A number of new techniques for studying the properties of interference fringes have been presented within this report. Those techniques which were tested experimentally performed reasonably satisfactorily. It is hoped that further experimental work can be done at COAST in the near future.

The phase tracking technique described in Section 4 was implemented in a simplified form, and performed reasonably successfully in the experimental tests discussed in Section 5. The principle problem discovered with tracking fake data was a tendency for the phase to jump erroneously by one cycle at the end of each sweep. It is likely that this is a consequence of the fact that the input data was split up into individual sweeps to simplify the data processing. A possible course of future study would involve testing the phase tracking procedure described in Section 4 without this simplification.

Similar phase jumps were also found with data taken in the COAST laboratory. It is likely that deviations in the delay-line motion away from an ideal sawtooth were partially to blame in this case. The use of accurate delay-line position data should allow this effect to be removed.

The position measurement system described in Section 6 proved very successful in experimental tests, and it is possible that this might eventually be implemented at the COAST telescope. Accurate measurement of the position of the fringe envelope could allow the motion of the fringe envelope to be actively tracked during long closure phase measurements. The system might also help in the initial detection and location of the fringe envelope, saving valuable observing time.

Section 8 highlights the systematic errors induced in closure phase measurements by optical dispersion in the incoming light beams. It is likely that this topic will require further study before the planned expansion of the array is implemented. Examples of some closure phase measurement techniques which are less affected by dispersion are shown in Section 9. It would be very interesting to test some of these techniques on real astronomical data, and attempt to evaluate the systematic errors and random errors in the resulting measurements.

An attempt at measuring the difference in the dispersion present in two light beams is presented in Section 10. The random errors in the measurement were relatively large, and future studies might be more successful if closure relations were invoked in such a way that the effects of atmospheric fluctuations were reduced.

I feel that I have been able to provide one or two useful contributions to the field of optical interferometry. I have found this project extremely interesting, and would be quite keen to follow up some of the suggestions for further study. The effect of atmospheric turbulence and optical dispersion on ground based interferometers has been an important area of research for many years. I anticipate that this will continue to be the case for many years to come.

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