A new THz/IR/UV photon source at Jefferson Lab is the first of a new generation of light sources based on an Energy-Recovered, (superconducting) Linac (ERL). The machine has a 160 MeV electron beam and an average current of 10 mA in 75 MHz repetition rate hundred femtosecond bunches.These electron bunches pass through a magnetic chicane and therefore emit synchrotron radiation. For wavelengths longer than the electron bunch the electrons radiate coherently a broadband THz $ half cycle pulse whose average brightness is 45 orders of magnitude higher than synchrotron IR sources. Previous measurements showed 20 W of average power extracted [Carr, et al., Nature 420 (2002) 153]. The new facility offers simultaneous synchrotron light from the visible through the FIR along with broadband THz production of 100 fs pulses with 4200 W of average power.The FELs also provide record-breaking laser power [Neil, et al., Phys. Rev. Lett. 84 (2000) 662]: up to 10 kW of average power in the IR from 1 to 14 mm in 400 fs pulses at up to 74.85 MHz repetition rates and soon will produce similar pulses of 300-1000 nm light at up to 3 kW of average power from the UV FEL. These ultrashort pulses are ideal for maximizing the interaction with material surfaces. The optical beams are Gaussian with nearly perfect beam quality. See www.jlab.org/FEL for details of the operating characteristics; a wide variety of pulse train configurations are feasible from 10 ms long at high repetition rates to continuous operation.The THz and IR system has been commissioned. The UV system is to follow in 2005. The light is transported to user laboratories for basic and applied research. Additional lasers synchronized to the FEL are also available. Past activities have included production of carbon nanotubes, studies of vibrational relaxation of interstitial hydrogen in silicon, pulsed laser deposition and ablation, nitriding of metals, and energy flow in proteins. This paper will present the status of the system and discuss some of the discoveries we have made concerning the physics performance, design optimization, and operational limitations of such a first generation high power ERL light source. r

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Along with an ab initio recalculation of the NaHg(X1/2) ground state potential curve we present an identification of the chemiluminescence of the NaHg red bands. Based on quantum simulations of the relevant vibronic transitions following production of the NaHg molecule by the photochemical reaction via the sodium dimer, we propose the nascent population distribution in the upper NaHg(II1/2) state to peak at v′=2, described by a Gaussian distribution with α=0.023.

We report for the first time the production of the LiHg excimer by a photochemical reaction of excited Li2 molecules with Hg(6s 2 ISO)' Excitation energy was provided by a cw ultraviolet (UV)-argon ion laser operating in single-line and in multi-line mode or by pulsed XeCI excimer laser at 3080 A. We observed bound-free emission of LiHg in the form of diffuse bands peaking at 4450 and at 4670 A. The latter was structured by bound-bound emission lines. Relativistic ab initio calculations for the potential energy curves of LiHg and for the relevant dipole transition moments were performed. Using these results, an interpretation of the observed emission is presented.