06 Beam Instrumentation, Controls, Feedback, and Operational Aspects
T25 Lasers
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WEPAL041 FPGA Based Optical Phase Control for Coherent Laser Pulse Stacking 2265
 
  • Y. Yang, L.R. Doolittle, Q. Du, G. Huang, W. Leemans, R.B. Wilcox, T. Zhou
    LBNL, Berkeley, California, USA
  • A. Galvanauskas
    University of Michigan, Ann Arbor, Michigan, USA
 
  Coherent temporal pulse stacking combines the energy from a train of pulses into one pulse through a series of optical cavities. To stabilize the output energy, the cavity roundtrip phases must be precisely locked to particular values. Leveraging the LLRF expertise we have for conventional accelerators, a FPGA-based control system has been developed for optical cavity phase control. A phase measurement method, ''Modulated Impulse Response'', has been developed and implemented on FPGA. An experiment demonstrated that it can measure and lock the optical phases of four stacking cavities, leading to combination of 25 pulses into one pulse with 1.5 % RMS stability over 30 hours.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL041  
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THPML099 Phase Extraction and Stabilization for Coherent Pulse Stacking 4895
SUSPL060   use link to see paper's listing under its alternate paper code  
 
  • Y.L. Xu, W.-H. Huang, C.-X. Tang, L.X. Yan
    TUB, Beijing, People's Republic of China
  • L.R. Doolittle, Q. Du, G. Huang, W. Leemans, D. Li, R.B. Wilcox, Y. Yang, T. Zhou
    LBNL, Berkeley, California, USA
  • A. Galvanauskas
    University of Michigan, Ann Arbor, Michigan, USA
 
  Funding: This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under Contract DE-AC02-05CH11231.
Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy and high average power. We model the CPS as a digital filter in the Z domain, and implement two deterministic algorithms extracting the cavity phase from limited data where only the pulse intensity is available. In a 2-stage 15-pulse CPS system, each optical cavity is stabilized at an individually-prescribed round-trip phase with 0.7 deg and 2.1 deg RMS phase errors for Stage 1 and Stage 2 respectively. Optical cavity phase control with nm accuracy ensures 1.2% intensity stability of the stacked pulse over 12 hours.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML099  
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THPML115 Introduction of the Laser Intensity Measurement System for the FELiChEM 4936
 
  • F.L. Gao, L.T. Huang, P. Lu, B.G. Sun, J.G. Wang, F.F. Wu, Y.L. Yang, T.Y. Zhou
    USTC/NSRL, Hefei, Anhui, People's Republic of China
 
  The FELiChEM is a new infrared free electron laser (IR-FEL) facility, which is being built in the National Synchrotron Radiation Laboratory (NSRL) in Heifei, China. The facility will provide continuously tunable pulsed laser radiation covering the mid-infrared (MIR) wavelength range from 2.5 to 50μm and the far-infrared (FIR) range from 40 to 200μm. The output macro pulsed laser width is 5-10μs and pulsed laser power is 2-10kW. In order to evaluate pulsed laser saturation time and FEL optical cavity losses, the rise time and fall time of macro pulsed laser need to be measured. Laser intensity measurement system for the FELiChEM is being designed. This system is composed of optical system, pyroelectric detector and electronics. Each module will be described in detail in this paper. The laser intensity measurement system was tested under offline and online conditions. The results showed that pulsed laser of 10μs width can be measured and the design requirement can be met with this system.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML115  
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