ABSTRACT
This chapter discusses some topics on light sources, such as optical coherence related to the size of light sources and their spectral properties. A consideration of light source is now applied to measure the angular diameter of stars, while its spectroscopic measurement method is known as the Fourier transform spectroscopy. The phase shift interferometry will be also discussed in relation with the Fourier transform spectroscopy and some fringe analysis techniques. The chapter presents the use of the Hilbert transform in the interferometric fringe analysis. In the case when the observation point one coincides with observation point two, the mutual coherence function becomes the auto-coherence function. Because of the correlation of a wave at a point in different times and a function depending on only the time difference, this is called temporal coherence. The degree of spatial coherence gives the size of the light source.
