  Terahertz time domain spectroscopy has been used to study low frequency
confined acoustic phonons of silver nanoparticles embedded in poly(vinyl
alcohol) matrix in the spectral range of 0.1 to 2.5 THz. The real and imaginary
parts of the dielectric function show two bands at 0.60 THz and 2.12 THz
attributed to the spheroidal and toroidal modes of silver nanoparticles, thus
demonstrating the usefulness of terahertz time domain spectroscopy as a
complementary technique to Raman spectroscopy in characterizing the
nanoparticles.
