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1. 2D TiS 2 Layers: A Superior Nonlinear Optical Limiting Material

   https://doi.org/10.1002/adom.201700713  

   Varma, Sreekanth J. ; Kumar, Jitesh ; Liu, Yang ; Layne, Katherine ; Wu, Jingjie ; Liang, Chenglu ; Nakanishi, Yusuke ; Aliyan, Amir ; Yang, Wei ; Ajayan, Pulickel M. ; et al ( October 2017 , Advanced Optical Materials)

   The advancement in high power lasers has urged the requisite of efficient optical limiting materials for both eye and sensor protection. The discovery of atomically thin 2D transition metal dichacogenides with distinctive properties has paved the way for a variety of applications including optical limiting. Until recently, the optical limiting effect exhibited by 2D materials is inferior to the benchmark materials fullerene (C₆₀) and graphene. This article reports the optical limiting activity of the 2D transition metal dichalcogenide, titanium disulfide (TiS₂) nanosheets, using optical and photoacoustic z‐scan techniques. The 77% nonlinear optical limiting exhibited by the TiS₂sheets with 73% linear‐transmittance is superior to that of any other existing 2D dichalcogenide sheets, graphene, and the benchmark optical limiting material, C₆₀. The enhanced nonlinear response is attributed to the concerted effect of 2‐photon and the induced excited state absorptions. By using photoacoustic z‐scan, a unique tool developed to determine the nonlinear optical limiting mechanism in materials, it is found that the optical limiting exhibited by TiS₂2D sheets and graphene are mainly due to nonlinear absorption rather than scattering effects. These results have opened the door for 2D‐dichalcogenide‐materials‐based highly efficient optical limiters, especially at low fluences.

    

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2. Nonlinear Absorption in Plasmonic Titanium Nitride Nanocrystals

   https://doi.org/10.1002/adom.202201290  

   Sabzeghabae, Ariana Nushin ; Berrospe‐Rodriguez, Carla ; Wu, Chaolumen ; Mangolini, Lorenzo ; Aguilar, Guillermo ( November 2022 , Advanced Optical Materials)

   Titanium nitride nanoparticles have become a research interest due to their distinguished optical and photothermal properties. Furthermore, the search for nanoparticle solutions with tunable nonlinear optical properties for laser‐based applications is critical. More specifically, third order optical nonlinearities such as reverse saturable absorption, optical liming, and self‐focusing are important in the biomedical and electronics fields. The optical nonlinearities of titanium nitride plasmonic nanoparticles are investigated as a function of material concentration in water solutions. Furthermore, the effect of nanoparticle clustering on optical nonlinearities is investigated by fabricating micrometer‐sized clusters of ≈50 nm titanium nitride particles. These studies demonstrate that the nonlinear absorption coefficient increases linearly with concentration. However, clusters require higher concentrations compared to the freestanding nanoparticles to exhibit similar nonlinear absorption coefficient and optical density. Similarly, the optical limiting threshold for titanium nitride nanoparticles appears to be lower compared to the cluster solutions, which is impacted by the collective scattering of nanoparticles and high reverse saturable absorption. In addition, self‐focusing is observed in the continuous resonant regime. This study provides an in‐depth analysis of the nonlinear optical properties of titanium nitride, with relevant consequences for applications such as sensor protection and photothermal therapy.

    

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3. Role of chain architecture in the solution phase assembly and thermoreversibility of aqueous PNIPAM/silyl methacrylate copolymers

   https://doi.org/10.1039/d2py00254j  

   Linn, Jason D. ; Liberman, Lucy ; Neal, Christopher A. ; Calabrese, Michelle A. ( June 2022 , Polymer Chemistry)

