Lessons learned and ongoing research at Electra: a rep-rate excimer laser facility

Electra is a repetitively pulsed, electron beam pumped excimer laser at the Naval Research Laboratory where we are developing the technologies that can meet the Inertial Fusion Energy (IFE) requirements for durability, efficiency, and cost. The technologies developed on Electra are designed to be directly scalable to a fusion power plant beam line. As in a full-size fusion power plant beam line, Electra has been utilized as the ultimate amplifier in a laser amplifier system. The 500 keV doubled sided electron beam pumped (100 ns flat-top) main amplifier in krypton fluoride (KrF) oscillator mode has demonstrated single shot and rep-rate laser energies exceeding 700 J with 100 ns pulse width at 248 nm with an aperture 29 x 29 cm². Continuous operation of the KrF electron beam pumped oscillator has lasted for more than 2.5 hours without failure at 1 Hz and 10 hours without failure at 2.5 Hz. The measured intensity and pulse energy for durations greater than thousand shots are consistent at measurable rep-rates of 1 Hz, and 2.5 Hz. The laser oscillator also demonstrated 50,000 shots on the same foils at 5 Hz operation. Recently, the electron beam diodes of the Electra facility have been modified to a reduced aperture to increase the power deposition rate for efficient argon fluoride at 193 nm operations. In addition, new electron beam window materials and configurations have been investigated to enhance ArF yield. The Electra facility achieved 200 Joules at 193 nm with single shot performance with a reduced (relative to KrF) lasing beam size of 10 x 29 cm². Gain measurements at 193 nm indicate higher wall-plug efficiency for ArF (10%) than KrF (7%). The native emission of argon fluoride bandwidth exceeds 10 THz which is broader than the krypton fluoride bandwidth of a few THz.