Transmissive quasi-optical Ronchi phase grating for terahertz frequencies.

A transmissive, square-wave Ronchi phase grating has been fabricated from the dielectric polytetrafluoroethylene to diffract an ~0.7 THz beam quasi-optically. When illuminated by a coherent, cw terahertz (THz) source, the spot separation of the ±1 diffractive orders and the diffraction efficiency were measured as a function of THz frequency and rotation angle. The grating performance depends sensitively on the refractive index, whose value can be measured with an accuracy limited by the fabrication precision. The use of these gratings for polarization-insensitive quasi-optical imaging and phased arrays is discussed.