Framework for the precision control of a laser beam

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Dr. Simon Csaba
Department of Telecommunications and Media Informatics

In this thesis first the CLIC concept is introduced explaining the need for a new linear collider. The concept of two beam acceleration is described: the drive beam interleaving with delay loops, and the specific time structure of the electron beam needed for this. The purpose of CTF3 and the advantages of a photo injector as an electron source for the drive beam is explained.

A great advantage of the photo injector is that the special time structure required in the electron beam can be created in the laser beam. The fiber optic system at the head of the laser used to create the required time structure is described. This process is called phase-coding. The phase-coding requires the accurate adjustment of a delay line, and an optical attenuator, as these settings effect the timing accuracy and amplitude stability of the phase-coded beam.

A measurement method to determine the accuracy of the delay and amplitude balance is required for the adjustment of this delay and attenuation. Two methods are proposed: a frequency domain method using a spectrum analyzer and a time domain method using an oscilloscope.

Extensive measurements with both methods were carried out. Both methods proved to be accurate ways of determining the accuracy of the delay and amplitude balance. The frequency domain method is well suited for an easy setup of the system, and the time domain method was used for verification. Further developments are proposed to ensure that the timing and amplitude accuracy of the phase-coding is optimal.


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