Enhanced terahertz fingerprint detection with ultrahigh sensitivity using the cavity defect modes.

We report a new scheme of realizing terahertz fingerprint detection with ultrahigh sensitivity. Instead of using the direct absorption of terahertz through a bare sample in the regular transmission scheme, a cavity mode resonating at the characteristic frequency of the sample is used and due to the high dependence of the cavity mode transmission on the material loss, an amplified transmission decaying is observed when the sample is loaded into the cavity. Furthermore, this scheme retains the feature of substance identification. A one-dimensional photonic crystal cavity is used as the example for the detection of α-lactose and an efficient detection of 10 nm α-lactose can be achieved, which corresponds to 1/57000 of the free space wavelength at the characteristic frequency of 0.529 THz, exhibiting a sensitivity over 400 times higher than the regular transmission method.