Thermal baffling of SPHERE IFS

IFS is one of the scientific channels of SPHERE, the new high contrast imager for the ESO VLT telescope. IFS is an integral field spectrograph for the near IR (up to 1.65 micron), using a Hawaii II detector. To simplify opto-mechanical design, IFS has no cold pupil. To reduce thermal background, a cold filter fabricated by JDSU has been placed about 30 mm in front of the detector. This filter allows reducing thermal background by more than a factor 10 4 . We describe the design and implementation of the baffling required for proper use of this system: this includes a combination of a cold and a warm baffles, and appropriate choices of the coatings of the surfaces. We present the laboratory results obtained, which show that this system has a thermal background below 10 e-/s/pixels in the SPHERE working conditions.