Recently, there was a publication regarding some new materials that would let thru light in one direction and either absorb it or reflect it in the other direction; the publication does not clarify on which one. It does not get as well into other important details as the bandwidth where the diode is effective.
This is interesting because if this really does what they say it does, it is potentially a way to drive a spaceship without any propellant or propulsion energy expenditure.
Assuming the effective bandwidth is not in some dark region of the cosmic spectra, you could conceive a radiation sail with this material, and reach significant speeds over a few years of acceleration. But for doing any concrete estimations, we need hard numbers on the transmittivity and dielectric eigenvalues of these things or something that would allow to calculate the expected impulse. Do anyone knows how to find more info on this material? that MIT article does provide a reference to the paper, but i don't have access to that journal gateway, and the abstract is really scant on the interesting details (probably because they are orienting its application for optical computing!)