This PDF file contains the front matter associated with SPIE Proceedings Volume 11812, including the Title Page, Copyright information, and Table of Contents.

We review recent transformative advances in materials design, synthesis, and processing as well as device engineering for the utilization of organic materials in hybrid electro-optic (EO) and optical rectification (OR) technologies relevant to telecommunications, sensing, and computing. End-to-end (from molecules to systems) modeling methods utilizing multi-scale computation and theory permit prediction of the performance of novel materials in nanoscale device architectures including those involving plasmonic phenomena and architectures in which interfacial effects play a dominant role. Both EO and OR phenomenon require acentric organization of constituent active molecules. The incumbent methodology for achieving such organization is electric field poling, where chromophore shape, dipole moment, and conformational flexibility play dominant roles. Optimized chromophore design and control of the poling process has already led to record-setting advances in electro-optic performance, e.g., voltage-length performance of < 50 volt-micrometer, bandwidths < 500 GHz, and energy efficiency < 70 attojoule/bit. They have also led to increased thermal stability, low insertion loss and high signal quality (BER and SFDR). However, the limits of poling in the smallest nanophotonic devices—in which extraordinary optical field densities can be achieved—has stimulated development of alternatives based on covalent coupling of modern high-performance chromophores into ordered nanostructures. Covalent coupling enables higher performance, greater scalability, and greater stability and is especially suited for the latest nanoscale architectures. Recent developments in materials also facilitate a new technology—transparent photodetection based on optical rectification. OR does not involve electronic excitation, as is the case with conventional photodiodes, and as such represents a novel detection mechanism with a greatly reduced noise floor. OR already dominates at THz frequencies and recent advances will enable superior performance at GHz frequencies as well.

We report on the electrical properties of a series of molecular rectifiers based on benzalkylsilane molecules in self-assembled monolayers (SAMs) anchored to silicon substrates with a native layer of SiO2. Mixed SAMs were formed via co-absorption where known amounts of aliphatic silane-based impurities were included into the rectifying SAMs. We discovered that in spite of the fact that the degree of order within the SAMs decreased upon dilution the impurity (3-aminopropyl)triethoxysilane enhanced the rectification for several SAMs. The largest change resulted in a three-fold increase for an average rectification of 4500; the highest reported rectification for SAMs assembled on silicon to date. We attribute this novel behavior to a new molecular configuration within the SAM that allows more efficient coupling between the delocalized electrons of the SAM and the device electrode. Understanding how to optimize SAMs will allow for more functionable, integrable and cost-efficient devices.

Optical forces generated by interaction between light and biomaterials induce an optical waveguide, leading to a deep penetration of light in a scattering suspension. In contrast, we report on the optical vortex induced exotic nonlinear phenomena not only the conventional self-trapping effects. A 532 nm continuous-wave right-/left-handed first-order optical vortex was focused to be an annular spot with a diameter of 40 um in cyanobacteria suspensions, where their nonlinearity was controlled by appropriately mixing seawater and glycerol. The incident optical vortex underwent strong self-defocusing effects in the suspensions with a high mixing ratio of glycerol, resulting in the creation of the dark soliton. The spatial symmetry breaking of the incident optical vortex further occurred in the moderate mixing ratio, manifesting the modal instability effects. Furthermore, the broken optical vortex then rotated towards a clockwise/anticlockwise direction assigned by its handedness.

Among the existing realizations of microscopic motile devices, photonically propelled nano- and microparticles are particularly advantageous. Their features pave the way for applying them in large numbers, e.g., as constituents of novel active materials with exceptional properties. However, the recently proposed photonically propelled particles have so far been studied only partially on the single-particle level so that their interesting collective dynamics remains unexplored. This talk will address this issue by presenting methods that allow to proceed from the single-particle motion of motile particles to their collective dynamics. It will focus on analytical modeling and computer simulations as well as their application to photonically propelled nano- and microparticles. Furthermore, it will present results, including unexpected pattern formation and transport effects, obtained by these methods for system sizes and particle numbers that are not yet accessible by experiments.

Surface bending strains in various flexible films is quantitatively analyzed by a surface-labeled grating method with a single-nanometer resolution. The real-time strain analysis we achieved has multiple benefits: high resolution, precision, and a wide range of measurable materials. The reliability of the measurements was confirmed using the modified Elastica theory. This method revealed that the cracking of hard coatings on the surface of PET films occurred at surface strains exceeding 1.45%, regardless of the film thickness and curvature. The multilayering of two PET layers with a soft PDMS layer between them reduced the surface bending strain by 50% compared with that of a single-layer film with the same thickness. This triple-layer film successfully suppressed the cracking of the hard coating and the breakdown of the OTFT. The surface-labeled grating method, therefore, is a practical tool that allows the analysis of surface bending strain in the elaborately designed materials.

