There are many scientific and engineering applications of transparent glass including optics, communications, electronics, and hermetic seals. However, there has been minimal research toward the additive manufacturing (AM) of transparent glass parts. This paper describes and demonstrates a filament-fed technique for AM of transparent glass. A transparent glass filament is melted by a CO2 laser and solidifies as the workpiece is translated relative to the stationary laser beam. To prevent thermal shock, the workpiece rests on a heated build platform. In order to obtain optically transparent parts, several challenges must be overcome, notably producing index homogeneity and avoiding bubble formation. The effects of key process parameters on the morphology and transparency of the printed glass are explored experimentally. These results are compared to a low-order model relating the process parameters to the temperature of the molten region, which is critical to the quality of the deposited glass. At lower temperatures, the glass is not fully melted, resulting in index variations in the final part, while at higher temperatures, phase separation introduces bubbles and other defects into the part. The correct process avoids these issues and deposits optically transparent glass.

A time efficient and costless lift-off process combined with the anodic bonding method was used to create a ‘shale-like’ glass–silicon–glass microfluidic model.

Microsphere photolithography (MPL) is a practical, cost-effective nanofabrication technique. It uses self-assembled microspheres in contact with the photoresist as microlenses. The microspheres focus incident light to a sub-diffraction limited array of photonic jets in the photoresist. This Letter explores the MPL technique to pattern metal-insulator-metal metasurfaces with near-perfect absorption at mid-wave infrared (MWIR) frequencies. Experimental results are compared to electromagnetic simulations of both the exposure process and the metasurface response. The microsphere self-assembly technique results in a polycrystalline metasurface; however, the metal-insulator-metal structure is shown to be defect tolerant. While the MPL approach imposes geometric constraints on the metasurface design, once understood, the technique can be used to create functional devices. In particular, the ability to tune the resonant wavelength with the exposure dose raises the potential of hierarchical structures.

Fabricating metasurfaces over large areas at low costs remains a critical challenge to their practical implementation. This paper reports on the use of microsphere photolithography (MPL) to create infrared metasurfaces by changing the angle-of-incidence of the illumination to steer the photonic jet. The displacement of the photonic jet is shown to scale with the diameter of the microsphere while the exposure dose scales with the square of the microsphere diameter. This process is robust in the presence of local defects in the microsphere lattice. The paper demonstrates patterning split ring resonators and tripole based metasurfaces using MPL, which are fabricated and characterized with FTIR. The combination of bottom-up and top-down approaches in off-normal incidence microsphere photolithography technique provides cost-effective, flexible, and high-throughput fabrication of infrared metasurfaces.

Using an enriched pre-chamber is an effective way to extend the lean limit, to reduce the nitrogen oxide emissions and to avoid abnormal combustion in spark ignition natural-gas engines. Enrichment injection in the pre-chamber of a spark ignition natural-gas engine determines the flow field and the fuel–air mixture formation quality in the pre-chamber and has a profound influence on the combustion performance of the engine. In order to study the characteristics of enrichment injection in the pre-chamber of a natural-gas engine, two-dimensional particle image velocimetry measurements and three-dimensional computational fluid dynamics calculations were carried out. The influence of the enrichment injection angle on the engine performance was investigated with the aid of a computational fluid dynamics simulation tool. The results indicate that a change in the enrichment injection angle directly affects the gas motion, the fuel–air mixture formation, the flame propagation and the formation of nitrogen oxides in the pre-chamber and further influences the penetration of the flame jets, the combustion temperature distribution and the formation of nitrogen oxides in the main chamber. There is an optimal injection angle for this research engine. Of the four injection angles that were investigated, an injection angle of 14° results in the lowest nitrogen oxide emissions.