This PDF file contains the front matter associated with SPIE Proceedings Volume 11168 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Ultrashort ring-Airy laser beams with tunable characteristics are experimentally generated and employed for the advanced fabrication of large 3D structures with high resolution using multiphoton polymerization. These beams can be adjusted to abruptly autofocus over an extended range of working distances while keeping almost invariant their voxel shape and dimensions. This striking property together with the real-time controlled focus tuning, through a spatial light modulator, make them ideal candidates for long range multiphoton polymerization. Moreover, the paraxial ring-Airy beams can approach the wavelength limit when scaling down, while observing a counterintuitive, strong enhancement of their focal peak intensity. Using numerical simulations, we show that this behavior is a result of the coherent constructive action of paraxial and nonparaxial energy flow.

This paper summarizes our work on DNA-based nanofabrication. In the past decade, our group has developed several strategies to employ unmodified DNA nanostructures as templates for high-resolution patterning. We showed that DNA nanostructures can locally modulate vapor phase etching and deposition reactions. As a result, both negative-tone and positive-tone pattern transfers were achieved within one reaction system by adjusting reaction conditions. We also showed that DNA nanostructures can be directly imprinted onto a variety of substrates, including soft polymers and selfassembled monolayer molecules. In these cases, various surface patterns were obtained with the size ranging from micrometer to sub-10 nm. These DNA-patterned substrates have interesting interfacial properties, such as site-specific reactivity and antifouling. Overall, our work highlighted the potentials of DNA-based nanofabrication for high-resolution patterning in electronic and surface engineering applications.

Our previously developed plasma chemical vaporization machining (CVM) does not apply a load to the surface to be figured during its process. Thus, plasma CVM is expected to be able to process lightweight mirrors having a surface with thin parts supported by ribs with high accuracy. In this study, we investigated the removal characteristics of plasma CVM for fused silica workpieces having thin and thick parts simulating a lightweight mirror. The experimental results showed that such workpieces were processed with a uniform removal depth by placing a fused silica column at the back of the thin part. Moreover, a flat surface having a thin part of 0.6 mm thickness was figured by plasma CVM, where a column was placed in the thin part in the same way as in the fundamental study. As a result, we successfully demonstrated that plasma CVM enables the figuring of an optical surface with thin parts.

The particular properties of hollow whispering gallery resonators should lead to the advancement of bio- and chemical sensing applications. In this talk, we report on the fabrication of, and mode propagation in, hollow, thin-walled microcavities, known as microbubbles or microbottles, which are made from microcapillaries that are pretapered, then heated using a CO2 laser while flowing air through them. The resulting cavity consists of a thin glass shell supported on a hollow stem through which fluid can flow. Whispering gallery modes supported in the wall of the cavity create an evanescent field extending from both the inner and outer surfaces. For higher order modes, and playing with material refractive indices, the system can be engineered so that most of the optical energy extends into the contained fluid, thereby allowing for strong interactions to be present; such a cavity is called a quasi-droplet. Even tiny changes to the fluid, such as the presence of nanoparticles, can lead to a significant shift of the resonance frequencies of the whispering gallery modes. These strongly interacting quasi-droplets make hollow microresonators uniquely suited for sensing applications.

Close related to the strong evolution of the Internet of Things (IoT) and Industry 4.0 concepts, enabling new services and production paradigms, smart and multifunctional materials are a key driving force for the development of wireless, sustainable and interconnected systems. Thus, printed smart materials is an area of increasing interest due to low-cost fabrication, simple integration into devices and possibility of obtaining multifunctional materials over large and flexible areas. The impact of printable smart and multifunctional materials span from the areas of sensors and actuators, to energy generation and storage and tissue engineering applications, among others. The present talk will summarize the main features, achievements and the challenges associated with various printing technologies. Further, the most relevant smart materials that are already being printed, mainly piezoelectric, piezoresistive, magnetostrictive and shape memory polymers will be discussed together with some of the most representative applications. Finally, critical challenges and future research directions will be indicated.

