Laser thermochemical technology for synthesizing optical diffraction elements utilizing chromium films

A technology was developed for synthesizing optical diffraction elements utilizing thin chromium films. It consists in directing a focused laser beam onto a substrate rotating at a constant angular velocity and coated with a thin chromium film, and subsequently processing it chemically in a selective etchant. Experiments were performed using a laser photoplotter to study the interaction of a continuously moving focused laser beam with chromium films deposited on glass substrates. The dependences were investigated of the widths of the tracks which were formed on the velocity of motion of the light spot and on the applied power. The new technology was used to show that diffraction structures having a resolution of better than 1000 mm^–1 could be recorded. The practical possibilities of the technology were illustrated by preparing masks for Fresnel zone plates having a numerical aperture of 0.65 and a diameter of 47 mm, at a wavelength of 0.63 μ. The energy distribution in the Airy disk of these plates was close to the diffraction limit.