Abstract
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.
Highlights
Diffractive optical elements serve in many light systems today as dynamic or static devices, for example, Spatial Light Modulators [1] or Computer Generated Holograms (CGH) [2], to serve in pulse shaping, 3D imaging, microscopy, optical tweezers, and beam shaping [1, 3, 4]
The insight into the Talbot self-imaging oscillation first presented in Fig. 1 revealed a fundamental restriction on the available diffraction efficiency from high resolution, low refractive index contrast phase gratings
Femtosecond laser fabrication of multi-level phase gratings was applied inside bulk glass and found to verify the importance of layering on Talbot planes as well as demonstrate an 8-fold enhancement of the diffraction efficiency with the appropriate assembly of 8 grating layers
Summary
Diffractive optical elements serve in many light systems today as dynamic or static devices, for example, Spatial Light Modulators [1] or Computer Generated Holograms (CGH) [2], to serve in pulse shaping, 3D imaging, microscopy, optical tweezers, and beam shaping [1, 3, 4]. Modeling shows high diffraction efficiency is available for an optimized number of ideally separated grating layers We exploit these concepts in the context of femtosecond laser writing of weakly diffracting and finely pitched phase gratings inside fused silica glass, and definitively demonstrate for the first time the coherent and incoherent collective response of multilayer stacked gratings that respectively enhance or diminish the diffraction efficiency according to their stacking period and number of grating layers. With this new understanding, a realm of new opportunities is available for the harnessing of weakly diffracting DOEs for high resolution applications
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