3D printing technology creates objects by adding molten plastic or metal layers, but this technique is limited to larger sizes. Scientists have questioned how to manufacture microdevices that cannot be produced using layering and whether it is conceivable to directly print inside a pre-existing three-dimensional material.
The teams led by Lynford Goddard and Paul Braun, both faculty members at the University of Illinois Urbana-Champaign, have been working together to create a procedure for this purpose. They utilized multiphoton lithography to imprint within a pre-existing permeable substance by applying a laser beam with high intensity.
The scientists were able to alter specific areas of the inside and create personalized miniature optical gadgets using a technique known as subsurface controllable refractive index via beam exposure (SCRIBE).
Both teams of researchers have revealed an enhancement to this process, enabling them to have greater precision over the final products. ACS Photonics has recently released the details of this new procedure.
We were able to show an improvement from a baseline of 36% to a new value of 49% in the efficiency of fabricated lenses and a clear improvement in the color uniformity resulting from the 2D line gratings we made. We believe that this new technique will open the door to a vast array of optical element designs.
Alexander Littlefield, Study Lead Author and Graduate Student, University of Illinois Urbana-Champaign
The process known as SCRIBE utilizes two-photon absorption as a mechanism for multiphoton lithography. According to scientists, transparent silica is created by oxidizing silicon that has been etched to contain tiny pores at a microscopic level.
Afterward, they stuff it with a substance known as photoresist, which can experience a chemical reaction that alters its optical characteristics solely upon absorption of two photons simultaneously. This phenomenon is infrequent unless extremely strong light is utilized.
Scientists use this technique by concentrating laser beams to generate high magnitudes in distinct areas. This enables them to produce personalized blueprints for the optical features of the substance in three dimensions to “write” optical constituents.
Earlier versions of SCRIBE were constrained by inadequate management of the laser's strength. To tackle this, the researchers propose three enhancements to the method in their study. Initially, they utilize a two-photon fluorescence imaging mechanism to chart the density of the photoresist and adjust the laser potency necessary for the intended outcome.
They also rectify discrepancies that are particularly noticeable close to the writing perimeter by adjusting the substance's placement during laser inscription. Ultimately, they incorporate a temporal gap between laser bursts to reduce time-related impacts on the photoresist interaction.
By integrating these three enhancements, the scientists attained greater command over their patterned apparatus, resulting in more accurately produced constituents that exhibit higher efficiency.
To showcase the adaptability of their technique, they produced a 100-by-100-micrometer optical mechanism that modifies light to create definite chromatic designs, a linear diffraction grating that duplicates the configuration and hues of the UIUC emblem.
Our work shows that multiphoton lithography can now accurately fabricate microscale optical components with new capabilities that do not yet exist for other fabrication methods.
Lynford Goddard, Professor, Electrical and Computer Engineering, University of Illinois Urbana-Champaign
Goddard works as a faculty member in electrical and computer engineering, while Braun is employed as a faculty member in materials science and engineering.
Littlefield, along with graduate students Lawrence Ju, Jingxing Gao, and Lonna Edwards from Goddard’s team, and Dajie Xie, Corey Richards, and Christian Ocier from Braun’s team, as well as undergraduate students Haibo Gao and Jonah Messinger, all made contributions to this study.
The research staff at the UIUC and the University of Illinois Chicago assisted with the experiments, including but not limited to Jeff Grau, Austin Cyphersmith, Anuj Singhal, and Seyoung An.
The study was partially funded by The Grainger College of Engineering at UIUC, the National Science Foundation, and the Department of Energy. This work received additional assistance through fellowships granted by the Department of Defense and UIUC.
Littlefield, A. J., et al. (2023) Enabling High Precision Gradient Index Control in Subsurface Multiphoton Lithography. ACS Photonics. doi:10.1021/acsphotonics.2c01950.