In the framework of THRILL’s work package 4 “High-repetition-rate high-energy amplification”, Amplitude developed and prototyped a novel flashlamp-pumped Nd:Glass slab amplifier named PAMDAM (Pseudo Active Mirror Disk Amplifier Module) with a large diameter of 170mm, paving the way toward high-rep rate kJ beam. Its liquid-cooled slab design enables a strong thermal extraction and operation up to 1shot/min, order of magnitude faster than passive Nd:Glass amplifiers in use in current Inertial Fusion facilities. As the laser beam is crossing the cooling fluid, the fluid properties and flow homogeneity are critical. Amplitude tested various exotic fluids, some of them never used in laser industry. Amplitude validated a patented smoothing flow injection device, removing any refractive-index riddles, enabling beam propagation over 10s of meters while keeping spatial homogeneity. Thermalization occurs in 10min, showing the efficiency of the cooling.
Flashlamps-pumped design is a very cost-effective and durable way to pump the Nd-doped Glass, but the large angular emittance of lamps leads to a poor coupling in conventional Brewster slab geometry. Here the Pseudo-active mirror enables to maximize the coupling between the lamp and the laser glass, and to maximize the stored energy extraction. We explored new coupling geometries and demonstrated a stored energy of 300J, leading to a laser energy available for extraction of 150J per PAMDAM at 1shot per minute. Such amplifiers bring high-rep rate kJ-class lasers with temporal shaping closer to an off-the-shelf solution, while the cost-effectiveness of flashlamps keep such a laser relevant for research institutes. Future developments should be carried out regarding the chemical resistance of the cooling fluid and its interaction with laser materials. Our results show as well the importance of mitigating transverse lasing to rise the stored energy. New research on cladding and glass adhesion could open a path for more versatile slabs geometry, and major innovations in amplifier design.
The PAMDAM Characterization Plan is available for download as D4.2.
Image: Left: Front view of the external dichroic mirror and the PAMDAM inside its gimbal mount; Right: Schematic of the 200mm PAMDAM with two cooling fluids circuits, one for the flash lamps and one for the optical assembly, separated by a window. Dichroic mirrors enable the transmission and reflection of the incoming IR beam and the transmission of the lamps white light.
