Implementing Digital Feedback Controls for the Multiple Simultaneous Ring Cavities in the FASOR-X Systems

摘要

Precision tuned high power (50W) 589nm generation for use in laser sodium guidestar generation is a key capability in today's modern adaptive optical systems. The approached used is Sum-Frequency Generation (SFG) of 1319nm and 1064nm lines of Nd:YAG in an LBO crystal. High power narrow line sources are not commercially available, so low power narrow-band NPRO sources are mated with resonantly tuned high power ring lasers to achieve high power pumps. Efficient conversion of 589nm requires high pump intensities within the LBO crystal, therefore a doubly-resonant ring cavity is used. Four implementations of the Pound-Drever-Hall method are applied to achieve these. Finally, precision wavelength tuning is required to generate the correct wavelength as measured by a Wavemeter and verified by a low pressure Na-cell. These multiple control loops are all interconnected, to some degree, with various physical requirements, constraints, and caveats. Like any worthwhile project, the systems integration of the control systems has been an educational endeavor.