We have experimentally studied for the first time a new operation principle of the coherent diffractional pulse shaper (Rabi shaper). In the experiment, we observed an effect of tunable pulse shaping of nanosecond semiconductor laser pulse during the resonant pumping of the D₂ line (780.24 nm) of ⁸⁷Rb vapor in the range of self-diffraction angles φ = ± 4^о. We observed the synthesis of nanosecond 0π-pulses at the small length of the nonlinear interaction 0.1...1 mm. We propose to use the Rabi shaper as an energy efficient tunable shaper of classical and single-photon wave packets. We analyze a possibility of the Rabi shaper operation in quantum systems with feedback.