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1. Spatially resolved measurements of ballistic and total transmission in microscale tissue samples from 450 nm to 1624 nm

   https://doi.org/10.1364/BOE.441844  

   Mok, Aaron T. ; Shea, Jamien ; Wu, Chunyan ; Xia, Fei ; Tatarsky, Rose ; Yapici, Nilay ; Xu, Chris ( December 2021 , Biomedical Optics Express)

   We built a simple and versatile setup to measure tissue ballistic and total transmission with customizable wavelength range, spatial resolution, and sample sizes. We performed ballistic transmission and total transmission measurements of overlying structures from biological samplesex vivo. We obtained spatially resolved transmission maps to reveal transmission heterogeneity from five microscale tissue samples:Danionellaskin, mouse skull bone, mosquito cuticle, wasp cuticle, and rat dura over a wide spectral range from 450 nm to 1624 nm at a spatial resolution of ∼25µm for ballistic transmission measurements and ∼50µm for total transmission measurements. We expect our method can be straightforwardly applied to measuring the transmission of other samples. The measurement results will be valuable for multiphoton microscopy. The total transmission of a sample is important for the collection of multiphoton excited fluorescence and the assessment of laser-induced sample heating. The ballistic transmission determines the excitation power at the focus and hence the fluorescence signal generation. Therefore, knowledge of ballistic transmission, total transmission, and transmission heterogeneity of overlying structures of animals and organs are essential to determine the optimal excitation wavelength and fluorophores for non-invasive multiphoton microscopy.

    

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2. The new oxide paradigm for solid state ultraviolet photodetectors

   https://doi.org/10.1117/12.2319505  

   Sandana, Vinod E. ; McClintock, Ryan ; Razeghi, Manijeh ; Harel, Shlomo ; Arrateig, X. ; Rogers, David J. ; Bove, Philippe ; Teherani, Ferechteh H. ; Frisch, Eran ; Teherani, Ferechteh H. ; et al ( March 2018 , Oxide-based Materials and Devices IX)

   The bandgap of wurzite ZnO layers grown on 2 inch diameter c-Al2O3 substrates by pulsed laser deposition was engineered from 3.7 to 4.8 eV by alloying with Mg. Above this Mg content the layers transformed from single phase hcp to mixed hcp/fcc phase before becoming single phase fcc above a bandgap of about 5.5 eV. Metal-Semiconductor-Metal (MSM) photodetectors based on gold Inter-Digitated-Transducer structures were fabricated from the single phase hcp layers by single step negative photolithography and then packaged in TO5 cans. The devices gave over 6 orders of magnitude of separation between dark and light signal with solar rejection ratios (I270 : I350) of over 3 x 105 and dark signals of 300 pA (at a bias of -5V). Spectral responsivities were engineered to fit the “Deutscher Verein des Gas- und Wasserfaches” industry standard form and gave over two decade higher responsivities (14 A/W, peaked at 270 nm) than commercial SiC based devices. Homogeneous Ga2O3 layers were also grown on 2 inch diameter c-Al2O3 substrates by PLD. Optical transmission spectra were coherent with a bandgap that increased from 4.9 to 5.4 eV when film thickness was decreased from 825 to 145 nm. X-ray diffraction revealed that the films were of the β-Ga2O3 (monoclinic) polytype with strong (-201) orientation. β-Ga2O3 MSM photodetectors gave over 4 orders of magnitude of separation between dark and light signal (at -5V bias) with dark currents of 250 pA and spectral responsivities of up to 40 A/W (at -0.75V bias). It was found that the spectral responsivity peak position could be decreased from 250 to 230 nm by reducing film thickness from 825 to 145 nm. This shift in peak responsivity wavelength with film thickness (a) was coherent with the apparent bandgap shift that was observed in transmission spectroscopy for the same layers and (b) conveniently provides a coverage of the spectral region in which MgZnO layers show fcc/hcp phase mixing. 

