Latest optical and mechanical upgrades in the GREGOR Infrared Spectrograph for simultaneous spectral observations

The GREGOR Infrared Spectrograph (GRIS) can perform spectropolarimetric observations in the infrared. The spectrograph has a Czerny-Turner design and offered traditional long-slit observations since 2014. Later on, in 2018, it was upgraded with an Integral Field Unit (IFU) based on a slicer mirror, which has slicers of 100-μm width. The latter option makes GRIS a unique instrument in solar physics that, after more than 10 years of operation, is still at the forefront of the field, particularly in the infrared. A third upgrade took place in 2021, where optomechanical, control and software improvements have been conducted to introduce new optical channels that operate below 1 μm. These new spectral channels allow simultaneous observations with the previous infrared camera. Between these improvements, a new diffraction grating was installed to enable multi-wavelength configurations with high scientific potential. This new diffraction grating will be interchangeable with the previous one, offering flexibility between spectral resolution, simultaneity, and spectral coverage. Additionally, two more IFUs will be offered to the community. One IFU with a 70-μm width slicer mirror that has already been manufactured and tested at the telescope, and the second with a 35-μm width slicer mirror that is currently at development status. The three IFUs will be interchangeable and offer three different spatial resolution modes and fields of view. This work presents the final optical configuration of the upgraded GRIS and the installation procedure of the most recent upgrades.