We designed experimental equipment realizing one of the time-spectroscopy methods for detail investigation of photorefractive process in the DKDP single crystal at room temperature. A non-steady-state optic-polarization technique with a pulse pumping (pulse duration of Q- switched YAP:Nd3+-laser was approximately 20 ns, energy density of pulses varied from 0.2 J/cm2 up to 1.6 J/cm2) has been used in experiments. This allowed us to achieve temporal resolution for responses of various components of photorefractive (PR) effect with different characteristic times (acoustic component is approximately 12 ms, fast component is approximately 1 ms and slow component is from 4 ms up to 100 ms). As a result a linear dependence of the pumping-induced internal field magnitude on pumping pulse energy at the 1.08 mm is established. It was shown for the first time that mechanisms of excitation of fast and slow components are independent. The present results may create basis for detail PR effect investigations of the KDP group crystals above the Curie point with prospect of further holographic applications and a new technique to measure laser pulses energy.