An absolute optical frequency reference for space

A variety of future space missions rely on the availability of high-performance optical frequency references with applications in fundamental physics, geoscience, Earth observation and global satellite navigation systems (GNSS). Examples are the gravitational wave detector LISA (Laser Interferometer Space Antenna), the Earth gravity mission NGGM (Next Generation Gravity Mission) and missions, dedicated to tests of Special Relativity, e.g. by performing a Kennedy-Thorndike experiment testing the boost dependence of the speed of light. In this context, we developed optical frequency references based on Doppler-free spectroscopy of molecular iodine where compactness and mechanical and thermal stability are main design criteria. We demonstrated a frequency instability of 610-15 at 1 s integration time and 310-15 for integration times between 100 s and 1.000 s. Furthermore, a very compact spectroscopy setup was realized for the sounding rocket mission JOKARUS which was successfully flown in May 2018. In a current activity, an integrated high-performance iodine-based frequency reference is developed which serves as a demonstrator for future GNSS using optical technologies.