Dynamic property of the initial process in the dielectric relaxation phenomenon in KH₂PO₄

A new heterodyne experiment on the ferroelectric KH 2 PO 4 elucidates the extremely early stage of the excitation process of the ferroelectric relaxation mode. The time dependence of the response function G ( t ) shows a continuous rising from the time origin where the mode is excited by the ultra-short femtosecond pulses. The limit of the Debye model is overcome by a new phenomenological response function proposed here based on the experimental result.