Diode-pumped solid state laser driver experiments for inertial fusion energy a

摘要

Abstract: Although solid-state lasers have been the primary means by which the physics of inertial confinement fusion (ICF) have been investigated, it was previously thought that solid-state laser technology could not offer adequate efficiencies for an inertial fusion energy (IFE) power plant. Orth and co-workers have recently designed a conceptual IFE power plant, however, with a high efficiency diode-pumped solid-state laser (DPSSL) driver that utilized several recent innovations in laser technology. It was concluded that DPSSLs could offer adequate performance for IFE with reasonable assumptions. This system was based on a novel diode pumped Yb-doped Sr$-5$/(PO$-4$/)$-3$/F(Yb:S-FAP) amplifier. Because this is a relatively new gain medium, a project was established to experimentally validate the diode-pumping and extraction dynamics of this system at the smallest reasonable scale. This paper reports on the initial experimental results of this study. We found the pumping dynamics and extraction cross-sections of Yb:S-FAP crystals to be similar to those previously inferred by purely spectroscopic techniques. The saturation fluence for pumping was measured to be 2.2 J/cm$+2$/ using three different methods based on either the spatial, temporal, or energy transmission properties of a Yb:S-FAP rod. The small signal gain implies an emission cross section of 6.0 multiplied by 10$+$MIN@20$/ cm$+2$/ that falls within error bars of the previously reported value of 7.3 multiplied by 10$+$MIN@20$/ cm$+2$/, obtained from spectroscopic techniques. Up to 1.7 J/cm$+3$/ of stored energy density was achieved in a 6 multiplied by 6 multiplied by 44 mm$+3$/ Yb:S-FAP amplifier rod. In a free running configuration diode-pumped slope efficiencies up to 43% were observed with output energies up to approximately 0.5 J per 1 ms pulse from a 3 multiplied by 3 multiplied by 30 mm$+3$/ rod. When the rod was mounted in a copper block for cooling, 13 W of average power was produced with power supply limited operation at 70 Hz with 500 microsecond pulses. !9