Photo-induced reversible surface reliefs in azo-polymers act potentially as an important role to realize rewritable optical data storage with high density, and light driven micro/nanorobots. Optical vortex possesses a ring-shaped spatial profile and an orbital angular momentum, associated with its helical wavefront. Going beyond the conventional surface reliefs, we here report on a myriad of surface structures, such as a nano/micron scale chiral relief and a flower-shaped relief, via single photon or two photon absorption, created by employing versatile structured light fields with orbital angular momentum in a continuous-wave and a femtosecond regions. Such structured light induced exotic surface reliefs should provide us new fundamental physical insights, associated with light-matter interaction in the azo-polymer film, and they will also open the door towards advanced technologies, such as ultrahigh density optical data storages.

Among the numerous propulsion mechanisms developed in the past to self-propelled nano- and micro particles, light-driven machines are most promising, since they enable a natural spatio-temporal control of the motion. We report a novel fuel-free propulsion mechanism induced by an external light stimulus. The actuation relies on refraction of light, while the net propulsion force emerges from an asymmetric particle shape and a symmetry-broken refractive index profile. Two-photon polymerization is employed for fabrication of the artificial machines, whose geometries and refractive index profiles are optimized with the help of numerical simulations. We demonstrate the directional movement of refractive light-propelled particles, and the increased performance of artificial refractive index machines.

Azobenzene molecules have attracted important interest for photodynamic drug release and therapy applications. Often, their impact on the environment is directly associated to the photoinduced mechanical deformation of the molecule (when transferring from its Trans form to the Cis form). In the present talk, we demonstrate that the chemical impact of this transformation (pH, toxicity, etc.) also must be considered. We shall describe our work on the development of an optical control method of biological membranes based on the photoisomerization process. On the example of E-coli bacteria, we shall show that the isomerization process can indeed be used to control their behavior, but the changes in pH and toxicity are also playing important roles. Interestingly, while there are still many open questions, our preliminary results point out on the possibility of controlling protonic pump channels in a selective way.

The optical sectioning images of volumetric biological sample was obtained by varifocal metalens with Moiré effect in fluorescence microscopy system in conjunction with telecentricity and HiLo image processing method. The varifocal metalens is capable of changing the focal depth ranging from 10 mm to 125 mm by tuning the relative angle between its paired metasurfaces. The standard resolution target and fluorescent mircrosphere are imaged and analyzed; its lateral resolution and optical sectioning capability are 2.46 μm and 7.5 μm, respectively. Our study offers a demonstration, a solid foundation, for developing more compact optical microscopy systems based on metasurface optics.

Plasmonic nanostructures enable us to enhance light fields at nanoscale beyond diffraction limit, thereby offering us metamaterials and plasmonic crystals to realize exotic light-matter interactions, including negative refractive index, invisible cloaking, and perfect absorption. We here demonstrate, for the first time to be the best of our knowledge, the creation of a single water microdroplet with a single plasmonic Au nanoparticle (~150 nm) core (plasmonic nanocore) by employing the optical vortex induced forward transfer. The microdroplet can be easily trapped to form a single plasmonic nanocore on a receiver substrate with a spatial resolution beyond the diffraction limit. Going beyond conventional fabrication processes for plasmonic structures, such as lithography technologies based on electron and ion beams, such plasmonic nanocore formation in a water microdroplet should offer us new fabrication technology for plasmonic structures.

We review our work on multi-photon 3D laser micro- and nanoprinting of stimulus-responsive multi-material architectures. We emphasize (i) work for actuation under aqueous conditions and (ii) work for actuation under ambient conditions. Part (i) is based on hydrogels and has previously been published (M. Hippler et al., Nature Commun. 10, 232 (2019)). Here, the degree of cross-linking can be controlled by laser exposure dose (“gray-tone lithography), allowing us to obtain multi-material architectures from just a single photoresist. The Young’s modulus and the thermal expansion coefficient can be different by as much as about a factor of ten. Part (ii) is based on liquid-crystal elastomers (unpublished). Here, during the 3D printing process and in a dedicated sample cell, we apply a quasi-static electric field, allowing us to define the direction of the liquid-crystal director for each voxel in three dimensions. Large reversible and repeatable actuation is obtained.

