Terahertz micro-spectroscopy using a transient mirror technique

Terahertz (THz) spectroscopy of a biomolecule with spatial resolution below the diffraction limit of the radiation has been achieved by use of an all-optical, contactless transient mirror technique. A resolution of around 50 pm is determined by the use of a test sample of gold strip lines deposited on GaAs, and the differential THz time-domain spectroscopy (THz-TDS) response of biotin has been measured in both the presence and absence of the transient mirror at room temperature. These preliminary results demonstrate the potential for use of the technique for the chemical identification and characterisation of biomolecules in small volumes with the ultimate goal being microscopic imaging of live cells. The technique may find applications in quality control for semiconductor processing, and in identifying material imperfections, i.e. small cracks in non-destructive testing. We discuss the limitations of the transient mirror technique along with several advantages over other related techniques.