Full System Operations of Mercury; A Diode-Pumped Solid-State Laser

Operation of the Mercury laser with two amplifiers activated has yielded 30 Joules at 1 Hz and 12 Joules at 10 Hz and over 8 x 10{sup 4} shots on the system. Static distortions in the Yb:S-FAP amplifiers were corrected by magneto rheological finishing technique

The Mercury Project: A High Average Power, Gas-Cooled Laser For Inertial Fusion Energy Development

Hundred-joule, kilowatt-class lasers based on diode-pumped solid-state technologies, are being developed worldwide for laser-plasma interactions and as prototypes for fusion energy drivers. The goal of the Mercury Laser Project is to develop key technologies within an architectural framework that demonstrates basic building blocks for scaling to larger multi-kilojoule systems for inertial fusion energy (IFE) applications. Mercury has requirements that include: scalability to IFE beamlines, 10 Hz repetition rate, high efficiency, and 10{sup 9} shot reliability. The Mercury laser has operated continuously for several hours at 55 J and 10 Hz with fourteen 4 x 6 cm{sup 2} ytterbium doped strontium fluoroapatite (Yb:S-FAP) amplifier slabs pumped by eight 100 kW diode arrays. The 1047 nm fundamental wavelength was converted to 523 nm at 160 W average power with 73% conversion efficiency using yttrium calcium oxy-borate (YCOB)

Analysis of Sr5xBax(J?04)3FYb* crystals for improved laser performance with diode-pumping This paper was prepared for submittal to the 12th Topical Meeting on Advanced Solid-State Lasers Analysis of Sr$xBax(P04)3F: Yb3+ crystals for improved laser perform

Abstract Crystals of Yb3+:Sr,.XB~(P0,)jF (O < x < 5) have been investigated as a means to obtain broader absorption bands than are currently available with Yb3+:S-FAP [Yb3+:Sr~(P0,)~F], thereby improving diode-pumping eftlciency for high peak power applications. Large diode-arrays have a FWHM pump band of 25 nm while the FWHM of the 900 nm absorption band for Yb:S-FAP is 5.5 nm; therefore, a significant amount of pump power can be wasted due to the nonideal overlap. Spectroscopic analysis of Yb:Sr~.XB~-FAP crystals indicates that adding barium to the lattice increases the pump band to 13-16 nm which more than compensates for the diodearray pump source without a detrimental reduction in absorption cross section. However, the emission cross section decreases by approximately half with relatively no effect on the emission lifetime. The small signal gain has also been measured and compared to the parent material Yb:S-FAP and emission cross sections have been determined by the method of reciprocity, the FUchtbauer-Ladenburg method, and small signal gain. Overall, Yb3+:Sr,. ,B~(PO,)JF crystals appear to achieve the goal of nearly matching the favorable thermal and laser performance properties of Yb:S-FAP while having a broader absorption band to better accommodate diode pumping

Upconversion-pumped luminescence efficiency of rare-earth-doped hosts sensitized with trivalent ytterbium

We discuss the upconversion luminescence efficiencies of phosphors that generate red, green, and blue light. The phosphors studied are single crystals and powders co-doped with Er{sup 3+} and Yb{sup 3+}, and with Tm{sup 3+} and Yb{sup 3+}. The Yb ions are pumped near 980 nm; transfers of two or three quanta to the co-doped rare earth ion generate visible luminescence. The main contribution embodied in this work is the quantitative measurement of this upconversion efficiency, based on the use of a calibrated integrating sphere, determination of the fraction of pump light absorbed, and careful control of the pump laser beam profile. The green phosphors are the most efficient, yielding efficiency values as high as 4 %, with the red and blue materials giving 1 - 2 %. Saturation was observed in all cases, suggesting that populations of upconversion steps of the ions are maximized at higher power. Quasi-CW modeling of the intensity- dependent upconversion efficiency was attempted; input data included level lifetimes, transition cross sections, and cross-relaxation rate coefficients. The saturation of the Yb,Er:fluoride media is explained as the pumping of Er{sup 3+} ions into a bottleneck (long-lived state)- the {sup 4}I{sub 13/2} metastable level, making them unavailable for further excitation transfer. 32 refs., 5 figs., 3 tabs

The mercury laser system – An average power, gas-cooled, Yb:S-FAP based system with frequency conversion and wavefront correction

We report on the operation of the Mercury laser with fourteen 4 $\times$ 6 cm$^{2}$ Yb:S-FAP amplifier slabs pumped by eight 100 kW peak power diode arrays. The system was continuously run at 55 J and 10 Hz for several hours, (2$\times$10$^{5}$ cumulative shots) with over 80% of the energy in a 6 times diffraction limited spot at 1.047 $\mu$m. Improved optical quality was achieved in Yb:S-FAP amplifiers with magneto-rheological finishing, a deterministic polishing method. In addition, average power frequency conversion employing YCOB was demonstrated at 50% conversion efficiency or 22.6 J at 10 Hz

Demonstration of ignition radiation temperatures in indirect-drive inertial confinement fusion hohlraums

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of TRAD=300  eV and a symmetric implosion to a 100  μm diameter hot core