   Stimuli-responsive polymers functionalized with reactive inorganic groups enable creation of macromolecular structures such as hydrogels, micelles, and coatings that demonstrate smart behavior. Prior studies using poly( N -isopropyl acrylamide- co -3-(trimethoxysilyl)propyl methacrylate) (P(NIPAM- co -TMA)) have stabilized micelles and produced functional nanoscale coatings; however, such systems show limited responsiveness over multiple thermal cycles. Here, polymer architecture and TMA content are connected to the aqueous self-assembly, optical response, and thermoreversibility of two distinct types of PNIPAM/TMA copolymers: random P(NIPAM- co -TMA), and a ‘blocky-functionalized’ copolymer where TMA is localized to one portion of the chain, P(NIPAM- b -NIPAM- co -TMA). Aqueous solution behavior characterized via cloud point testing (CPT), dynamic light scattering (DLS), and variable-temperature nuclear magnetic resonance spectroscopy (NMR) demonstrates that thermoresponsiveness and thermoreversibility over multiple cycles is a strong function of polymer configuration and TMA content. Despite low TMA content (≤2 mol%), blocky-functionalized copolymers assemble into small, well-ordered structures above the cloud point that lead to distinct transmittance behaviors and stimuli-responsiveness over multiple cycles. Conversely, random copolymers form disordered aggregates at elevated temperatures, and only exhibit thermoreversibility at negligible TMA fractions (0.5 mol%); higher TMA content leads to irreversible structure formation. This understanding of the architectural and assembly effects on the thermal cyclability of aqueous PNIPAM- co -TMA can be used to improve the scalability of responsive polymer applications requiring thermoreversible behavior, including sensing, separations, and functional coatings. 

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4. Soliton bursts and deterministic dissipative Kerr soliton generation in auxiliary-assisted microcavities

   https://doi.org/10.1038/s41377-019-0161-y  

   Zhou, Heng ; Geng, Yong ; Cui, Wenwen ; Huang, Shu-Wei ; Zhou, Qiang ; Qiu, Kun ; Wei Wong, Chee ( May 2019 , Light: Science & Applications)

   Dissipative Kerr solitons in resonant frequency combs offer a promising route for ultrafast mode-locking, precision spectroscopy and time-frequency standards. The dynamics for the dissipative soliton generation, however, are intrinsically intertwined with thermal nonlinearities, limiting the soliton generation parameter map and statistical success probabilities of the solitary state. Here, via use of an auxiliary laser heating approach to suppress thermal dragging dynamics in dissipative soliton comb formation, we demonstrate stable Kerr soliton singlet formation and soliton bursts. First, we access a new soliton existence range with an inverse-sloped Kerr soliton evolution—diminishing soliton energy with increasing pump detuning. Second, we achieve deterministic transitions from Turing-like comb patterns directly into the dissipative Kerr soliton singlet pulse bypassing the chaotic states. This is achieved by avoiding subcomb overlaps at lower pump power, with near-identical singlet soliton comb generation over twenty instances. Third, with the red-detuned pump entrance route enabled, we uncover unique spontaneous soliton bursts in the direct formation of low-noise optical frequency combs from continuum background noise. The burst dynamics are due to the rapid entry and mutual attraction of the pump laser into the cavity mode, aided by the auxiliary laser and matching well with our numerical simulations. Enabled by the auxiliary-assisted frequency comb dynamics, we demonstrate an application of automatic soliton comb recovery and long-term stabilization against strong external perturbations. Our findings hold potential to expand the parameter space for ultrafast nonlinear dynamics and precision optical frequency comb stabilization.

    

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5. Autoclave Design for Microgravity Hydrothermal Synthesis

   https://doi.org/10.1007/s12217-024-10109-9  

   Frick, Jessica J. ; Ormsby, Rachel ; Li, Zhou ; Ozbakir, Yaprak ; Liu, Chen ; Cox, Jasmine M. ; Carraro, Carlo ; Maboudian, Roya ; Senesky, Debbie G. ( April 2024 , Microgravity Science and Technology)

   Microgravity offers an enticing synthetic knob for materials scientists to explore—however, this environment creates major challenges in hardware development that can turn a simple 3-day experiment into a 3-year long nightmare. This paper provides an overview of engineering an autoclave, compatible with NASA’s Solidification Using a Baffle in Sealed Ampoules (SUBSA) furnace, to enable microgravity hydrothermal synthesis—an acceleration-sensitive technique that processes aqueous samples above the boiling point of water. Hydrothermal synthesis is a universal chemical transformation technique that is used to produce a range of advanced materials with applications in alternative energy, healthcare, and the food industry. In this work, we use the synthesis of graphene hydrogel as a case study to verify our hardware design on Earth before launching to the International Space Station for microgravity testing. The design addresses pertinent challenges which include enabling thermal expansion while preventing air bubble formation in solution and implementing a pressure fail-safe above the maximum operating temperature. Our goal in presenting this autoclave design is to provide a step forward towards commercial-of-the-shelf microgravity hardware.

    

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