Terahertz (THz) radiation has been observed from multiferroic ${\mathrm{BiFeO}}_3$ thin films via ultrafast modulation of spontaneous polarization upon carrier excitation with illumination of femtosecond laser pulses. The radiated THz pulses from ${\mathrm{BiFeO}}_3$ thin films were clarified to directly reflect the spontaneous polarization state, giving rise to a memory effect in a unique style and enabling THz radiation even at zero-bias electric field. On the basis of our findings, we demonstrate potential approaches to ferroelectric nonvolatile random access memory with nondestructive readability and ferroelectric domain imaging microscopy using THz radiation as a sensitive probe.

• Received 7 September 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.117402