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Lasers are instrumental in enabling precise processing and fostering the development of new technologies. Particularly, ultrafast lasers, due to their unique interaction with matter, can achieve not only exceptional spatial precision but also meticulously determine the degree of modification. A prime example of this is laser‐based 3D printing through multi‐photon lithography (MPL). This approach remarkably enables the printing of true 3D structures at the micro‐ and nanoscale, without the need for masks or cumbersome tools, simply by using computer‐aided designs. Owing to these unique capabilities, MPL has emerged as a powerful manufacturing technique across various multidisciplinary fields. The ongoing growth in MPL's utilization has led to notable advancements in printing highly complex structures on different substrates, as well as improvements in resolution and throughput, and the development of novel photosensitive materials, which impressively facilitated MPL's expansion into broader fields over the last few years. In this perspective article, the aim is to highlight these advancements and recent trends in MPL. The current challenges of MPL will be explored, which need to be addressed to ensure its further integration into advanced Additive Manufacturing at the micro‐ and nanoscale. The future perspectives and opportunities of MPL as a laser‐based 3D printing approach will also be discussed. [ABSTRACT FROM AUTHOR]

The rapid development of additive manufacturing has fueled a revolution in various research fields and industrial applications. Among the myriad of advanced 3D printing techniques, two‐photon polymerization lithography (TPL) uniquely offers a significant advantage in nanoscale print resolution, and has been widely employed in diverse fields, for example, life sciences, materials sciences, mechanics, and microfluidics. More recently, by virtue of the optical transparency of most of the resins used, TPL is finding new applications in optics and photonics, with nanometer to millimeter feature dimensions. It enables the minimization of optical elements and systems, and exploration of light‐matter interactions with new degrees of freedom, never possible before. To review the recent progress in the TPL related optical research, it starts with the fundamentals of TPL and material formulation, then discusses novel fabrication methods, and a wide range of optical applications. These applications notably include diffractive, topological, quantum, and color optics. With a panoramic view of the development, it is concluded with insights and perspectives of the future development of TPL and related potential optical applications. [ABSTRACT FROM AUTHOR]

Optical activity (polarization rotation of light) is one of the most desired features of chiral media, as it is important for many polarization‐related applications. However, in the THz region, chiral media with strong optical activity are not available in nature. Here, a chiral metamaterial (CMM) structure composed of pairs of vertical U‐shape resonators of "twisted" arms is studied, and it is revealed that it demonstrates large pure optical activity (i.e., optical activity associated with negligible transmitted wave ellipticity) in the low THz regime. The experimental data show polarization rotation up to 25° for an unmatched bandwidth of 1 THz (relative bandwidth 80%), from a 130 µm‐thickness structure, while theoretical optimizations show that the rotation can reach 45°. The enhanced chiral response of the structure is analyzed through an equivalent RLC circuit model, which also provides simple optimization rules for the enhancement of its chiral response. The proposed chiral design allows for easy fabrication via direct laser writing (DLW) and electroless metal plating, making the associated structures suitable candidates for polarization control applications. [ABSTRACT FROM AUTHOR]

A micro-optical Fabry-Perot cavity fabricated by non-linear laser lithography on the endface of a standard telecom fiber is tested here as a microsensor for identifying oily liquids. The device operates within the 1550 nm spectral region, while the spectra recorded in reflection mode correlate to the refractive index of the oily liquids used, as well as, to the diffusion dynamics in the time domain of the oily samples inside the porous photo-polymerized sensing head. The operation of the microresonator sensing probe is explained by using a three-layer Fabry-Perot model and basic diffusion physics to estimate diffusivities for three series of refractive index matching oils with different chemical compositions that had been used in those experiments. The distinct spectro-temporal response of this sensing probe to the different oil samples is demonstrated and discussed. [ABSTRACT FROM AUTHOR]

We report on the design, modeling and fabrication by multi-photon polymerization of a complex medical fluidic device. The physical dimensions of the built micro-valve prototype are compared to those of its computer-designed model. Important fabrication issues such as achieving high dimensional resolution and ability to control distortion due to shrinkage are presented and discussed. The operational performance of both multi-photon and CAD-created models under steady blood flow conditions was evaluated and compared through computational fluid dynamics analysis. [ABSTRACT FROM AUTHOR]

A novel method to overcome the problem of accurately centering microoptical components built by direct laser writing on the tip of a single mode optical fiber is presented, and it includes employing mode field expansion. A hybrid microoptical component consisting of an aspherical and a conical lens integrated into a single monolithic element has been fabricated at the end-face of a fiber using the technique of direct laser writing of photopolymers. The optical performance of the fabricated microstructures has been measured experimentally. We show that optical properties of Gaussian and Bessel beams can be easily tuned by adjusting the geometrical parameters of fiber-tip microoptical elements. In addition, we experimentally demonstrate the increase of propagation distance of a Bessel beam five-fold, using the fabricated microoptical element. This improvement in the fabrication method of fiber-tip microoptical elements can be used in the manufacturing of integrated micro-optical devices for optical tweezing, laser micromachining and long focal depth optical systems. [ABSTRACT FROM AUTHOR]

For a great variety of research fields extending from photonics to tissue engineering applications, the requests for the construction of three-dimensional structures with high resolution grow more and more imperative. Towards this aim, the direct laser writing technique by multi-photon polymerization, due to its unique properties and characteristics, has proven to be an indispensable tool to high accuracy structuring and has been put on the map as an emerging technology for scaffold 3D printing. In the present review, the basic principles of multi-photon polymerization are presented, the experimental set-up requirements are described and the employed materials demands are thoroughly mentioned as well as the most representative examples of the recent developments in the field. [ABSTRACT FROM AUTHOR]