A device for generating terahertz radiation using a phase matched optical rectification technique. The device converts laser radiation to terahertz radiation via a particular type of photonic downconversion. The device includes a crystalline material suitable for photonic downconversion of laser radiation, a first coupling component for coupling the laser radiation to the crystalline material and a second coupling component for coupling the generated terahertz radiation from the crystalline material to the environment. By sustaining the phase matching condition over a significant distance, the device is capable of providing terahertz radiation with high peak and average power. Also disclosed is a method for generating terahertz radiation including the steps of optically coupling laser radiation to a crystalline material suitable for downconversion of the laser radiation to terahertz radiation, downconverting the laser radiation to terahertz radiation and optically coupling the generated terahertz radiation from the crystalline material to the environment.