THZ ELECTROMAGNETIC EMISSION BY COHERENT INFRARED-ACTIVE PHONONS

Coherent phonons are excited in single-crystal tellurium by above-band -gap excitation with femtosecond laser pulses. Coherent infrared-activ e lattice vibrations give rise to the emission of electromagnetic wave s at the phonon frequency. The excitation mechanism is based on the ul trafast buildup of a photo-Dember field and the coupling of a polar la ttice mode to this field. The dynamics of the Dember field is obtained from a numerical simulation of the electron-hole plasma dynamics clos e to the crystals surface. This effect itself gives rise to a broadban d emission of THz radiation from highly absorbing semiconductor surfac es. Details of the generation and the outcoupling of the radiation are discussed.