Monochromatic THz emission by optically excited lattice vibrations in KRe(MoO4)2

Abstract

Coherent infrared-active optical phonons in KY(MoO4)2 are excited by a broadband THz pulse and re-emit monochromatic THz radiation with the dipole decay time of 33 ps. Such slow decay is an exception for the oscillators in solids with frequencies below 1 THz. By studying dependencies of the THz-TDS spectra on the sample temperature and thickness, we show that the beating observed in Fig.1c is due to a strong absorption for the radiation polarized along the c axis (Eω ║ c). Long lifetime of the coherent emission allows for the detection of more than 50 periods of radiation with frequency of 568 GHz for Eω ║ a. Thus, the remarkably long decay time of the optical phonons in KRe(MoO4)2 together with the chemical stability of these compounds suggest a variety of possible applications of such class of dielectrics in THz technology.