Optical reflective diffraction device having a high resistance to laser flux
The present invention relates to an optical device for reflective diffraction with high diffraction efficiency and high laser flux resistance. The device includes a protective structure having at least one mixture layer produced by a uniform mixture of a first material and of a second material, where both of these are dielectric, and wherein said first material has an optical index lower than that of the said second material.
1. An optical device for reflective diffraction of an incident light beam, comprising:
a reflecting structure having a stack of thin dielectric layers made alternately of a first dielectric material and of a second dielectric material, the first dielectric material having an optical index lower than that of the second dielectric material,
a protective structure deposited on a thin dielectric layer made of the first dielectric material of the stack of the reflecting structure, the protective structure including at least a first mixture layer formed of a homogenous mixture of the first and second dielectric materials, the optical index of the first mixture layer being higher than that of the first dielectric material;
wherein the protective structure comprises exclusively said first mixture layer; and
wherein a periodic arrangement of patterns is etched on a free surface of the said protective structure, in said mixture layer, so as to form a diffraction grating.
2. An optical device for reflective diffraction of an incident light beam according to claim 1 wherein said first dielectric material is SiO 2 .
3. An optical device for reflective diffraction of an incident light beam according to claim 2 wherein said second dielectric material is HfO 2 .
4. An optical device for reflective diffraction of an incident light beam according to claim 3 wherein said first mixture layer contains at least 5% of SiO 2 .
5. An optical device for reflective diffraction of an incident light beam according to claim 4 including a substrate on which the reflecting structure is disposed.
6. An optical device for reflective diffraction of an incident light beam according to claim 5 wherein said substrate is metallic.
7. An optical device for reflective diffraction of an incident light beam according to claim 5 , including a layer of a metallic material, positioned between the said reflecting structure and the said substrate.