Optical integration and verification of LINC-NIRVANA

The LBT (Large Binocular Telescope) located in Mount Graham near Tucson/Arizona at an altitude of about 3200m, is an innovative project being undertaken by institutions from Europe and USA. The structure of the telescope incorporates two 8.4-meter telescopes on a 14.4 center-to-center common mount. This configuration provides the equivalent collecting area of a 12m single-dish telescope. LINC-NIRVANA is an instrument to combine the light from both LBT primary mirrors in an imaging Fizeau interferometer. Many requirements must be fulfilled in order to get a good interferometric combination of the beams, being among the most important plane wavefronts, parallel input beams, homotheticity and zero optical path difference (OPD) required for interferometry. The philosophy is to have an internally aligned instrument first, and then align the telescope to match the instrument. The sum of different subsystems leads to a quite ambitious system, which requires a well-defined strategy for alignment and testing. In this paper I introduce and describe the followed strategy, as well as the different solutions, procedures and tools used during integration. Results are presented at every step.