A pilot study on laser 3D printing of inorganic free-form micro-optics is experimentally validated. Ultrafast laser direct-write (LDW) nanolithography is employed for structuring hybrid organic-inorganic material SZ2080TM followed by high-temperature calcination post-processing. The combination allows the production of 3D architectures and the heat-treatment results in converting the material to inorganic substances. The produced miniature optical elements are characterized and their optical performance is demonstrated. Finally, the concept is validated for manufacturing compound optical components such as stacked lenses. This is an opening for new directions and applications of laser-made micro-optics under harsh conditions such as high intensity radiation, temperature, acidic environment, pressure variations, which include open space, astrophotonics, and remote sensing.

3D printed objects was first presented by Maruo in a technology-opening article in 1997, [2] where the use of this technology to fabricate micro-optics was also envisaged. The serial writing method of this technique offered flexibility for freeform fabrication, but was limited by its throughput. [3] It took some years for the technology to mature from proof-of-principle level to additive manufacturing as a tool for efficient and reliable fabrication in the modern lab. [4][5][6] Though the first micro-optical elements were demonstrated as early as 2006, [7] the major efforts and results only started to emerge in 2010, [8,9] together with the development of hybrid organic-inorganic materials, [10,11] and rapidly accelerated with the implementation of commercial 3D lithography systems. [12][13][14] By 2020, ultrafast laser 3D printing, also known as two-photon polymerization (TPP or 2PP), multiphoton lithography (MPL), [15][16][17] or simply laser direct writing (LDW), also in literature referenced as direct laser writing (DLW), [18] ) was already an established technique for routine fabrication of diverse micro-optical single elements, stacked components, and integrated devices. [19][20][21] The latest advances in the 3D printing of free-form micro-optics are enhanced by optical grade materials of high refractive index (n) polymers, [22] high-performance hybrids, [23] and optically active [24] or pure inorganic glasses. [25] Figure 1 shows the development of the technique in terms of published papers and citations, defining an "innovator stage" of the technology followed from 2015 by the "early adopters stage." Examples of micro-optical elements fabricated using MPL and the growth in the complexity of the structures that can be achieved by this technique are also shown in Figure 1.The advances in this scientific field attracted the attention of the related laser-assisted precision additive manufacturing industry. First, in 2007 Nanoscribe GmbH and in 2008 Workshop of Photonics established companies oriented toward commercialization of this technology aimed at general wide angle application fields. While in 2013, Multiphoton Optics GmbH and Femtika UAB were established and made micro-optics a significant part of their targeted applications. Finally, in 2017, Vanguard Photonics GmbH manufactured dedicated MPL equipment for micro-lenses and wire bond production. Other companies targeting more diverse applications have continued to emerge, such as UpNano established in 2018, and focusing mostly on biomedical applications yet also offering solutionsThe field of 3D micro-optics is rapidly expanding, and essential advances in femtosecond laser direct-write 3D multi-photon lithography (MPL, also known as two-photon or multi-photon polymerization) are being made. Micro-optics realized via MPL emerged a decade ago and the field has exploded during the last five years. Impressive findings have revealed its potential for beam shaping, advanced imaging, optical sensing, integrated photonic circuits, and much more. This is suppo...

Structuring light attracts continuous research effort due to its impactful applications in optical information and communications, laser material processing, optical imaging, or optical manipulation of matter. In particular, femtosecond laser direct writing of photoresists is a technology dedicated to the creation of optically isotropic free-form 3D micro-optical elements with size, spatial resolution, and surface quality that qualify to demanding integrated optics needs. Here, we report on the design, production, and characterization of dielectric metasurface birefringent optical retarders made from femtosecond laser 3D printing technology whose polarization conversion efficiency is more than 10 times larger than that previously reported Wang et al., Appl. Phys. Lett. 110, 181101 (2017)]. As the flexibility of the fabrication process allows considering arbitrary orientation of the artificially engineered optical axis, these results open up for 3D printed geometric phase optical elements.

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Direct laser writing three-dimensional nano-lithography is an established technique for manufacturing functional 3D micro- and nano-objects via non-linear absorption induced polymerization process. In this Chapter an underlying physical mechanisms taking place during nano-confined polymerization reaction, induced by tightly focused ultra-short laser pulses, are reviewed and discussed. The specialattention is paid on the effects that directly impact structuring resolution and minimum achievable feature size. Analysis of possible photo-initiation mechanisms as contributing multi-photon absorption and avalanche ionization in pre-polymers under diverse exposure conditions (wavelength, pulse duration) is presented. Feasible structuring of pure (non-photosensitized) and functional nanoparticles doped polymer precursors is justified and benefits of such materials/structures for microoptics, photonics and cell scaffolds are highlighted. The influence of temperature effects (induced by writing process itself or determined by ambient conditions) on polymerization process, observed in different pre-polymers under diverse exposure regimes is outlined. The further adjustment of the structuring resolution is possible via precise control of light polarization and diffusion assisted radical quenching. The work is concluded with a brief outlook on future challenges and perspectives related to refinement of 3D ultra-fast laser lithography fabrication process in the means of application of diverse post-processing methods and research into novel photo-curable materials including inorganic ones.

Direct laser writing three-dimensional nano-lithography is an established technique for manufacturing functional 3D micro-and nano-objects via non-linear absorption induced polymerization process. In this Chapter an underlying physical mechanisms taking place during nano-confined polymerization reaction, induced by tightly focused ultra-short laser pulses, are reviewed and discussed. The special attention is paid on the effects that directly impact structuring resolution and minimum achievable feature size. Analysis of possible photo-initiation mechanisms as contributing multi-photon absorption and avalanche ionization in pre-polymers under diverse exposure conditions (wavelength, pulse duration) is presented. Feasible structuring of pure (non-photosensitized) and functional nanoparticles doped polymer precursors is justified and benefits of such materials/structures for microoptics, photonics and cell scaffolds are highlighted. The influence of temperature effects (induced by writing process itself or determined by ambient conditions) on polymerization process, observed in different pre-polymers under diverse exposure regimes is outlined. The further adjustment of the structuring resolution is possible via precise control of light polarization and diffusion assisted radical quenching. The work is concluded with a brief outlook on future challenges and perspectives related to refinement of 3D ultra-fast laser lithography fabrication process in the means of application of diverse post-processing methods and research into novel photo-curable materials including inorganic ones.

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