Multi-functional immersion grating by homemade freeform cutting machine

The application fields of Infrared spectroscopy are extremely wide from matter analysis of organisms to environmental observation. In wide-band spectroscopy, a pair of two different dispersive gratings is used. One is a high-order high dispersive grating according to the bandwidth of the detector; other is a low dispersive grating that separates the overlapping order. In this work, a low dispersion grating was fabricated on the incident surface of a conventional immersion grating to manufacture the world's first multifunctional Germanium immersion grating having two gratings in one device. Positioning accuracy with respect to three-dimensional space with our homemade cutting machine has an extremely good accuracy of less than 3nm RMS locally and less than 15nm RMS globally. The grating surface roughness is less than 3nm RMS. We introduce next-generation diffractive grating processing technology with extremely high freedom.