Do you know where I could find more info about this ? because it sounds interesting...Isn't that how a 3D holograph is "recorded" based on the 3D target that it is trying to recreate? With beam splitting, you may be able to accurately measure distance by refocusing the blurred reflection pattern generated by the dual-beam interaction. The focal parameter would then be a function of the distance. Time and material type should then become irrelevant because the beams are referencing each other, both traveling the same distance and through the same material thus cancelling out any density fluctuations or movement of the target.