Silicon Diffractive Optical Element with Piecewise Continuous Profile to Focus High-Power Terahertz Radiation into a Square Area

A technique of high-frequency laser ablation using a 2D beam scanner has been designed and applied to creation of a silicon diffractive optical element (DOE) with a continuous profile to focus a terahertz Gaussian beam into a square region. The microrelief of the resulting silicon DOE has been analyzed with a white-light interferometer and a scanning electron microscope. The distribution of radiation behind the DOE illuminated by a high-power beam of the Novosibirsk free-electron laser at a wavelength of 130 µm, recorded with a pyroelectric camera, has been demonstrated. The measured diffraction efficiency of the DOE is equal to 97 ± 2 % .