Volumetric thermochemical laser writing of nanostructured reflective diffraction gratings on a dual-layer Zr/SiO₂ material

Subject of study. Volumetric thermochemical laser writing of nanostructured reflective diffraction gratings in a dual-layer Zr/SiO2 material is studied. Objective. Direct laser writing on thin zirconium films on fused silica substrates is comprehensively studied to determine the cause of the anomalously large phase shift and investigate the possibility of creating reflective diffraction structures on its basis with a potential application in the compo-nent base of photonics. Method. Thermochemical writing with a focused laser beam on zirconium films deposited on fused silica substrates makes it possible to form oxide micropatterns. Depth measurements of their relief on an atomic force microscope show a surface reliefno more than 10 nm deep. In contrast, measurement on a white light interferometer shows a relief up to hundreds of nanometers deep. Scanning electron microscopy and Raman spectra analysis provide information on the modified regions' internal structure and chemical composition. Main results. The effect of laser writing of nanostructured reflective diffraction gratings on a dual-layer material is three-dimensional because the layer is modified in depth by 50%-60% more than the initial thickness of the Zr film. In addition, gratings with a period equal to the laser beam scanning step are formed on the surface and in the depth of the modified layer. Depending on the power of the writing beam, the modified layer comprises a compo-sition of oxide and zirconium nitride in the amorphous or crystalline phases, including silicon oxide in the lower layer. The inner grating comprises channels in the modified layer, with a cross-section of approximately 80 nm. A hypothesis about the morphology and mechanism of the formation of nanogratings has been proposed. Practical significance. Supplementing the "dry" one-stage technology for manufacturing binary reflective diffraction struc-tures on a dual-layer Zr/SiO2 material with a stage of reactive ion etching for diffraction efficiency adjustment is achieved. (c) 2023 Optica Publishing Group