An official website of the United States government
Two-photon polymerization (TPP) is an advanced 3D fabrication technique capable of creating features with submicron precision. A primary challenge in TPP lies in the facile and accurate characterization of fabrication quality, particularly for structures possessing complex internal features. In this study, we introduce an automated brightfield layerwise evaluation technique that enables a simple-to-implement approach forin situmonitoring and quality assessment of TPP-fabricated structures. Our approach relies on sequentially acquired brightfield images during the TPP writing process and using background subtraction and image processing to extract layered spatial features. We experimentally validate our method by printing a fibrous tissue scaffold and successfully achieve an overall system-adjusted fidelity of 87.5%in situ. Our method is readily adaptable in most TPP systems and can potentially facilitate high-quality TPP manufacturing of sophisticated microstructures.
more »
« less
Generic fabrication solution of freeform Fresnel optics using ultra-precision turning
Freeform Fresnel optics represent an emerging category of modern optics that reproduces powerful optical functionalities while maintaining an ultra-compact volume. The existing ultra-precision machining (UPM) technique faces technical challenges in meeting the fabrication requirements for freeform Fresnel optics because of the absence of appropriate geometry definition and corresponding tool path planning strategy to overcome the extreme asymmetry and discontinuity. This study proposes a new scheme for ultra-precision machining using four axes (X,Y,Z,C) to fabricate freeform Fresnel optics, including a general geometry description for freeform Fresnel optics, the quasi-spiral tool path generation strategy to overcome the lack of rotary symmetry, and the adaptive tool pose manipulation method for avoiding tool interference. In addition, the tool edge compensation and the adaptive timestep determination are also introduced to enhance the performance and efficiency of the proposed scheme. The machining of two exemplary freeform Fresnel lenses is successfully demonstrated. Overall, this study introduces a comprehensive routine for the fabrication of freeform Fresnel optics and proposes the adaptive tool pose manipulation scheme, which has the potential for broader applications in the ultra-precision machining of complex or discontinuous surfaces.
more »
« less
- Award ID(s):
- 2229170
- PAR ID:
- 10544523
- Publisher / Repository:
- Optica
- Date Published:
- Journal Name:
- Optics Express
- Volume:
- 31
- Issue:
- 26
- ISSN:
- 1094-4087
- Page Range / eLocation ID:
- 44622
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Freeform optics can reduce the cost, weight, and size of advanced imaging systems, but it is challenging to manufacture the complex rotationally asymmetric surfaces to optical tolerances. To address the need for disruptive, high-precision sub-aperture forming and finishing techniques for freeform optics, we investigate an alternative, non-contact polishing methodology using femtosecond lasers, combining modeling, experiments, and demonstrations. Femtosecondlaser- based polishing of germanium was investigated using an experimentally-validated twotemperature model of laser/germanium interaction to guide the understanding and selection of laser parameters to achieve near-nonthermal ablation for polishing and figuring. For the first time to our knowledge, model-guided femtosecond laser polishing of germanium was successfully demonstrated, achieving precision material removal while maintaining single-digit nanometer optical surface quality. The demonstrated femtosecond-laser-based polishing technique lays the foundation for semiconductor optics polishing/fabrication using femtosecond lasers and opens a viable path for high-precision, complex sub-aperture optical polishing tasks on various materials. © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreementmore » « less
-
