Far-Infrared Interferometeric Telescope Experiment (FITE): sensor optics

We have developed a sensor optical system for the Far Infrared Interferometric Telescope (FITE). The spatial resolution of FITE is expected to be 2.5 arcseconds. In order to derive the spatial extent of target objects, the visibility of interference fringes has to be measured precisely. For this purpose, we constructed the focal plane assembly of the FITE interferometer with the sensor optics. The focal plane is the entrance focus of the sensor optics. A far-infrared (FIR) array detector is installed on the final focal plane of the sensor optics. Its camera optics has F/106 beam for each beam of the interferometer. The PSF is dominated by diffraction, and its size corresponds approximately to the array size so that the fringe pattern can be measured by the array in real time. This system employs of two IR detectors and an optical CCD. The FIR detector has a format of 1.5mm ×15 pixels. In addition to the FIR array detector, we have a mid-IR detector and an optical CCD. They are also installed on the final focal plane of the sensor optics. These two detectors are used for the precise alignment of the interferometer optics.