Final Report on the Joule-Scale Experimental Demonstration
We describe the final results of the High Power Laser Pulse Recirculation project. We have developed and implementing a novel technique for picosecond, Joule-class laser pulse recirculation inside a passive cavity. The aim of this project was to develop technology compatible with increasing the efficiency of Compton based light sources by more than an order of magnitude. In year 1 of the project, we achieved a greater than 40 times average power enhancement of the mJ-scale laser pulses inside a passive cavity with internal focus. In year 2, we demonstrated recirculation of lasers pulses with energies up to 191 mJ at 532 nm, at a repetition rate of 10 Hz, and a pulse duration of 20 ps. In this high energy regime, we achieved up to 14 times average power enhancement inside the cavity. This enhancement factor is compatible with the new X-band based mono-energetic gamma-ray machine, Velociraptor, being constructed at LLNL. The demonstrated cavity enhancement is primarily limited by the poor spatial beam quality of the high power laser beam. We expect a nearly diffraction limited laser beam to achieve 40 times or better cavity enhancement, as demonstrated in low energy experiments in FY-07. The two primary obstacles to higher average brightness and conversion efficiency of laser pulse energy to gamma-rays are the relatively small Compton scattering cross-section and the typically low repetition rates of Joule-class interaction lasers (10 Hz). Only a small fraction (10{sup -10}) of the available laser photons is converted to gamma-rays, while the rest is discarded. To significantly reduce the average power requirements of the laser and increase the overall system efficiency, we can recirculate laser light for repeated interactions with electron bunches. Our pulse recirculation scheme is based on nonlinear frequency conversion, termed recirculation injection by nonlinear gating (RING), inside a passive cavity. The main objectives of the two year project were: (1) Validate the concept of RING pulse trapping and recirculation technique. Completed Sep. 07 (2) Develop cavity designs compatible with a laser-electron Compton light source. Completed January 08. (3) Demonstrate trapping and recirculation of laser pulses suitable for high brightness gamma-ray generation. Completed Aug. 08 Our project has established RING as a viable technology for enhancing Compton scattering based gamma-ray generation. With sufficient funding we can implement pulse recirculation on the next generation Mono-energetic Gamma-Ray machine under construction at LLNL.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 945501
- Report Number(s):
- LLNL-TR-407621; TRN: US0901205
- Country of Publication:
- United States
- Language:
- English
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