Frequency-Stable Laser Systems for Space

JOKARUS experiment on sounding rocket successfully completed. The foundation stone for laser distance measurements with the highest precision and pioneer for optical satellite systems for navigation.

laser systems
JOKARUS payload for the first optical frequency standard based on molecular iodine in space. | © HU Berlin / Franz Gutsch

For the first time, a frequency reference based on molecular iodine in space was successfully demonstrated! What sounds a bit like science fiction is an important step towards laser interferometric distance measurements between satellites or for future global navigation satellite systems based on optical technologies. The frequency reference tests were carried out on 13 May on board the TEXUS54 sounding rocket. A compact laser system, which was largely developed by HU Berlin and the Ferdinand Braun Institute, demonstrated its suitability for space.

In the JOKARUS experiment (Iodine comb resonator under weightlessness), an active optical frequency reference based on molecular iodine in space was qualified for the first time. The results are an important milestone on the way to using optical watches in space. Such clocks are required, inter alia, satellite-based navigation systems that provide data for accurate positioning. They are also indispensable for fundamental physical investigations, such as the detection of gravitational waves or for measuring the gravitational field of the earth.

The experiment demonstrated the automated frequency stabilization of a frequency-doubled 1064 nm extended cavity diode laser (ECDL) on a molecular transition in iodine. Thanks to integrated software and appropriate algorithms, the laser system worked completely independently. For comparison purposes, during the same space flight, a frequency measurement was performed with an optical frequency comb in the separate FOKUS II experiment.

This know-how is in the compact diode laser system

The JOKARUS payload was developed and set up under the direction of the Humboldt University of Berlin (HU Berlin) as part of the Joint Lab Laser Metrology. The Joint Lab is operated jointly by the Ferdinand Braun Institute, Leibniz Institute for High Frequency Technology (FBH) and the HU Berlin and pools the know-how of both institutions in the field of diode laser systems for space applications. A quasi-monolithic spectroscopy module was provided by the University of Bremen, while the operating electronics are from Menlo Systems.

The heart of the system is a microintegrated ECDL MOPA with an ECDL as a local oscillator (Master Oscillator, MO) and a ridge waveguide semiconductor amplifier as a power amplifier (PA), which was developed and realized at the FBH. The 1064 nm laser module is fully encapsulated in a 125 x 75 x 22.5 mm small package and delivers an optical power of 570 mW within the linewidth of the free-running laser of 26 kHz (FWHM, 1 ms measurement time). By means of a polarization-preserving, optical single-mode fiber, the laser light is first divided into two paths, modulated, frequency-doubled and processed for Doppler-free saturation spectroscopy. The technology development in JOKARUS funded by the German Aerospace Center (DLR) is based on the earlier FOKUS, FOKUS reflight, missions

Source : Forschungsverbund Berlin e. V.