We present first, promising experiments with a novel, compact and simple Nd:YVO<sub>4</sub> slab laser with 12 W of 1.06 μm optical output power and a beam quality factor M<sup>2</sup> ∼ 2.5. The laser is made of a diffusion-bonded YVO<sub>4</sub>/Nd:YVO<sub>4</sub> composite crystal that exhibits two unique features. First, it ensures a one-dimensional heat removal from the laser crystal, which leads to a temperature profile without detrimental influence on the laser beam. Thus, the induced thermo-optical aberrations to the laser field are low, allowing power scaling with good beam quality. Second, the composite crystal itself acts as a waveguide for the 809 nm pump-light that is supplied from a diode laser bar. Pump-light shaping optics, e.g. fast- or slow-axis collimators can be omitted, reducing the complexity of the system. Pump-light redundancy can be easily achieved. Eventually, the investigated slab laser might be suitable for distortion-free high gain amplification of weak optical signals.
Tesat-Spacecom is currently building a set flight models of frequency stabilized lasers for the ESA Missions AEOLUS and LTP. Lasers with low intensity noise in the kHz region and analogue tuning capabilities for frequency and output power are developed for the on board metrology of the LTP project, the precursor mission for LISA. This type of laser is internally stabilized by precise temperature control, approaching an ALLAN variance of 10<sup>-9</sup> for 100 sec. It can be easily locked to external frequency references with <50kHz bandwidth. The Seed laser for the AEOLUS mission (wind LIDAR) is used as the master frequency reference and is stabilized internally by a optical cavity. It shows a 3* 10<sup>-11</sup> Allan variance from time intervals 1 sec - 1000 sec. Furthermore it is step-tunable for calibration of the receiver instrument with a speed of GHz / sec by a digital command interface. Performance and environmental test results will be presented.
Quantum optics  can be harnessed to implement cryptographic protocols that are verifiably immune against any conceivable attack . Even quantum computers, that will break most current public keys [3, 4], cannot harm quantum encryption. Based on these intriguing quantum features, metropolitan quantum networks have been implemented around the world [5-15]. However, the long-haul link between metropolitan networks is currently missing . Existing fiber infrastructure is not suitable for this purpose since classical telecom repeaters cannot relay quantum states . Therefore, optical satellite-to-ground communication [17-22] lends itself to bridge intercontinental distances for quantum communication [23-40].
The European Data Relay System (EDRS) relies on optical communication links between Low Earth Orbit
(LEO) and geostationary (GEO) spacecrafts. Data transmission at 1,8 Gbps between the S/Cs will be applied for
link distances up to 45000 km. EDRS is foreseen to go into operation in 2015. As a precursor to the EDRS GEO
Laser Communication Terminals (LCT), a LCT is embarked on the Alphasat GEO S/C, which was launched in
July 2013. Sentinel 1A is a LEO earth observation satellite as part of ESAs Copernicus program. Sentinel 1A
also has a LCT on board. In November 2014, the first optical communication link between a LEO and a GEO
Laser Communication Terminal at gigabit data rates has been performed successfully . Data generated by the
Sentinel 1A instrument were optically transferred to Alphasat. From Alphasat, the data were transmitted via Kaband
to a ground station. In the ground station, the original data were recovered successfully. So the whole chain
from LEO to ground was verified. Since then, many optical communication links between the Alphasat LCT and
the Sentinel 1A LCT were performed. During these tests, the acquisition and tracking performance was
investigated. The first communication links showed a very robust link acquisition capability and tracking errors
in the sub-μrad range. The communication link budget was verified and compared to the predictions, showing
excellent overall system behavior with sufficient margin to support future GEO GEO link applications.
The European Data Relay System (EDRS) relies on optical communication links between Low Earth Orbit (LEO) and geostationary (GEO) spacecrafts. Data transmission at 1.8 Gbps between the S/Cs will be applied. EDRS is foreseen to go into operation in 2015. As a precursor to the EDRS GEO Laser Communication Terminals (LCT), an LCT is embarked on the Alphasat GEO S/C. Sentinel 1A is a LEO earth observation satellite as part of ESAs Copernicus program and carries an LCT on board. Both the Alphasat and the Sentinel 1A LCT have completed their individual in orbit commissioning and a joint link commissioning phase, with first LEO to GEO optical communication links in 2014. In this presentation, the design principle of the LCT applied for EDRS will be investigated. The most recent results of the in-orbit link commissioning phase of the LCTs on board of Alphasat and Sentinel 1A will be presented.
A 5.6 Gbps optical communication link has been verified in-orbit. The intersatellite link uses homodyne BPSK (binary phase shift keying) and allows to transmit data with a duplex data rate of 5.6 Gbps and a bit error rate better than 10-9 between two LEO satellites, NFIRE (U.S.) and TerraSAR-X (Germany). We report on the terminal design and the link performance during the measurement campaign. As an outlook we report on the flight units adapted to LEO-to-GEO intersatellite links that TESAT currently builds and on plans to study GEO-to-ground links.
We report on the development of optical resonators operated at cryogenic temperature. a miniature monolithic quartz crystal ring resonator has been operated at liquid helium temperature with a finesse of 330 at the Nd:YAG wavelength 1064 nm. A 3-cm-long Fabry_Perot cavity with mirrors optically contacted to a hollow fused silica spacer has been used for the frequency stabilization of two diode-pumped Nd:YAG lasers. The cavity exhibited a finesses of 240,000 at liquid helium temperature. The root Allan variance of the beat signal of the two lasers locked to two transverse modes of the cryogenic optical resonator (CORE) was below 10 Hz for integration times up to 100 s. Requirements for reaching sub-Hz instability for long times are briefly discussed and it is pointed out that COREs have interesting applications in high-precision fundamental physics experiments.