Use of steel substrates in diffractive optics: Near field of high surface quality steel tape gratings

Abstract

a b s t r a c tSteel tape is used in optical applications due to its mechanical properties. However, roughness of steel surfaces affects to wave propagation. The effect can be observed using diffraction gratings with low periods. In such a case, self-images of the grating appear at certain periodic distances from the grating (Talbot planes). When standard steel is used, the contrast of Talbot self-images strongly decreases with the distance from the grating. In this work, we prove that controlling the surface quality of steel, it is possible to improve its optical behavior and, as a consequence, high quality surface steel represents a good choice for diffractive optics when the use of chrome-on-glass masks is not indicated. As an example, we have manufactured a diffraction grating over a high quality steel surface by means of an ablation process with a nanosecond pulsed laser. The contrast of the self-images for these gratings decreases very slowly with the distance, in comparison with the self-images obtained with standard steel tape gratings.

Diffraction gratings over cylindrical surfaces by laser ablation

“…Cuando estudiamos el comportamiento de las redes de difracción en el régimen de Fresnel (campo cercano, cuando el período de la rejilla es mucho mayor que la longitud de onda) aparece el efecto Talbot [7][8][9][10][11]. Este efecto consiste en la aparición de una serie de autoimágenes de la red, que son planos separados periódicamente una distancia conocida como distancia de Talbot:…”

Far field diffraction of gratings with two roughness levels

“…The approach carried out along this manuscript is valid as long as the correlation length of roughness and the period of the grating were longer than the illumination wavelength. As it was pointed out, steel tape gratings manufactured by laser ablation on a steel substrate can be assumed as a particular case of the grating proposed in this manuscript [15,16].…”

Diffraction by gratings with random fill factor

“…The most adequate method for fabrication depends on the substrate of the grating, the desired grating type, the needed accuracy, the desired feature, and so on. For example, gratings over glass substrates are usually fabricated by photo-lithographic methods [10] and gratings over steel substrates are commonly manufactured by laser ablation [11]. Despite manufacturing processes have been improved year after year, manufacturing errors are still present and become more notorius when period of the gratings approaches the wavelength of the incident light beam.…”