Terahertz diffractive optic elements have been fabricated in polypropylene by imprinting with a silicon master. A silicon master is created with eight phase levels for high diffraction efficiency and etched using inductively coupled plasma reactive ion etching. This technique enables the rapid replication of complex optical structures in a high transmission material. Excellent replication of multilevel high efficiency Fresnel lenses is shown. The resulting lenses were tested with a 2 THz quantum cascade laser. The signal strength at the focus was 70 times the base signal strength.