Matthias Felber

Long-term stable microwave signal extraction from mode-locked lasers

Long-term synchronization [13-fs (10 Hz-10 MHz), <50 fs (for one hour)] between two 10.225-GHz microwave signals at +10 dBm referenced to a 44-MHz repetition rate mode-locked fiber laser is demonstrated using balanced optical-microwave phase detectors.

The FLASHForward facility at DESY

The FLASHForward project at DESY is a pioneering plasma-wakefield acceleration experiment that aims to produce, in a few centimetres of ionised hydrogen, beams with energy of order GeV that are of quality sufficient to be used in a free-electron laser. The plasma is created by ionising a gas in a gas cell with a multi-TW laser system. The plasma wave will be driven by high-current-density electron beams from the FLASH linear accelerator. The laser system can also be used to provide optical diagnostics of the plasma and electron beams due to the <30 fs synchronisation between the laser and the driving electron beam. The project will explore both external and internal witness-beam injection techniques. The operation parameters of the experiment are discussed, as well as the scientific programme.

Improved fiber-optic link for the phase reference distribution system for the TESLA technology based projects

The UV Free-Electron Laser (UVFEL) [1], The X-Ray Free-Electron Laser (XFEL) [2] and The International Linear Accelerator (ILC) [9] projects will require phase synchronization of various RF frequency subsystems on kilometer distances with accuracy better than 1ps. To fulfill these requirements, a phase reference distribution system concept was proposed and a prototype was developed for tests in the TESLA Test Facility 2 (TTF2). An important part of the phase reference system is the fiber-optic phase stable, long distance link described in this paper. An interferometrical scheme with feedback on phase, suppressing long term phase drifts induced by temperature changes was developed and tested in laboratory and under accelerator conditions. A motorized optical delay line was used in the system to compensate for phase errors. Described are error considerations and most important project issues like the hardware development and the real time phase controller software. The presented measurement results satisfy the design requirements. Experience gained during the experiments yielded proposals for system improvements.

Design and Operation of the Integrated 1.3 GHz Optical Reference Module with Femtosecond Precision

In modern Free-Electron Lasers like FLASH or the European XFEL, the short and long-term stability of RF reference signals gains in importance. The requirements are driven by the demand for short FEL pulses and low-jitter FEL operation. In previous publications, a novel, integrated Mach-Zehnder Interferometer based scheme for a phase detector between the optical and the electrical domain was presented and evaluated. This Laser-to-RF phase detector is the key component of the integrated 1.3GHz Optical Reference Module (REFM-OPT) for FLASH and the European XFEL. The REFMOPT will phase-stabilize 1.3GHz RF reference signals to the pulsed optical synchronization systems in these accelerators. Design choices in the final hardware configuration are presented together with measurement results and a performance evaluation from the first operation period in the European XFEL.

Custom Optomechanics for the Optical Synchronization System at the European XFEL

Free-electron-lasers like the upcoming European XFEL demand highly reliable optical synchronization in the range of a few femtoseconds. The well-known optical synchronization system at FLASH had to be reengineered to meet XFEL requirements comprising demands like ten times larger lengths and raised numbers of optically synchronized instruments. These requirements directly convert to optomechanical precision and have yielded in a specialized design accounting for economical manufacturing technologies. These efforts resulted in reduced spatial dimensions, improved optical repeatability, maintainability and even reduced production costs. To account for thermal influences the heart of the optical synchronization system is based on an optical table made out of SuperInvar. To fully exploit its excellent thermal expansion coefficient, mechanical details need to be taken into account. This work presents the design and its realization of the re-engineered optomechanical parts of the optical synchronization system, comprising mounting techniques, link stabilization units and optical delay lines for high drift suppression.

Influence of erbium-doped fiber amplifiers on the timing stability of optical pulse trains

The influence of an erbium-doped fiber amplifier on the timing stability of an optical pulse train was characterized with balanced optical cross-correlation. Under optimized conditions, an added timing jitter of 0.5 fs was achieved.

Long-Term Stable Microwave Signal Extraction from Mode-Locked Lasers

Long-term synchronization [13-fs (10 Hz-10 MHz), <50 fs (for one hour)] between two 10.225-GHz microwave signals at +10 dBm referenced to a 44-MHz repetition rate mode-locked fiber laser is demonstrated using balanced optical-microwave phase detectors.

Fiber-optic link for the RF phase reference distribution system for the XFEL and TESLA projects

The UV Free-Electron Laser (UVFEL) and The TeV-Energy Superconducting Linear Accelerator (TESLA) projects will require phase synchronization of 0.1 ps short term (millisecond), 1 ps short term (minutes) and 10 ps long term (days). The stringent synchronization requirement of 10fs was given for the X-Ray Free- Electron Laser (XFEL). To fufill this requirement the XFEL may use a fiber laser as reference generator. But this requirement applies for a special location only, therefore the RF phase reference distribution system developed UVFEL and TESLA will also be used in the XFEL. The RF phase reference distribution system must deliver phase stable signals to hundreds of stations over a length of 33 km. Long, optical fiber based links are planned to be an important part of the entire distribution system. This paper describes the concept of a long optical link, with a feedback system suppressing long term drifts of the RF signal phase. Stability requirements are given and most important design issues affecting system performance are discussed. Finally, an experimental setup and measurement results demonstrating system performance is shown.