An achromatic Michelson stellar interferometer

Abstract

Amplitude stellar interferometry systems are often limited by signal-to-noise ratio. When the limiting noise is photon noise it is possible to increase the signal-to-noise ratio simply by increasing the observation time. When the source signal is extremely faint, the source signal may be overwhelmed by noises associated with the detection system. In these cases it is not possible to get an acceptable signal-to-noise ratio by increasing the observation time. It is for these faint object observations that the achromatic Michelson stellar interferometer (AMSI) is proposed. The AMSI uses N sub-systems, each sub-system being of the same design as a conventional Michelson stellar interferometer (MSI). The light from these N sub-systems is combined in such a way so as to produce a single set of "white light" fringes. By increasing the signal by a factor of N, the AMSI produces a significant increase in signal-to-noise ratio. This dissertation first presents the theory behind the conventional MSI. Results are given from tolerancing the conventional MSI. The tolerancing is performed both with a computer model and with parallel analytical calculations. A chart which summarizes the tolerance results is presented near the end of Chapter 4. The theory behind the AMSI is stated along with the limitations of this method. A method for extending the AMSI through spectral multiplexing is also given. Tolerancing of the AMSI is also performed, again using both a computer model and parallel calculations. The AMSI is found to provide an increase in detectability of faint sources provided that it can be supplied with an adequate fringe-locking system or used in a space-based environment.