Experimental analysis on calibration of instrument broadening in a lidar system with Fabry-Perot etalon

A Brillouin lidar system based on a Fabry-Perot (F-P) etalon and intensified charge coupled device (ICCD) is widely used in measuring ocean physical properties. In previous signal detecting methods, the resolution of the obtained Brillouin spectrum is the major limitation on measurement accuracy of the Brillouin spectrum. The effect due to the instrument of the F-P etalon is relatively minor and typically neglected. However, because methods for obtaining a high resolution spectrum have greatly improved the spectral resolution, the instrument broadening has become the major error source and should be taken into consideration in the measurement. Instrument broadening is a common topic and has been widely researched. Unfortunately, for applications involving a high resolution spectrum, no detailed study has analyzed the performance of the methods for calibrating the broadening with high resolution experimental data. In this paper, the capability and the time costs of methods for reducing the broadening effect are evaluated for a high resolution spectrum obtained from underwater experiments. We also discuss in detail the implementation of the methods. Experimental results show that the three methods considered can effectively calibrate the broadening effect and improve the measurement accuracy from tens of MHz to MHz magnitude. Considering the similar performance of the methods, one method that is sufficient for online measurement is recommended as the optimal method.