Although electrospinning is well-known to produce non-woven nanofibrous mats under the action of a high electric field, it is shown that by using synergistically the processes of electrospinning and electrospraying, it is possible to build well controlled 2D and even 3D micro-patterned composites. The building of such nanofibrous constructs is governed by the electric charge distribution accumulated at the surface of the material during the alternate deposition of electrospun nanofibers and electrosprayed microparticles thanks to an “electrostatic template assisted deposition” (ETAD).[1] Experimental investigations allowed the estimation of the amount of charges of the single electrospun jet as a function of the processing conditions. Furthermore, in the case of two simple collectors, i.e. a flat cylinder or a cylinder with grooves of adjustable width, the measurement of the voltage at the surface of the deposited fibers during electrospinning gave more insight into the local charges distribution as well as the kinetic of the charges release. These results allowed a deep understanding of the building of an “electrostatic template” over the electrospun fibers leading to precisely control the trajectory of the microparticles during the electrospraying step. The role of the properties (conductivity and amount of residual solvent) of the microparticles on the quality of the “electrostatic template” and thus on the control of the formation of patterned 2D and 3D nanofibrous composites was also investigated. In order to apply the concept of ETAD process, several micropatterned substrates with different kinds of structures in height and characteristic lateral sizes ranging from few tens to few hundreds of microns were used as collectors. Then, electrospun fibers and electrosprayed microparticles were alternately deposited onto these collectors fixed on a rotary drum. Microstructured 2D bi-layer composites were obtained after an electrospinning step followed by an electrospraying step. Numerical simulations of this two-steps process were conducted[2] and gave more insight into the mechanism of deposition. When electrospinning and electrospraying are carried out alternately, the electrostatic template effect is kept during the deposition steps and a 3D microstructured composite is obtained. Depending on the nature of the nanofibers and the microparticles, such 2D and 3D micropatterned materials can find applications in different fields such as biochips[1], biomimetic scaffolds[3] or sensor applications. References: [1] S. Nedjari, A. Hébraud, S. Eap, S. Siegwald, C. Mélart, N. Benkirane-Jessel, G. Schlatter, "Electrostatic Template-Assisted Deposition of Microparticles on Electrospun Nanofibers: Towards Microstructured Functional Biochips for Screening Applications", RSC Advances, vol. 5, pp. 83600-83607, 2015. [2] Corinne R. Wittmer, Anne Hébraud, Salima Nedjari, Guy Schlatter, "Well-Organized 3D Nanofibrous Composite Constructs using Cooperative Effects between Electrospinning and Electrospraying", Polymer, vol. 55, pp. 5781-5787, 2014. [3] A. Garcia Garcia, A. Hébraud, J-L. Duval, L. Gaut , C. Wittmer, D. Duprez, C. Egles, F. Bedoui, G. Schlatter, C. Legallais, "Poly(-caprolactone)/hydroxyapatite 3D honeycomb scaffolds for a cellular microenvironment adapted to maxillofacial-bone reconstruction", ACS Biomaterials Science and Engineering, vol. 4, pp. 3317–3326, 2018.

The importance of additive manufacturing for optical components and systems is steadily increasing. Conventional 3D printing processes such as multi-jet modeling or stereo lithography were initially used to realize passive optical components. The advantage is that with the help of additive manufacturing optical components can be realized with a complex structure. The challenge is thereby the surface quality of the components produced. Due to the process-related layer structure, steps occur on curved surfaces. Another disadvantage of the layer structure is that it acts on the one hand like a diffraction grating and on the other hand, it contributes to the volume scattering of the light. These disadvantages are attempted to be compensated by adapted printing or post-processing methods. Irrespective of this, the 3D printing of passive optical components has a wide variety of application fields, especially in the field of illumination. The next step in the additive manufacturing of optical components is now to achieve a higher functionalization of the components, thus turning form passive to active optics, meaning that besides shaping of light rays the component can emit light on its own. Specifically, this means that the printed materials are mixed with other materials to allow additional light emission. In this talk, the potential of additive manufacturing of passive optical components is introduced by examples. The main part of the talk then focuses on the active 3D printed optical components. For this purpose, we present two different concepts. On the one hand, the integration of optically active quantum dots (for example, CdSe / ZnS nanoparticles) in 3D printing materials. These nanoparticles emit a defined wavelength when excited by UV light. It would be desirable now that not only quantum dots of a certain size / type are printed in an optical component, but also that locally a material mix of different quantum dots can be realized. Thus, a single optical component can emit spatially resolved different wavelengths. In order to do so, we rebuilt a standard stereolithography printer so that we can use different materials in x, y plane and z direction. In this way, we realized an optically active analysis chip for biological samples. The second concept is 3D printing of a random laser. For this purpose, we mixed nanoparticles (Nd-YAG particles) and Rhodamin as an active material into the 3Dprinting polymer. We show different forms of optically active components printed with this material. In order to prove the effect of random lasing, we pumped the samples with pulsed laser light (10Hz Nd-YAG laser, 532nm) and measured the emitted laser radiation. Finally, we give a brief presentation of the development of an additive manufacturing platform based on robots. The aim of the platform is to enable additive manufacturing with 6 degrees of freedom. In the development of the platform, we take the requirements for printing of optical components into account.

