Generating Low-Temperature Layers with Infrared Heating

Cryogenic targets for the National Ignition Facility require uniform solid layers inside spherical capsules at temperatures ~1.5 K below the triple point of hydrogen. Uniform layers have been successfully formed near the triple point. However, upon subsequent cooling the layers degrade. We report here recent attempts to form uniform deuterium hydride (HD) layers 1.5 K below the triple point using infrared (IR) radiation. Pumping the IR collisionally induced vibration-rotation band of solid HD contained inside a transparent plastic shell generates a volumetric heat source in the HD lattice. This in turn allows the formation of a spherical crystalline shell of HD inside the transparent plastic shell. HD layers ~50 m thick have been formed near the triple point and slowly cooled 1.5 K under high IR power without layer degradation.