Coherent stitching of light in multilayered diffractive optical elements.

Diffractive optical elements serve an important function in many dynamic and static optical systems. Multilayered diffractive elements offer powerful opportunity to harness both phase and amplitude modulation for benefits in diffraction efficiency and beam shaping. However, multilayered combinations have been difficult to fabricate and provide only weak diffraction for phase gratings with low refractive index contrast. Femtosecond laser writing of finely-pitched multilayer volume gratings was optimized in bulk fused silica. We identify and quantify an optimum layer-to-layer separation according to Talbot self-imaging planes and present systematic experimental validation of this new approach to enhance otherwise weakly diffracting volume gratings.