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1. Diel variability of bulk optical properties associated with the growth and division of small phytoplankton in the North Pacific Subtropical Gyre

   https://doi.org/10.1364/AO.394123  

   Henderikx_Freitas, Fernanda; Dugenne, Mathilde; Ribalet, François; Hynes, Annette; Barone, Benedetto; Karl, David_M; White, Angelicque_E (July 2020, Applied Optics)

   Cross-platform observing systems are requisite to capturing the temporal and spatial dynamics of particles in the ocean. We present simultaneous observations of bulk optical properties, including the particulate beam attenuation ( ${\text{c}}_{\text{p}}$) and backscattering ( $b_{\text{bp}}$) coefficients, and particle size distributions collected in the North Pacific Subtropical Gyre. Clear and coherent diel cycles are observed in all bulk and size-fractionated optical proxies for particle biomass. We show evidence linking diurnal increases in ${\text{c}}_{\text{p}}$and ${\text{b}}_{\text{bp}}$to daytime particle growth and division of cells, with particles $<<\#comment/>7\text{µ<\#comment/>}\mathrm{m}$driving the daily cycle of particle production and loss within the mixed layer. Flow cytometry data reveal the nitrogen-fixing cyanobacteriumCrocosphaera( $\sim <\#comment/>4-<\#comment/>7\text{µ<\#comment/>}\mathrm{m}$) to be an important driver of ${\text{c}}_{\text{p}}$at the time of sampling, whereasProchlorococcusdynamics ( $\sim <\#comment/>0.5\text{µ<\#comment/>}\mathrm{m}$) were essential to reproducing temporal variability in ${\text{b}}_{\text{bp}}$. This study is a step towards improved characterization of the particle size range represented byin situbulk optical properties and a better understanding of the mechanisms that drive variability in particle production in the oligotrophic open ocean. 

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2. Mid-IR spectroscopy of Er ³⁺ doped low-phonon CsCdCl ₃ and CsPbCl ₃ crystals

   https://doi.org/10.1364/JOSAB.470152  

   Brown, Ei_Ei; Fleischman, Zackery_D; McKay, Jason; Hommerich, Uwe; Kabir, Al_Amin; Riggins, Jazmine; Trivedi, Sudhir; Dubinskii, Mark (September 2022, Journal of the Optical Society of America B)

   The mid-IR spectroscopic properties of ${\mathrm{E}\mathrm{r}}^{3+}$doped low-phonon ${\mathrm{C}\mathrm{s}\mathrm{C}\mathrm{d}\mathrm{C}\mathrm{l}}_3$and ${\mathrm{C}\mathrm{s}\mathrm{P}\mathrm{b}\mathrm{C}\mathrm{l}}_3$crystals grown by the Bridgman technique have been investigated. Using optical excitations at $\sim <\#comment/>800\mathrm{n}\mathrm{m}$and $\sim <\#comment/>660\mathrm{n}\mathrm{m}$, both crystals exhibited IR emissions at $\sim <\#comment/>1.55$, $\sim <\#comment/>2.75$, $\sim <\#comment/>3.5$, and $\sim <\#comment/>4.5\text{µ<\#comment/>}\mathrm{m}$at room temperature. The mid-IR emission at 4.5 µm, originating from the ${}^4{\mathrm{I}}_{9/2}\to <\#comment/>{}^4{\mathrm{I}}_{11/2}$transition, showed a long emission lifetime of $\sim <\#comment/>11.6\mathrm{m}\mathrm{s}$for ${\mathrm{E}\mathrm{r}}^{3+}$doped ${\mathrm{C}\mathrm{s}\mathrm{C}\mathrm{d}\mathrm{C}\mathrm{l}}_3$, whereas ${\mathrm{E}\mathrm{r}}^{3+}$doped ${\mathrm{C}\mathrm{s}\mathrm{P}\mathrm{b}\mathrm{C}\mathrm{l}}_3$exhibited a shorter lifetime of $\sim <\#comment/>1.8\mathrm{m}\mathrm{s}$. The measured emission lifetimes of the ${}^4{\mathrm{I}}_{9/2}$state were nearly independent of the temperature, indicating a negligibly small nonradiative decay rate through multiphonon relaxation, as predicted by the energy-gap law for low-maximum-phonon energy hosts. The room temperature stimulated emission cross sections for the ${}^4{\mathrm{I}}_{9/2}\to <\#comment/>{}^4{\mathrm{I}}_{11/2}$transition in ${\mathrm{E}\mathrm{r}}^{3+}$doped ${\mathrm{C}\mathrm{s}\mathrm{C}\mathrm{d}\mathrm{C}\mathrm{l}}_3$and ${\mathrm{C}\mathrm{s}\mathrm{P}\mathrm{b}\mathrm{C}\mathrm{l}}_3$were determined to be $\sim <\#comment/>0.14\times <\#comment/>{10}^{-<\#comment/>20}{\mathrm{c}\mathrm{m}}^2$and $\sim <\#comment/>0.41\times <\#comment/>{10}^{-<\#comment/>20}{\mathrm{c}\mathrm{m}}^2$, respectively. The results of Judd–Ofelt analysis are presented and discussed. 

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3. Optomechanical inertial sensors

   https://doi.org/10.1364/AO.393061  

   Hines, Adam; Richardson, Logan; Wisniewski, