A radiation tolerant Erbium fiber based optical frequency comb has been developed and environmentally tested. The system remained operable after an accumulated dose of 1 kGy∗
. The underlying femtosecond fiber oscillator and Erbium fiber amplifiers have been manufactured from speciality doped fibers. The fiber optic system has been assembled and packaged using low outgassing components in a flight representative package before it was irradiated under active operation in two stages a 500 kGy. The accelerated ageing with dose rates of 10 mGy/s in water was tested using the calibrated Cobalt 60 source of the ESA-ESTEC facilities. The comb laser remained fully functional while the oscillator lost up to 30% of output power after the full exposure to the accumulated dose of 1 kGy. The fiber amplifiers lost 5-7% of output power.
Advanced radiation tolerant Erbium doped fibers have been developed surviving an accumulated dose of 1 kGy∗. Femtosecond fiber lasers and amplifiers manufactured from such fibers have been packaged and irradiated under active operation to test for accelerated ageing with dose rates up to 10 mGy/s using a Cobalt 60 source. The laser output power degraded by about 11% after exposure of a dose of 1 kGy. Compared to conventional Erbium fiber lasers this represents a significant improvement in radiation tolerance.
The far-infrared (FIR) regime is one of the few wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist yet. Also medium-term satellite projects like SPICA, Millimetron or OST will not resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited CO and especially from water lines would open the door for transformative science. These demands call for interferometric concepts. We present here first results of our feasibility study IRASSI (Infrared Astronomy Satellite Swarm Interferometry) for an FIR space interferometer. Extending on the principal concept of the previous study ESPRIT, it features heterodyne interferometry within a swarm of 5 satellite elements. The satellites can drift in and out within a range of several hundred meters, thereby achieving spatial resolutions of <0.1 arcsec over the whole wavelength range of 1–6 THz. Precise knowledge on the baselines will be ensured by metrology employing laser frequency combs, for which first ground-based tests have been designed by members of our study team. In this contribution, we first give a motivation how the science requirements translated into operational and design parameters for IRASSI. Our consortium has put much emphasis on the navigational aspects of such a free-flying swarm of satellites operating in relatively close vicinity. We hence present work on the formation geometry, the relative dynamics of the swarm, and aspects of our investigation towards attitude estimation. Furthermore, we discuss issues regarding the real-time capability of the autonomous relative positioning system, which is an important aspect for IRASSI where, due to the large raw data rates expected, the interferometric correlation has to be done onboard, quasi in real-time. We also address questions regarding the spacecraft architecture and how a first thermomechanical model is used to study the effect of thermal perturbations on the spacecraft. This will have implications for the necessary internal calibration of the local tie between the laser metrology and the phase centres of the science signals.
Photonic synthesis of radio frequency waveforms revived the quest for unrivalled microwave purity by its seducing ability to convey the benefits of the optics to the microwave world. In this contribution, we will present a high-fidelity transfer of frequency stability between an optical reference and a microwave signal via a low-noise fiber-based frequency comb and cutting-edge photo-detection techniques. We will show the generation of the purest microwave signal with a fractional frequency stability below 6.5×10-16 at 1 s and a timing noise floor below 41 zs Hz-1/2 (phase noise below -173 dBc Hz-1 for a 12 GHz carrier). This outclasses existing sources and promises a new era for state-of-the-art microwave generation. The characterization is achieved through a heterodyne cross-correlation scheme with lowermost detection noise. This unprecedented level of purity can impact domains such as radar systems, telecommunications and time-frequency metrology. The measurements methods developed here can benefit the characterization of a broad range of signals.
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