constraints comparable to current data-sets ( \sigma ( w ) \sim 15 \% ) are possible with a handful of double source plane systems .
We also find that the method ’ s degeneracy between \Omega _ { \text { M } } and w is almost orthogonal to that of CMB and BAO measurements , making this method highly complimentary to current probes .