Research Topic

Development of a Femtosecond Bunch Arrival Time Monitor System


The Free Electron Laser in Hamburg (FLASH) is equipped with Bunch Arrival time Monitors (BAM), which provide for a time resolution of less than 10 fs for bunch charges higher than 0.2 nC. The timing information is obtained by mixing the pickup signal with the pulses of a reference laser in an Electro Optical Modulator (EOM). This information is coupled back to the first accelerating module, for stabilizing the arrival time jitter of the electron bunches to less than 25 fs. The sensitivity of the measurement system is defined by the slope of the pickup signal at the zero crossing and scales close to linear with the bunch charge. For future experiments lower bunch charges down to 10 pC are of interest. In this case the requirements on the time resolution will no longer be fulfilled. The slope of the pickup can be increased either by increasing the output signal voltage or its frequency. Due to a technical limitation of the maximum signal voltage a new pickup has to be developed which has a bandwith of 40 GHz or higher.

Development of new Pickup

The first part of this topic focuses on the development of a new pickup system. In the first step new pickup designs are simulated and compared with the currently installed pickup system. In cooperation with DESY in Hamburg and the institute of Microwave Engineering and Photonics at the TU Darmstadt, one of the new pickup designs was chosen based on the criteria of the signal shape, the producibility, and the production cost.

The chosen new pickup was built and installed at the particle accelerator FLASH in Hamburg.

Development of a Front-end Prototype for the new Pickup

The measurement for the new pickup requires a new read out front-end with a bandwidth up to 40 GHz. The core of the measurement system are electro-optical modulators (EOMs). These EOMs modulate short laser pulses, which are generated by a master laser oscillator system. In this step of the research topic new EOM candidates are measured and a new prototype of the front-end was built. Also some test measurements with the front-end prototype were conducted at FLASH.

Key Research Area

Accelerator physics, electromagnetic fields, electro-optical systems


Alexander Kuhl


Dolivostr. 15

D-64293 Darmstadt



+49 6151 16 - 24401 or 24402


+49 6151 16 - 24404




kuhl (at) gsc.tu...

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