Fabrication of High-effective Silicon Diffractive Optics for the Terahertz Range by Femtosecond Laser Ablation

Comparison of the two laser sources (UV nanosecond and IR femtosecond) used for the formation of micro-relief at the silicon surface showed the advantage of the second one. A four-level silicon diffractive THz Fresnel lens has been fabricated by laser ablation at high repetition rate (f = 200 kHz) of femtosecond Yb:YAG laser. Features of the lens were investigated in the beam of the Novosibirsk free electron laser at the wavelength of 141 μm. Detailed results of investigation of fabricated lens micro-relief are presented. The measured diffractive efficiency of the lens is in good agreement with the theoretical prediction.