Diffractive optical element comprising a metasurface for TIRF microscopy

A diffractive optical element comprising:

• a substrate having a first surface and a second surface opposite the first surface, which substrate is transparent to light in at least one spectral range and has, in said spectral range, a refractive index higher than that of water;
• at least one metasurface made of a dielectric material and placed on said first surface of the substrate, the metasurface being formed through a repetition of a pattern that is periodic in two directions, x and y, that are perpendicular to each other and parallel to a surface of the substrate, said pattern comprising a sub-pattern comprising a first strip segment that is rectilinear along y,
• the metasurface comprising a first strip of dashes in the direction y, said strip of dashes being formed from said sub-pattern,
• said periodic pattern further comprising a second strip segment that is rectilinear in the direction y, so that the metasurface comprises a second strip that is continuous in a direction y,
• said metasurface being suitable for diffracting light radiation of wavelength λ comprised in said spectral range, and incident with an angle of incidence, to form diffracted radiation, said diffracted radiation being formed in such a way that it propagates through the substrate, and strikes said second surface of the substrate at a diffracted angle θd larger than or equal to a limit angle θc of total internal reflection between said substrate and water,
• said metasurface being configured to have, at said angle of incidence, a transmittance lower than 5% for the order of diffraction 0 and a transmittance higher than 50% for diffracted radiation corresponding to an order of diffraction −1 or +1.