Multi-Fourier Transform Interferometry

Double Fourier Spatio-Spectral Interferometry is the application of a Fourier-transform spectrometer (FTS) to aperture synthesis interferometry. This technique was proposed for the near IR regime by Itoh and Ohtsuka (1986) with a single-pupil interferometry approach, and by Mariotti and Ridgway (1988) with multi-pupil interferometry for high spatial resolution. 

Leisawitz et al. (2003) proposed an extension of the FOV by using a focal plane detector array for optical wavelengths, technique called Wide-Field Imaging Interferometry. However, direct detector arrays in the Far Infrared are still expensive and a similar approach is not straightforward. 

Ohta et al. (2006) theoretically proposed to apply a Martin-Puplett-type Fourier-transform spectrometer to the aperture synthesis system in millimeter and submil-limeter waves. They succeeded in proving that this system is capable of performing broadband imaging observations (Ohta et al. 2007). Also a laboratory prototype spectral-spatial interferometer (Chap. 3) has been constructed to demonstrate the feasibility of the double-Fourier technique at far infrared (FIR) wavelengths (0.15-1 THz) by Grainger et al. (2012). 

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In Sect. 2.2 the fundamentals of Stellar Interferometry are shown. Starting with the Young s double slit experiment the interferometric observables are explained, this is, the complex visibility function. The data synthesis relevant to the work of this thesis is then presented. Finally, in Sect. 2.3 the concept of Multi-Fourier Transform Interferometry is developed. 

To achieve the angular resolution and sensitivity required for FIRI, one can use the so-called Spectral-Spatial Interferometry, Double Fourier Modulation, multi-Fourier Transform Spectroscopy or Double Interferometry (Mariotti and Ridgway 1988 Ohta et al. 2006, 2007), as a result of a combination of two well-known techniques Stellar Interferometry and Fourier Transform Spectroscopy. 

The fundamentals of Spectro-Spatial Interferometry (Mariotti and Ridgway 1988), also called Double Fourier Modulation (DFM) or Multi-Fourier Transform Spectroscopy (Ohta et al. 2007, 2006), are presented here and provide the background for the understanding of the following chapters. 

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