2016 Scientific Ballooning Technologies Workshop Title Optical Design of a Balloon-borne Interferometer ‘BETTII’ Author Arnab Dhabal (University of Maryland) Abstract Balloon Experimental Twin Telescope for Infra-red Interferometry (BETTII) is a “double-Fourier” Michelson interferometer combining spatial interferometry with Fourier Transform Spectroscopy in the FIR wavelengths (30-90um) to study clustered star forming regions. It has an 8-m baseline with 0.5-m light collecting siderostats at the two ends. The light from the two arms is combined inside a cryostat and focused onto detectors. An important challenge for this interferometer is to maintain the wavefronts until beam combination. I present the opto-mechanical design of BETTII, with emphasis on the delay line mechanisms that are used for correcting for optical path differences (OPD) between the two arms, and for introducing a systematic OPD to produce interferograms at the detector.

2016balloontech.umn.edu