LBNL, Berkeley, California
SLAC, Menlo Park, California
The scientific potential of femtosecond x-ray pulses at linac-driven FELs such as the LCLS is tremendous. Time-resolved pump-probe experiments require a measure of the relative arrival time of each x-ray pulse with respect to the experimental pump laser. In order to achieve this, precise synchronization is required between the arrival time diagnostic and the laser, which are often separated by hundreds of meters. We describe an optical timing system based on stabilized fiber links which has been developed for the LCLS to provide this synchronization. Preliminary results show synchronization of the synchronization signals at the sub-10 fsec level and overall synchronization of the x-ray and pump laser of <40 fsec. We present details of the implementation and LCLS and potential for future development.
LBNL, Berkeley, California
Stabilized optical fiber links have been under development for several years for high precision transmission of timing signals for remote synchronization of accelerator and laser systems. In our approach, a master clock signal is modulated on an optical carrier over a fiber link. The optical carrier is also used as the reference in a heterodyne interferometer, which is used to precisely measure variations, mainly thermal, in the fiber length. The measured variations are used to correct the phase of the transmitted clock signal. We present experimental results showing sub-10 fsec relative stability of a 200 m link, and sub-20 fsec stability of a 2.2 km link.
LBNL, Berkeley, California
High precision phase measurement is important for many areas of accelerator operation. In a heterodyne digital receiver, one source of phase error is due to the thermal variation of the input stage. We have developed a technique to calibrate this drift. A CW calibration signal is sent through the same components together with the RF signal to measure and compensate the component drift. At intermediate frequency (IF), we use FPGA based digital signal processing to measure and reconstruct the RF signal after applying appropriate correction. Using this technique, we can measure the phase of a 2856 MHz signal with an accuracy of 15 mdeg. We describe how this is approach is applied to the femto-second timing distribution system.