Cross-disperser gratings

cross-disperser wheel
(click for larger)

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.

Polarimeter assembly

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.