Femtosecond laser direct writing of a Fresnel zone plate in glasses for mid-infrared imaging applications

Pierre Delullier; Guillaume Druart; Florence de la Barrière; Laurent Calvez; Matthieu Lancry

doi:10.1117/12.2600695

28 October 2021 Femtosecond laser direct writing of a Fresnel zone plate in glasses for mid-infrared imaging applications

Pierre Delullier, Guillaume Druart, Florence de la Barrière, Laurent Calvez, Matthieu Lancry

Author Affiliations +

Proceedings Volume 11889, Optifab 2021; 1188912 (2021) https://doi.org/10.1117/12.2600695
Event: SPIE Optifab, 2021, Rochester, New York, United States

Abstract

An important challenge in infrared imaging today consists in addressing the SWaP problem (Size, Weight and Power), for example by simplifying as much as possible the optical system before the sensor. The work presented in this paper takes advantage of recent techniques in femtosecond laser direct writing to imprint optical systems. This work aims at merging a lens array with a filter array by writing gradient index lenses with a femtosecond laser inside a dedicated glass substrate. A classical gradient index lens requires a huge refractive index variation, which cannot be reached today with femtosecond laser processing (Δ𝑛_𝑚𝑎𝑥 ~ 0,05). So, we decided to turn towards writing a gradient index Fresnel lens. A first-order Fresnel lens was designed with a Δ𝑛_𝑚𝑎𝑥 < 5.10⁻²discretised into 8 index levels to guarantee a diffraction efficiency of 85% on the overall spectral bandwidth of the filters. We studied a chalcogenide glass because of his good properties in mid-IR optics. We compared the different laser responses of the material: threshold of permanent changes, quantitative phase and index variation. Finally, we showed that reaching a phase variation of π radians with femtosecond laser writing is possible even for a huge scanning speed (0,01 mm/s up to 25 mm/s). By overlapping the written lines, we were able to implement a maximum phase variation of 8 radians (with only one written layer), demonstrating the possibility to write quickly a GRIN Fresnel lens with a diameter of some millimeters.

Conference Presentation

Citation Download Citation

Pierre Delullier, Guillaume Druart, Florence de la Barrière, Laurent Calvez, and Matthieu Lancry "Femtosecond laser direct writing of a Fresnel zone plate in glasses for mid-infrared imaging applications", Proc. SPIE 11889, Optifab 2021, 1188912 (28 October 2021); https://doi.org/10.1117/12.2600695

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