Multi-material 3D printing has attracted much attention due to its ability to produce functional 3D structures. We have developed several types of multi-material micro stereolithography systems including multi-tank type and single cylinder type. Recently, a multi-material micro stereolithography system based on single-photon polymerization using multiple droplets was also developed. In the multi-material micro stereolithography system, several types of photocurable resins are stored on a palette that is moved by a translation stage. Heterogeneous 3D microstructures are formed by accumulating each layer while exchanging the resins. In this system, two cleaning tanks are installed to prevent contamination of resin. Additionally, to prevent inclusion of air bubbles into the 3D-printed parts, the platform supporting the 3D-printed part was moved in horizontal plane. As a result, air bubbles were successfully pushed out of the fabrication area. Using several types of photocurable resins with different colors, multicolor 3D microstructures such as cubes and lattices were fabricated. By adjusting the number of accumulated layers, the color of the 3D-printed structure can be controlled. These multi-material micro stereolithography systems will be useful for producing functional microdevices including microfluidic elements, micromachines and scaffolds.

Two-photon polymerization (TPP) enables us to fabricate three-dimensional structures with feature sizes beyond the diffraction limit. In TPP, since near-infrared femtosecond pulsed laser has been used for two-photon excitation, photo-initiators are added into a resin to trigger the TPP reaction. Here, we propose a photo-initiator free TPP by utilizing monomer’s intrinsic absorption in the deep-UV (DUV) region. Chemical bonds in monomer molecules are directly two-photon-excited with a visible femtosecond pulsed laser at 400-nm wavelength. We fabricated 3D nano-structures of acrylic oligomer, inorganic materials, and biomaterials without a photo-initiator. Raman spectroscopy study clarified chemical structure changes upon DUV two-photon excitation.

The ability to fabricate your own microfluidic devices provides flexibility to alter the exact design of the device as the project develops. Here we present a concise fabrication process of reusable microscope-compatible microfluidic devices for biophotonic applications. The method requires commonly available components, such as a 3D printer or 3D pen, heat plate, sonicator, PDMS, and acetone. For high NA objective’s measurements, a cover glass can be inserted and replaced from the main microfluidic chamber. For our studies of the controlled bacterial biofilm formation, a laser beam is also delivered from the side of the microfluidic device with a fiber-coupled laser or from the bottom through an objective.

We study the mechanisms of the photomechanical response of dye-doped polymers and liquid crystal elastomers by characterizing the stress/strain response function to modulated light of a variety of material compositions with the specific goal of optimizing the photomechanical response Figure of Merit (FOM), which quantifies the efficiency with which light energy is converted to mechanical work. We discuss experiments that vary the parameters, which define the FOM to study the underlying mechanisms. Large and dramatic length changes and bending angles are commonly observed in materials with a small Young’s modulus even when the light-induced stress is small. However, useful devices require large forces, which may not always lead to large displacements in stiff materials. We use the concept of a photomorphon, the smallest photomechanical material element, to guide in the design of the most efficient materials and describe the photomechanical analog of the optical transistor.

In this presentation, we discuss enhancement of photo-orientation of azo-dye in films of polymer by surface enhanced visible absorption (SEVA) of the dye in the vicinity of Gold nanoantennas. The dye undergoes shape and orientation change; i.e. isomerization and reorientation, upon polarized light absorption; and the observation of enhanced photo-orientation by SEVA is done by photo-induced birefringence (PIB) experiments, since the signal detected from PIB experiments is directly proportional to the extinction coefficient of the dye. Both the dye’s absorption and photoorientation are enhanced by the presence of the plasmonic nanoantennas.

In recent years, Argentina and countries of the region, have suffered epidemics associated with arboviruses, mainly Dengue and more recently Zika and Chikungunya. On the other hand, since the worldwide pandemic of SARS-CoV-2 (COVID-19), people’s health and the economic support of their countries have been seriously affected. It is necessary to have economic and faster diagnostic tools that allows evaluating samples of patients with symptoms. With this objective, diagnostic systems called point of care have been recently developed. These systems are defined as medical diagnostic testing at or near the point of care (that is, at the time and place of patient care). Specifically, in this work, a bio-photonic device has been developed. This instrument is able to detect certain diseases by means of a luminescence spectral analysis. This method can be conducted for saliva samples. The system consists in the fluorescence signal detection generated by a specific probe of the target viral genome, that coupled to isothermal amplification reaction, allowing the detection of the pathogen in the sample. The device excites the sample to be analyzed with light (led or semiconductor lasers with specific wavelengths) thus it triggers a spontaneous emission of the fluorophore bound to the specific probe. The emitted fluorescence is suitably filtered using interferential filters. These filters limit the spectral regions and allow discriminating the analysis band. Under these conditions, a signal is registered in a built-in detector and, depending on the signal level, define the case as positive or negative. All the analysis is done autonomously inside the developed device through an integrated control system and it is connected to a portable device to show the results wirelessly.