Diffractive Lenses for High Power Terahertz Radiation Beams

Techniques for manufacturing silicon binary (two level) diffractive lenses and polypropylene kinoform diffractive lenses for the terahertz spectrum range are described. The elements are 1 and 0.8 mm thick, respectively. The silicon lens is manufactured in two versions: with no coating and with a parylene C (polyparaxylylene) antireflection coating. Characteristics of the diffractive optical elements are studied in the beam of a pulse–periodic free electron laser at a radiation wavelength of 141 μm and a repetition rate of 5.6 MHz. The radiation resistance of the parylene coating, tested on the Novosibirsk free electron laser, was not impaired when the coating was exposed to an average power density of 4 kW cm–2, the peak power in a 100 picosecond pulse being almost 8 MW cm–2. DOI: 10.3103/S1062873813090037