Reflective diffraction grating operating around 3,3 THz for space applications

There is actual demand from astronomers for space instrumentation operating in the range of a few terahertz (between 1 and 10 THz) for deep space explorations. Analyzing this radiation coming from space is possible thanks to the development of a customized spectrometer, which splits the light collected at the terahertz spectral range using a diffraction grating. This diffraction grating has to be capable of withstanding the demanding conditions of space. However, obtaining the required dimensions, morphology, and wide spectral range for the grating is challenging. This work presents the outcomes of the diffraction efficiency verification for a metallic grating provided with a sawtooth profile and manufactured by laser micro-structuring with a 5-axis femtosecond laser system on an aluminum, fulfilling those requirements. The grating operates only with the first diffraction order (m=-1), favoring the transverse magnetic (TM) polarization over the transverse electric (TE) component, with a view to its incorporation in a polarization-selective optical system. In the course of the work, the grating characteristics, fabrication methods, and experimental verification of the grating properties, morphology, and diffraction efficiency will be presented. Diffraction efficiencies greater than 85% have been achieved.