Identify the origin of the residual spatial-resolution discrepancy
Identify the origin of the residual approximately 10–20% discrepancy in the measured spatial resolution at 10 MHz resolution bandwidth when the measured unmodulated beat spectrum is used as the effective filter function, including possible measurement bias and optical noise contributions.
References
A residual discrepancy of approximately 10 to 20% remained at RBW = 10 MHz even when the measured filter function was used. The measured unmodulated beat spectrum was narrower than the Voigt prediction over most of the measured frequency range, indicating that the difference cannot be explained solely by the nominal RBW or by the assumed Gaussian filter shape. The origin of the remaining discrepancy could not be identified within the present study. Possible contributions include measurement bias under the actual signal conditions and optical noise associated with the present configuration [10]. Further measurements of the individual beat components will be required to clarify this discrepancy.
The present experiments were performed with a single light source and evaluated $\Delta z$ at RBW = 1 and 10 MHz, so the predicted dependence on source linewidth and RBW has not yet been tested systematically over a wider parameter range. In particular, the effect of reducing $\delta \nu$ remains to be verified experimentally.