  For astronomical instruments, accurate knowledge of the optical pointing and
coupling are essential to characterize the alignment and performance of
(sub-)systems prior to integration and deployment. Ideally, this requires the
phase response of the optical system, which for direct (phase insensitive)
detectors was not previously accessible. Here we show development of the phase
sensitive complex beam pattern technique using a dual optical source heterodyne
technique for a large field of view Microwave Kinetic Inductance Detector
camera at 350 GHz. We show here how you can analyze the measured data with
Fourier optics, which allows integration into a telescope model to calculate
the on sky beam pattern and telescope aperture efficiency prior to deployment
at a telescope.
