Ultrafast response of negative index metamaterials in the near-infrared

Nanoimprint lithography is used to fabricate a metamaterial with the "fishnet" structure composed of Ag/a-Si/Ag layers that exhibits negative refractive index in the near-infrared. We have carried out a femtosecond pump-probe experiment to measure the transient photo-induced response of this structure. With a pump fluence of 330μJ/cm 2 at 800nm, the transmission at the magnetic resonance is increased by ~15.4%. The induced change originated from carrier excitation in the a-Si layer has a fast decay constant of 1.1ps.