Towards laser-based manufacturing of freeform fused silica image slicers

Abstract

Integral field spectroscopy (IFS) enables the simultaneous acquisition of spatial and spectral information across a two-dimensional field of view, making it a powerful technique for modern astronomical instrumentation. Among the various integral field unit (IFU) architectures, image slicers are an elegant solution with high spatial efficiency and intrinsically achromatic operation. Despite their numerous optical advantages and successful use in both ground- and space-based observatories, the fabrication of image slicers remains challenging due to the stringent surface quality, figure accuracy, and alignment tolerances required, thereby limiting their wider adoption. In this work, we demonstrate the potential of ultrafast laser-assisted etching (ULAE) as a versatile manufacturing approach for fused-silica image slicers. A prototype consisting of twenty individual slices was fabricated with integrated passive alignment features. Optical profilometry was used to assess the geometric accuracy of both the individual components and the assembled system. To achieve the surface quality required for astronomical applications, carbon dioxide (CO2) laser polishing was investigated as a post-processing technique. Preliminary polishing experiments indicate that sub-5 nm surfaces roughness can be obtained, demonstrating the compatibility of CO2 laser polishing with ULAE-fabricated fused silica optics. These results establish a promising route towards the rapid and scalable fabrication of image slicers and other complex freeform optical components for future astronomical instruments.