The Jefferson Lab High Power Broadband THz Facility
Jefferson Lab operates a broadband terahertz (THz) facility, whose light is generated by 300 fs FWHM 135 pC bunches of electrons at an energy of 125 MeV as they traverse a magnetic compression chicane prior to entering the optical cavity of the Jefferson Lab Free Electron Laser (FEL)[1-3]. The repetition rate of the electron bunches, and hence that of the light pulses, can be as high as 75 MHz continuous. Approximately 1 microJoule of energy is emitted for each pulse, which implies an average power of up to 75W, a peak power of several MW and electric fields of MV/m. Niche applications of this unique source are pump-probe dynamics, both in and out of equilibrium, and large-scale imaging. The beamline itself is designed to deliver an f/8 beam 2mm vertical × 3mm horizontal in size and 60% vertically polarized from a subtended angle of ~200 milliradians horizontal by ~135 milliradians vertical in the accelerator. The first mirror is copper-braid cooled. The philosophy of the optical design is to use a relay optics configuration to transport the beam via reflection off metal mirrors through a series of focal points, with the final one being at a diamond window. The optical scheme was developed using the Synchrotron Radiation Workshop (SRW)[4]. This code performs a full calculation of the electric field from a relativistic electron. It does not handle multiparticle coherent enhancement[5], but it is significantly different from all the other synchrotron radiation calculations because it retains a term called the Coulomb term in which the electric field falls off as 1/R2. In addition to calculating the electric field and the intensity, the code also allows one to propagate the field through the optical focusing elements and apertures. The beam exiting the final diamond window in the THz user lab passes into a series of vacuum chambers with considerable flexibility for attenuation, collimation, and/or beam splitting for imaging, spectroscopy and 2 photon pump-probe measurements. In this talk we will discuss the details of the philosophy, optical design and operating experience of this facility and also present ideas for discussion. We deeply appreciate the excellent support of our colleagues without which these facilities would not have been built and operated. This work was supported by the U.S. Dept. of Energy under contract DE-AC05-06-OR23177, and the Commonwealth of Virginia. The FEL facility is supported by the Office of Naval Research. 1. S. V. Benson et al, ?The VUV/IR/THz Free Electron Laser Program at Jefferson Lab?, Nucl. Instr. and Meth. A649 9 (2011). 2. G.L. Carr, M.C. Martin, W.R. McKinney, K. Jordan, G.R. Neil and G.P. Williams ?High Power Terahertz Radiation from Relativistic Electrons?, Nature 420 153-156 (2002). 3. J.M. Klopf et al. ?The Jefferson Lab high power THz user facility?, Nucl. Instrum. Methods A582, 114-116 (2007). 4. O. Chubar, P. Elleaume, "Accurate And Efficient Computation Of Synchrotron Radiation In The Near Field Region", proc. of the EPAC98 Conference, 22-26 June 1998, p.1177-1179. 5. C. J. Hirschmugl, M. Sagurton and G. P. Williams, ?Multiparticle coherence calculations for synchrotron radiation emission? Physical Review A44, 1316 (1991).
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Nuclear Physics (NP)
- DOE Contract Number:
- AC05-06OR23177
- OSTI ID:
- 1994542
- Report Number(s):
- JLAB-FEL-12-1687; DOE/OR/23177-6934
- Resource Relation:
- Conference: Workshop on THz sources for time resolved studies of matter, Argonne National Lab, July 30, 2012
- Country of Publication:
- United States
- Language:
- English
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