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3. Low-loss GaO x -core/SiO 2 -cladding planar waveguides on Si substrate

   https://doi.org/10.1364/OE.391036  

   Tan, Si ; Deng, Huiyang ; Urbanek, Karel E. ; Miao, Yu ; Zhao, Zhexin ; Harris, James S. ; Byer, Robert L. ( April 2020 , Optics Express)

   The unique properties of gallium oxide (GaO_x) have drawn increasing interest as a material suitable for high-power electronic and optical applications. Herein, we report the demonstration of low-loss GaO_x-core/SiO₂-cladding waveguides on Si substrate. We present the fabrication process and annealing treatments of the waveguide devices, and we characterize the corresponding effects on optical transmission for 3 common wavelengths: 633 nm, 1064 nm, and 1550 nm. The best propagation loss achieved for these wavelengths is measured to be$-<\#comment/>0.4\pm <\#comment/>0.1\text{dB/cm}$,$-<\#comment/>0.3\pm <\#comment/>0.2\text{dB/cm}$, and$-<\#comment/>2.4\pm <\#comment/>0.5\text{dB/cm}$, respectively. We discuss the major waveguide loss mechanisms, followed by results of pump and probe experiments using visible/IR wavelengths for waveguides treated under various post-fabrication annealing conditions. We also show nonlinear measurements for a 250 fs laser beam to offer additional insights into the loss mechanisms, which are consistent with the linear optical transmission performances. High waveguide laser-induced damage threshold (LIDT) of$>2.5{\text{J/cm}}^2$is measured at this pulse width, making GaO_xa potential candidate for high-power integrated photonic devices.

    

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4. Nonlinear Optical Transmission in WSe2 Induced by Intense THz Fields

   https://doi.org/10.1364/FIO.2022.FTh1C.3  

   Bradley, Alden N. ; Guay, Viela ; Thorp, Spencer G. ; Zhang, Yue ; van der Zande, Arend M. ; Graham, Matthew ; Lee, Yun-Shik ( January 2022 , Optica Publishing Group)

   In WSe2 intense THz fields are found to enhance transmission at 400 nm, while reducing it at 800 nm. The differential transmission is proportional to the field amplitude. The nonlinear responses are fast, yet non-adiabatic.

    

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5. Graphene Oxide-Based Membrane as a Protective Barrier against Toxic Vapors and Gases

   https://doi.org/10.1021/acsami.0c00615  

   Peng, C. ; Iqbal, Z. ; Sirkar, K.K. ; Peterson, G. W. ( February 2020 , ACS applied materials interfaces)

   Traditional protective garments loaded with activated carbons to remove toxic gases are very bulky. Novel graphene oxide (GO) flake-based composite lamellar membrane structure is being developed as a potential component of a garment for protection against chemical warfare agents (CWAs) represented here by simulants, dimethyl methyl phosphonate (DMMP) (a sarin-simulant), and 2-chloroethyl ethyl sulfide (CEES) (a simulant for sulfur mustard), yet allowing a high-moisture transmission rate. GO flakes of dimensions 300−800 nm, 0.7−1.2 nm thickness and dispersed in an aqueous suspension were formed into a membrane by vacuum filtration on a porous poly(ether sulfone) (PES) or poly(ether ether ketone) (PEEK) support membrane for noncovalent π−π interactions with GO flakes. After physical compression of such a membrane, upright cup tests indicated that it can block toluene for 3−4 days and DMMP for 5 days while exhibiting excellent water vapor permeation. Further, they display very low permeances for small-molecule gases/vapors. The GO flakes underwent crosslinking later with ethylenediamine (EDA) introduced during the vacuum filtration followed by physical compression and heating. With a further spray coating of polyurethane (PU), these membranes could be bent without losing barrier properties vis-à-vis the CWA simulant DMMP for 5 days; a membrane not subjected to bending blocked DMMP for 15 days. For the PEEK-EDA-GO-PU compressed membranes after bending, the separation factors of H2O over other species for low gas flow rates in the dynamic moisture permeation cell (DMPC) are: αH2O−He is 42.3; αH2O−N2 is 110; and αH2O−ethane is 1800. At higher gas flow rates in the DMPC, the moisture transmission rate goes up considerably due to reduced boundary layer resistances and exceeds the threshold water vapor flux of 2000 g/(m2·day) that defines a breathable fabric. This membrane displayed considerable resistance to permeation by CEES as well. The PES-EDA-GO-PU-compressed membrane shows good mechanical property under tensile strength tests. 

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