An Absolute Optical Frequency Reference Based on Doppler-Free Spectroscopy of Molecular Iodine Developed for Future Applications in Space

Optical frequency references are a key technology for a variety of future space missions dedicated to fundamental physics, Earth observation and navigation & ranging. We realized an ultra-stable optical frequency reference on engineering model (EM) level utilizing Doppler-free spectroscopy of molecular iodine near 532nm. A frequency stability of about 1⋅10-14 at an integration time of 1 s and below 5⋅10-15 at integration times between 10 s and 100 s was achieved. These values are comparable to the currently best laboratory setups. The EM setup uses a 380 x 180 x 40 mm3 baseplate made of fused silica where the optical components are joint using a specific assembly-integration technology. Special emphasis is put on compactness and highest mechanical and thermal stability. The custom-made compact and robust multi-pass gas cell was developed in collaboration with the Institute of Scientific Instruments (Brno) of the Academy of Sciences of the Czech Republic. The EM setup was subjected to thermal cycling and vibrational testing. We report on the current status of the setup and highlight potential applications in future space missions.