FOKUS

About the Research Program

Precise control over the frequency of light is a prerequisite for several future satellite missions. Only frequency combs can give the degree of control that would be necassary for optical atomic clocks in space for fundamental physics experiments or navigation, laser ranging based atmospheric trace gas detection, equivalence principle tests, gravimetry or formation flights. For space applications a small energy efficient, robust and 100% maintenance-free system with low power consumption is of course mandatory.

Within the FOKUS projects (FOKUS I, FOKUS Ib, FOKUS II), an optical frequency comb for sounding rocket flights is developed and the technological maturity of frequency combs for space applications is significantly increased.

Within the FOKUS I project, we have developed a fiber based optical frequency comb system and successfully demonstrated its performance in a microgravity environment. The comb was complemented with a precision spectroscopy experiment comprising a hybrid integrated distributed feedback (DFB) diode laser and a rubidium gas cell unit for Doppler-free spectroscopy. On April 23rd, 2015 the system was launched within the TEXUS 51 mission from the Esrange site in Kiruna, Sweden. It has been a huge success, enabling the comparison of a RF frequency standard and the rubidium stabilized optical line in a fully automated setup. The system had to withstand static accelerations up to 13 g during the start as well as shocks up to 30 g during reentry and landing. The frequency comb stayed fully operational during and after the flight.

A second flight of the optical frequency comb on TEXUS 53 is scheduled for November 22nd, 2015. For this flight several system improvements and additional optical interfaces have been implemented. During the six minutes sounding rocket flight, the comb will compare two optical frequencies and the RF frequency of a rubidium lamp powered clock. The two optical lines are cw lasers which have been realized by the project partners Humboldt University of Berlin, Ferdinand Braun Institute, University of Hamburg, and University of Mainz.

Within FOKUS II, we will build on our experiences of the first comb in space and significantly improve the technology towards even smaller volume and weight, higher energy efficiency, and higher performance. We aim for a sounding rocket flight where the comb will be operated under vacuum for the first time and fully automated determining the optical frequency of a cw laser without ambiguities.

This project is supported by German Aerospace Center (DLR) and funded by Bundesministerium für Wirtschaft und Energie (BMWi).