The use of diffractive optical elements ( DOE ) in most refractive reimaging infrared optical systems significantly simplifies the optical design form and improves the image quality. The basic theory of chromatic aberration correction using DOE is analyzed. A 3 to 5 um design is shown comparing the optical design form and image quality of the conventional design and the DOE improved design. The DOE improves performance while lowering cost and weight by reducing the number of lens elements and desensitizing the design to misalignments. MTF, MRT, and NEDT tests of the hardware empirically demonstrate the superior performance of the DOE design.