Device for protecting an optical system against excess luminosity

A device for protecting an optical system against excess luminosity of an incident light beam, said device comprising:

• means for forming first and second light beams from said incident light beam;
• an optical reflection means;
• first optical means for guiding said first light beam toward said optical system after reflection on said reflection means;
• and
• second optical means for guiding said second light beam toward said reflection means along a second optical path, the first optical path followed by said first light beam to said reflection means being longer than said second optical path,
• wherein said optical reflection means is a mirror comprising a reflecting layer capable of being ablated at least locally when it is subjected to a luminous intensity higher than a predefined value, and in that said first and second optical means respectively focus said first and second light beams on a same focusing point of said reflecting layer of said mirror and form first and second paths having a length difference such that, when said incident light beam has excess luminosity, said second light beam initiates ablation of said reflecting layer at said focusing point, said ablation being continued and completed by combined action of said first and second light beams.