Plastics offer innumerable societal benefits but simultaneously contribute to persistent environmental pollution, dominated by polyethylene (PE) and isotactic polypropylene (iPP). Melt blending and reformulating postconsumer PE andiPP into useful materials presents a promising recycling approach. However, such repurposed plastics are generally mechanically inferior due to an inability to efficiently separate polyolefins in mixed waste streams; phase separation of PE andiPP results in brittleness as a consequence of poor interfacial strength. Recently, we demonstrated that a small amount (1 wt%) of a poly(ethylene)-block-poly(ethyl ethylene-ran-ethylene)-block-poly(ethylene) (EXE) triblock copolymer, synthesized by low-cost anionic polymerization of 1,3-butadiene followed by solution hydrogenation, restores tensile toughness to levels equivalent to virgin polyolefins. Unfortunately, low-temperature solvent insolubility of EXE, driven by crystallization of the E blocks containing 1.5 ethyl branches per 100 backbone repeat units (EB), presents a challenge for industrial hydrogenation. Comparable toughness (ca. > 400% strain at break) was achieved in the present work with 1.5 ≤ EB ≤ 6.5, accompanied by reduced EXE crystallinity and dissolution in cyclohexane down to room temperature at the highest EB content. This remarkable toughening behavior is attributed to a synergy between chain entanglements between the E end blocks and semicrystalline PE homopolymer and formation of E block “crystal nodules” that prevent chain pullout, along with topological constraints between the X loops and semicrystallineiPP. Our findings overcome barriers to commercial production of EXE with existing industrial facilities, providing a cost-effective strategy for recycling PE andiPP.more » « less
-
Hockett, Kevin Loren (Ed.)ABSTRACT Rhizopus microsporusis a necrotrophic post-harvest pathogen that causes significant economic losses in the agricultural sector. To explore alternatives to conventional management strategies for the mitigation of post-harvest infections, we investigated the potential of two previously identified endophyticBacillus velezensisstrains as biological control agents. Throughin vitroandin vivoexperiments, we examined the mechanisms of biocontrol displayed by twoB. velezensisstrains (KV10 and KV15) against threeR. microsporusstrains (W2-50, W2-51, and W2-58).In vitroassays assessed co-cultivability and the inhibitory effects ofB. velezensisagainstR. microsporus. The results demonstrated strain-specific antifungal activity with a reduction in fungal growth across treatments. Further analysis revealed that volatile organic compounds produced byB. velezensiscontributed to its antifungal properties. To evaluate the biocontrol efficacyin vivo, tomato fruits were inoculated withR. microsporusand subsequently treated withB. velezensis. The results support the strain-specific reduction in tomato spoilage, yielding various spoilage rates observed across treatments. Our findings highlight the potential ofB. velezensisas a promising biocontrol agent for the management ofR. microsporuspost-harvest infections in tomatoes. Further research is warranted to optimize the applicationof B. velezensisas a sustainable and environmentally friendly approach for controlling post-harvest diseases in tomatoes.IMPORTANCEOur study shows the significance of improving sustainable agriculture by offering an alternative to the use of chemical fungicides in post-harvest applications. Opportunistic fungal pathogens likeRhizopus microsporuscan have detrimental effects on post-harvest commodities like tomatoes. Post-harvest fungal infections are mainly controlled by chemical fungicides that pose health risks to humans and the environment. Utilizing biocontrol agents provides an environmentally safe alternative. Understanding the mechanisms of biocontrol employed by beneficial bacteria likeBacillus velezensison fungal pathogens gives insight into safer, more environmentally friendly alternatives to protect food crops. Our results suggest that targeted microbial solutions can mitigate post-harvest losses.more » « less
-
This paper presents a study of the grinding of three different grades of silicon carbide (SiC) under the same conditions. Surface topography is analyzed using coherent scanning interferometry and scanning electron microscopy. The study provides a baseline understanding of the process mechanics and targets effective selection of process parameters for grinding SiC optics with near optical level surface roughness, thus reducing the need for post-polishing. Samples are raster and spiral ground on conventional precision machines with metal and copper-resin bonded wheels under rough, medium, and finish grinding conditions. Material microstructure and grinding conditions affect attainable surface roughness. Local surface roughness of less than 3 nm RMS was attained in both chemical vapor deposition (CVD) and chemical vapor composite (CVC) SiC. The tool footprint is suitable for sub-aperture machining of a large freeform optics possibly without the need for surface finish correction by post-polishing. Subsurface damage will be assessed in Part 2 of this paper series.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1364/OE.509238
