The conceptional design of the proposed linear electron-positron collider TESLA is based on 9-cell 1.3 GHz superconducting niobium cavities with an accelerating gradient of E acc $ 25 MV͞m at a quality factor Q 0 $ 5 3 10 9 . The design goal for the cavities of the TESLA Test Facility (TTF) linac was set to the more moderate value of E acc $ 15 MV͞m. In a first series of 27 industrially produced TTF cavities the average gradient at Q 0 5 3 10 9 was measured to be 20.1 6 6.2 MV͞m, excluding a few cavities suffering from serious fabrication or material defects. In the second production of 24 TTF cavities, additional quality control measures were introduced, in particular, an eddy-current scan to eliminate niobium sheets with foreign material inclusions and stringent prescriptions for carrying out the electronbeam welds. The average gradient of these cavities at Q 0 5 3 10 9 amounts to 25.0 6 3.2 MV͞m with the exception of one cavity suffering from a weld defect. Hence only a moderate improvement in production and preparation techniques will be needed to meet the ambitious TESLA goal with an adequate safety margin. In this paper we present a detailed description of the design, fabrication, and preparation of the TESLA Test Facility cavities and their associated components and report on cavity performance in test cryostats and with electron beam in the TTF linac. The ongoing research and development towards higher gradients is briefly addressed.

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/01/2015 Terms of Use: http://spiedl.org/terms . #%'## #" "(/ (0 #-'( #))%"!!#"With a data rate of 5.6 Gbps the laser communication links reported here have been a milestone in the introduction of laser communication terminals to the space market. For the first time the major advantage of laser communication terminals compared to RF payloads -data rates larger than 1 Gbps -has been demonstrated on orbit. In terms of shortterm service realization the most imminent market applications are relay services (LEO-to-GEO-to-ground) to make the large data amount of LEO Earth observation satellites immediately available. DLR plans to utilize the laser communication capabilities for the TanDEM-X mission and took TESAT under contract to adapt the now successfully proven LEO-LEO laser communication terminals to LEO-to-GEO, GEO-GEO, and GEO-to-ground links. This GEOclass LCT is designed for up to 45,000 km distance at a maximum user data rate of 1.8 Gbps.The next figure (Fig. 8) shows the application for which TESAT has developed and currently builds laser communication terminals and a 600 Mbps Ka-band subsystem.

A free-space optical link based on homodyne BPSK (binary phase shift keying) has been established between two of the Canary islands, La Palma and Tenerife, to transmit 5.625 Gpbs across 142 km. This link verifies homodyne BPSK as a robust modulation scheme even for the transmission through the atmosphere.

Laser communication terminals based on homodyne BPSK are under in-orbit verification in LEO-to-ground and duplex LEO-LEO 5.65 Gbps links. With the LEO-to-ground link beacon-less acquisition has been verified as a reliable and quick acquisition procedure with acquisition times less than one minute.

We present a compact femtosecond nonlinear Yb:YAG thin-disk regenerative amplifier delivering pulses carried at a wavelength of 1030 nm with an average power of >200  W at a repetition rate of 100 kHz and an energy noise value of 0.46% (rms) in a beam with a propagation factor of M²<1.4. The amplifier is seeded with bandwidth-limited subpicosecond pulses without temporal stretching. We give estimates for the nonlinear parameters influencing the system and show that chirped mirrors compress the 2 mJ pulses to a near-bandwidth-limited duration of 210 fs.