One of the major aspects of the CRIRES+ upgrade can be seen in this image. It shows the cross-disperser wheel that holds six reflective gratings, one for each of the near-infrared bands YJHKLM. Visible are the ones for K, L and M bands. The wheel will rotat to choose the band to be observed. The light that reflects off the grating will be dispersed by wavelength before it reaches the main grating with much higher resolution.
Since the direction of cross-dispersion is perpendicular to the main dispersion, we can fit 9 spectral orders onto the detectors (see simulations), compared to a single one before. The simultaneous wavelength coverage and efficiency of CRIRES+ will therefore go up by about an order or magnitude.
Magic is happening at Uppsala university, where we have now all the optical/mechanical components for the CRIRES+ polarimeter, as well as all the components for the lab: IR camera, monochromator, and IR light sources among other. We are now doing the assembly of the polarimeter, and we will test and characterize it right after to verify we comply with the specification of the instrument.
The image above shows the now assembled turret that will hold the polarizing beam splitters. It rotates around it central vertical axis, as seen in the video below. Additional motors on the sides will allow us to exchange the two beams with each other, by rotating the optical elements. The turret is less than 15 cm in diameter and will soon be transported from Uppsala to Garching for more testing and integration.
This short video shows Alexis Lavail demonstrating the turret rotation, together with a short explanation by Nikolai Piskunov: