This PDF file contains the front matter associated with SPIE Proceedings Volume 12874, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

3D nanofabrication via Two-Photon Polymerization (TPP) provides a unique capability of flexibly fabricating complex structures over 1D-3D dimensions and µm-cm scales with resolutions below 100 nm. In the past years, the Laser-Assisted Nano Engineering (LANE) Group at the University of Nebraska-Lincoln (UNL) has been working closely with the Laboratory of Laser Energetics (LLE) in developing practical TPP approaches to fabricating various target structures for Inertial Confinement Fusion (ICF). At the same time, fuel capsules for ICF experiments should be inspected for surface and wall-embedded defects. Plastics materials [e.g., for example polystyrene (PS)] are the common materials used to make fuel capsules. However, during their manufacturing, capsules usually contain defects (vacuoles) embedded inside the shell walls, which may distort the implosion processes and influence the ICF performance of the capsules. The size of vacuoles is usually in a range from 100 to 2000 nm. Coherent anti-Stokes Raman scattering (CARS) microscope offers the capabilities of inspecting and characterizing the capsule defects. Moreover, cryo-CARS microscopy was developed to explore how fuel isotope distributed inside target when icing that could not be diagnosed before.

In this work, we review our recent results demonstrating the effectiveness of pulsed laser irradiation to fabricate nanostructures on various substrates, which are then used to enhance the Hydrogen Evolution Reaction (HER). Femtosecond (fs) laser pulses were used to fabricate nanostructures directly on nickel and iron sheets, while nanosecond laser pulses were used to fabricate nanostructures on Ni foam (NF) substrates via pulsed laser deposition. Electrodeposition was further employed complementary to the fs laser-surface direct nanostructuring to deposit Ni nanoparticles on top of the laser-modified nanostructures. A thorough electrochemical, structural, and morphological comparison has been conducted between laser-nanostructured and flat (i.e., untreated) Ni and Fe electrodes. In addition, the Ni-deposited (with PLD) NF electrodes were compared to an untreated NF electrode. The prepared electrodes show enhanced electrochemical characteristics and superior performance in HER. Morevover, the laser-nanostructured and electrodeposited electrodes were found to be as much as 4.6 times more efficient in actual Hydrogen production conditions. We propose that scaling up in the fabrication of such nanostructured electrodes should be pursued to address global energy and environmental concerns.

Lasers are known to be extremely versatile tools suitable both for the synthesis and modifications of numerous nanomaterials with unique and extremely interesting optical properties suitable for a wide range of applications in various fields ranging from optics and photonics to medical applications. Efficient control over these processes is still challenging and often requires numerical simulations because of the complex interplay of many physical and chemical processes involved that depend on the combination of both material properties and laser parameters. To simulate these processes, multi-physical modeling should be used including electromagnetic, thermal, mechanical, and chemical effects taking place at several time and space scales. Depending on the experimental conditions, nanoparticles can be formed, grow, aggregate, or on the contrary decay, so that a set of transient variations often take place, particularly when multi-pulse laser irradiation is applied. In the case of short and ultra-short laser pulses, strongly non-linear and time-dependent processes play a role involving not only ionization but also phase transitions, acoustic vibrations, shock waves, as well as void formation, and cavitation. If a considerable energy is released in a very short time, firstly aggregates decay, then nanoparticles are fragmented. Here, based on numerical calculations, the roles of several above-mentioned effects are analyzed. The performed simulations can be used for a better understanding of laser interactions with nanoobjects.

Laser-written Nitrogen Vacancy (NV−) centers are combined with transfer-printed GaN micro-lenses to increase fluorescent light collection by reducing total internal reflection at the planar diamond interface. We find a 2x improvement of fluorescent light collection using a 0.95 NA air objective at room temperature, in agreement with FDTD simulations. The nature of the transfer print micro-lenses leads to better performance with lower Numerical Aperture (NA) collection, as confirmed by results with a 0.5NA air objective which show improvement greater than 5x. The approach is attractive for scalable integrated quantum technologies.

Harnessing the distinctive attributes of three-dimensional auxetic scaffolds in applications related to tissue engineering and regenerative medicine injects fresh momentum into these domains. In this study, we present our findings regarding the creation and characterization of three-dimensional auxetic scaffolds tailored for tissue engineering applications. These scaffolds leverage the well-established re-entrant hexagonal geometry (bowtie) and are manufactured through multiphoton lithography utilizing the organic-inorganic photopolymer SZ2080. Employing in-situ scanning electron microscopy, micro-indentations, and nano-indentation experiments, we meticulously analyze the photocurable resin SZ2080 and the resultant scaffolds. Despite SZ2080 being inherently rigid with a positive Poisson’s ratio, our investigation reveals that the scaffolds exhibit a negative Poisson’s ratio and remarkable elasticity attributed to their specific architecture. Subsequently, we employ mouse fibroblasts to seed the scaffolds, demonstrating their capacity to efficiently infiltrate and proliferate within, conforming to the scaffold's structure to meet the cells' needs. Furthermore, the scaffold's architecture imparts a directional preference to the cells, a crucial factor in various cell-based applications within regenerative medicine. Our research lays the groundwork for the practical utilization of 3D auxetic metamaterials as cutting-edge, adaptable scaffolds in the realm of tissue engineering.

Since Multiphoton Lithography (MPL) is applied as an additive manufacturing technique for the fabrication of operational microsystems, the need to predict the mechanical response of the fabricated structures emerges. This work focuses on determining the Young’s Modulus of structures fabricated via MPL. With this objective in mind, two series of experiments were designed and conducted: the first one for the determination of the factors whose impact is significant, and the second one for generating a dataset used in the training of a machine learning tool that will define the suitable set of fabrication parameters for the fabrication of a structure with desired Young’s Modulus.

Combining ultrashort laser pulses at an interface can generate an informative signal called SFG (sum frequency generation). SFG can reveal information about an interface with a thickness of nanometers. Such information can be utilized for instance to understand surface properties under the catalytic process. Herein, we utilized the second-order susceptibility generated from the gold surface to monitor the redox mechanism of gold. Gold is a standard metal surface that is commonly utilized to study surface redox processes such as water oxidation and hydrogen production processes. We found that the redox behavior of gold surfaces, using SFG, adds new mechanistic dimensions to the known mechanism from electrochemistry. For instance, in an acidic medium, two different gold oxides can be formed, the primary one is completely reversible, while the secondary one is not. Such a redox mechanism can lead to stratified gold layers, in which buried gold oxides can be formed. Such stratified structure has been also confirmed by the complementary XPS technique. A similar gold redox mechanism has been found in the basic medium; however, SFG shows that top-atomic gold surface layers can be more active than those in an acidic medium, which can illustrate the catalytic activity of the gold surface layer in the basic medium more than those in the acidic medium. All these implications revealed by SFG about gold will be discussed in my presentation along with the expected challenges to electro-catalysis processes.

Recently, InAs/GaAs nanostructures assembled by cyclic, alternating deposition of submonolayer (SML) InAs and monolayer GaAs using Molecular Beam Epitaxy (MBE) has been gaining interest for their novel and highly tunable optoelectronic properties. Furthermore, it has recently been revealed that a growth transition during SML growth leads to two types of nanostructures: 2D islands and 3D structures. Although the highly tunable properties of SML nanostructures make them strong candidates for spintronics applications, investigations on the spin properties of SML nanostructures are lacking. In this study, the spin properties of SML nanostructures are investigated using optical spin injection and detection measurements. Spins are injected into the SML nanostructures using the optical selection rules in GaAs for Circularly Polarized Light (CPL) excitation, whereas spin state in the SML is detected by measuring the right (σ⁺) and left (σ^- ) CPL intensity components of the luminescence. The degree of CPL is estimated by quantity P = [I(σ⁺ ) - I(σ^- )]/[I(σ⁺ ) + I(σ- )], where I(σ^± ) is the luminescence intensity for the σ^± component. The quantity P is directly related to the spin state in the SML. Our experiments have yielded a relatively high P = 6% for the 3D SML nanostructures, whereas a relatively low P = 1% for the 2D SML nanostructures. The difference may be attributed to the higher carrier confinement for 3D SML resulting in preservation of spin state and thus resulting to a higher P. These results reveal fundamental differences in the spin dynamics of 2D and 3D SML nanostructures.

The field of cancer nanomedicine is moving towards maturity thanks to innovative technologies and original nanomaterials. This is required to surpass the limitations of the previous generations of nanomedicines, such as biopersistence, experimental therapeutic approaches far from the clinic, long-term toxicity of heavy metals and other compounds used in nanoparticles. Here we show how laser processing is playing a crucial role for the realization of an emerging class of advanced inorganic nanomedicines based on nanoscale alloys. Nanoparticles of Au-Fe, Au-B, Fe-B and Fe-Ag alloys have been obtained by laser-assisted synthesis, even if most of them are thermodynamically unstable. These nanoalloys exhibited multiple appealing properties for imaging and therapy of cancer and have been designed to address the issues of previous nanostructured compounds for the treatment of cancer, by endowing mid-term biodegradability, complementarity and synergy of the theranostic functions. Therefore, laser technologies are contributing to the addition of new nano-tools for addressing the treatment of cancer with higher efficacy, feasibility and tolerability.

Photoacoustic Imaging (PAI) has emerged as a powerful imaging technique that combines advantages of optical absorption contrast with the ability to penetrate deep into biological tissues using ultrasound waves. Exogenous chromophores, including light-absorbing nanoparticles (NPs), can significantly enhance the photoacoustic response and provide photoacoustic contrast for various regions in organism. We recently introduced laser-synthesized TiN NPs as a promising alternative plasmonic nanomaterial, having exceptionally high optical absorption in the window of biological tissue transparency. In this study, we continue our evaluation of laser-synthesized TiN NPs as a contrast agent for PAI by comparative studying of optical and photoacoustic response of tissue-mimicking phantoms containing TiN NPs. We demonstrated that laser-synthesized TiN NPs preserve their superior photoacoustic performance in the conditions of tissue-like media. Our results confirm high potential of TiN NPs to serve as an effective exogenous contrast agent for PAI.

Using Pulsed Laser Deposition (PLD), Zr films were deposited on silicon with laser wavelengths of 1064 nm and 532 nm, at substrate temperatures of 25 °C, 300 °C, and 500 °C, and fluences of 0.25, 0.5, and 1.0 J/cm². The 1064 nm wavelength yielded smoother films, with surface roughness growing at higher fluences. The 300 °C temperature was ideal for crystal quality. Analyses through XRD, SEM, and AFM showed unique morphologies due to laser variables. Computations using a thin film growth model matched the empirical data, underscoring the factors critical to Zr film deposition and guiding PLD optimization for superior film quality.