LLNL Researchers Develop New Method of 3D Printing Transparent Glass for Optical Applications

The 3D printing of glass has been in the news quite a lot lately, with several breakthroughs coming in the last couple of months. Micron3DP is releasing its glass 3D printer after installing several units at its own factory, and researchers from the Karlsruhe Institute of Technology (KIT) recently developed a method of 3D printing glass on an SLA printer. Now scientists at Lawrence Livermore National Laboratory (LLNL) have come up with a new way of 3D printing transparent glass for applications involving optics.

Wait, you might say, isn’t all glass transparent? Not entirely, especially when it’s 3D printed. The most common methods of 3D printing glass involve the extrusion of molten glass filament or the sintering of glass powders, and they tend to result in porous or non-uniform structures that aren’t clear enough for optical applications such as lasers. Lawrence Livermore took a different approach, creating an ink from concentrated suspensions of silica particles with highly controlled flow properties that can be 3D printed at room temperature.

Once the structures are 3D printed, using a direct ink writing process, they are put through a specialized thermal treatment to make them denser and remove print lines. They are then given an optical quality polish.

“For printing high-quality optics, you shouldn’t be able to see any pores and lines, they have to be transparent,” said LLNL materials engineer Du Nguyen. “Once we got a general formulation to work, we were able to tweak it so the material could merge during the printing process. Most other groups that have printed glass melt the glass first and cool it down later, which has the potential for residual stress and cracking. Because we print at room temperature, that’s less of an issue.”

The process could allow for the 3D printing of glass that incorporates different refractive indices in a single flat optic, as opposed to the special shapes that are required for those refractive characteristics to be achieved in constant composition glass. That means lenses that are easier and cheaper to fabricate.

“Polishing complex or aspheric lenses is pretty labor-intensive and requires a lot of skill, but polishing a flat surface is much easier,” Nguyen said. “By controlling the refractive index in the printed parts, you alter the bending of light, which enables a lens that could be polished flat.”

The researchers aren’t necessarily looking to replace traditional optics, but rather to develop new applications with composition gradients that don’t currently exist on the market. Designing new optical components instead of using what’s already available could result in the reduction of size, weight and cost.

“Optical fabrication research and development is trending toward freeform optics, which are optics that can be made virtually to any complex shape,” said Tayyab Suratwala, LLNL’s program director for Optics and Material Science and Technology. “Expanding this to 3D-printed optics with compositional variation can greatly increase the capabilities of this new frontier.”

The technology could also have applications outside of optics – for example, in microfluidics. Glass is a favored material in microfluidics, thanks to its transparency, chemical resistance, mechanical properties and customization potential in terms of surface chemistry and functionality. However, it’s difficult to machine and etch complex microfluidic devices from glass, which makes 3D printing highly appealing for the field.

“Achieving compositional and structural control for functional materials, in this case for optical components and microfluidics, promises to tremendously open up the application space for 3D-printing technologies,” said materials engineer Eric Duoss. “It’s not easy to do, however our multidisciplinary team was able to identify and overcome challenges in a broad range of areas including chemistry, materials, engineering, physics and optics, to create a robust and repeatable approach to printing glass.”

The next step is the actual creation of high-quality optics and gradient index lenses, made by varying the composition of the glass. More research will be required to achieve Gradient Refractive Index (GRIN) optics.

“The Lab is always looking for different ways to create new materials for optical applications,” said LLNL chemical engineer and project lead Rebecca Dylla-Spears. “We’re not going to replace the optical materials made through traditional means, but we’re trying to impart new functionality using additive manufacturing. This is the first step to being able to print compositionally graded glass optics.”

The research was published in a paper entitled “3D-Printed Transparent Glass,” which you can access here. Authors include Du T. Nguyen, Cameron Meyers, Timothy D. Yee, Nikola A. Dudukovic, Joel F. Destino, Cheng Zhu, Eric B. Duoss, Theodore F. Baumann, Tayyab Suratawala, James E. Smay, and Rebecca Dylla-Spears. Discuss in the LLNL forum at 3DPB.com.

[Source/Images: LLNL]