Free-form microoptics is a promising field showing immense potential in providing functional tools for light control, imaging and material processing. At the moment there is a huge drive in merging these objects to mesoscale – ensuring nano-/micro-features yet being mm-cm in overall size. One of the promising technologies to produce such elements is 3D laser lithography (3DLL). It has been shown to be a superb for fabrication of 3D objects with resolution and surface roughness control down to nm level with overall size to cm range [1]. For this reason it was employed to manufacture integrated 3D optical elements on functional substrates for spatial light control [2], imaging [3] and material processing [4]. Despite current progress there is some limitations concerning mesooptical element 3D printing. Common 3DLL systems uses galvo-scanners for beam deflection. While it can be very rapid (translation velocity in cm/s range), only objects that do not exceed working field of an objective can be printed continuously, which is ~100 µm for objectives having NA>1. Segment-by-segment fabrication have to be employed for bigger objects. At every edge where two segments meet, this induces defects called “stitches”. In optical element, it forces to sacrifice their quality [5] or use alternative manufacturing techniques [6]. In this work we present a stitch-free 3D printing of functional mesoscale lenses with an overall size up to several mm. These include mm sized refractive microlenses, cylindrical and Fresnel lenses. It was made possible by real-time synchronization linear stages and galvo-scanners for rapid (several mm/s translation velocity) continuous writing. Mesooptical elements were produced in a single technological step showing the simplicity and potency of 3DLL. Qualitative and quantitative characterization of mesooptical elements was performed, their optical resiliency (LIDT – Laser Induced Damage Threshold) was assesed. The experimental work proves the 3DLL as suitable technique for the fabrication of diverse mesooptical elements and their function to be practically applicable for light flow, imaging and material processing. References [1] L. Jonušauskas, S. Juodkazis, and M. Malinauskas, "Optical 3D Printing: Bridging the Gaps in the Mesoscale," J. Opt. 20(5), 053001 (2018). [2] A. Žukauskas, V. Melissinaki, D. Kaškelytė, M. Farsari, and M. Malinauskas, "Improvement of the Fabrication Accuracy of Fiber Tip Microoptical Components via Mode Field Expansion," J. Laser Micro. Nanoeng. 9(1), 68-72 (2014). [3] T. Gissibl, S. Thiele, A. Herkommer, H. Giessen, "Two-Photon Direct Laser Writing of Ultracompact Multi-Lens Objectives," Nat. Photonics 10(8), 554-560 (2016). [4] E. E. Morales-Delgado, L. Urio, D. B. Conkey, N. Stasio, D. Psaltis, and C. Moser "Three-dimensional microfabrication through a multimode optical fiber," Opt. Express 25(6), 703-7045 (2017). [5] H. Ni, G. Yuan, L. Sun, N. Chang, D. Zhang, R. Chen, L. Jiang, H. Chen, Z. Gu, and X. Zhao, "Large-Scale Sigh-Numerical-Aperture Super-Oscillatory Lens Fabricated by Direct Laser Writing Lithography", RSC Advances 8(36), 20117-20123 (2018). [6] X. Chen, W. Liu, B. Dong, J. Lee, H. O. T. Ware. H. F. Zhang, and C. Sun, "High-Speed 3D Printing of Millimeter-Size Customized Aspheric Imaging Lenses with Sub 7 nm Surface Roughness," Adv. Mater. 30(18), 1705683 (2018).

Ultrafast laser lithography allows additive fabrication of 3D sub-micrometric size objects in various materials. Here we demonstrate significant new capabilities achievable with this approach by using hybrid organic–inorganic material as the initial medium for laser structuring, and adding a high-temperature post-fabrication treatment. Calcination at temperatures of up to 1500°C leads to decomposition of the organic component in the initial material, and sintering of the inorganic component into a stable matrix. This results in the final object composed purely of glass-ceramic material, and having volume and size significantly reduced in comparison to those of the initial object. Possibilities to control both the composition and degree of the thermal down-scaling will be demonstrated. The proposed new pathway to inorganic 3D nanoscale objects and structures is easy to implement, and allows one to significantly surpass the spatial resolution and feature size achievable using laser lithography only. We study optical properties of transparent inorganic microstructures and optimize them for specific photonic functions. In the future it may be useful in space and defense-related areas for realization of chemically and thermally resilient photonic components, such as narrow-band IR emitters and optical sensors to be used in nuclear power plants and other harsh environments. Reference D. Gailevicius, V. Padolskyte, L. Mikoliunaite, S. Sakirzanovas, S. Juodkazis, and M. Malinauskas, ”Additive-Manufacturing of 3D Glass-Ceramics down to Nanoscale Resolution,” Nanoscale Horiz., 10.1039/C8NH00293B (2019), online first.

Micro-optics have emerged as a cost-effective solution for increasing the photon collection efficiency of optoelectronic systems. By placing a microlens or microlens array (MLA) on top of the active area of a solar cell or photodetector, sustained improvements of up to 50% in the quantum efficiency of these devices have been demonstrated. However, current fabrication technologies for micro-optics can be limited in throughput, attainable geometries, fill-factor (FF) or range of suitable substrates. In this talk, I will present laser catapulting (LCP), a novel maskless laser additive manufacturing technique capable of customized and in-situ fabrication of polymeric micro-lenses over planar, curved and flexible substrates. LCP is based on a two-step process. First, a single laser shot is used to transfer a microdisk from a solid donor film directly to the area of interest on the optoelectronic device. Second, a thermal reflow process converts the disks into high-quality microlenses that exhibit almost perfect smoothness. Notably, closely packed MLA with a 100% FF can be obtained, not possible with standard direct-write methods such as inkjet printing or microdispensing. Furthermore, precise, accurate and high-throughput fabrication of lenses with different focusing power and geometries –spherical, cylindrical or even triangular – can be realized by simply adjusting laser parameters such as laser fluence or beam shape. I will present an in-depth experimental characterization of LCP, discuss the advantages and pitfalls of this technology and illustrate them with several applications, including enhancing the performance of single-photon avalanche diode (SPAD) arrays for super-resolution microscopy.