Shape Retrieval of\nAzopolymer Surface Relief Gratings\nfrom Diffraction Efficiency Measurement

Azopolymers have enormous potential as real-time materials\nfor\nlithography. Light-induced surface deformations in these polymers\nenable single-step surface patterning, offering the possibility of\nfabricating reconfigurable diffractive optical components like gratings.\nWhile real-time measurement of the surface geometry is inherently\npossible, previous methods have relied on complex instruments. Conversely,\nsimple approaches based on real-time diffraction efficiency measurements\nof a probing light beam have provided only qualitative estimates of\nthe inscription process. Here, we propose a diffraction-based method\nfor the accurate real-time reconstruction of surface relief gratings\ninscribed on azopolymer films. Our method relies on the acquisition\nof the diffraction pattern of a probe beam during the SRG formation,\nand we allowed for surface geometry reconstruction through Fourier\ndecomposition with residual error below 3% and 50 ms temporal resolution.\nOur all-optical approach, directly integrable in any experimental\nconfiguration, provides direct access to the SRG inscription process,\nenabling real-time feedback for on-demand dynamic surfaces.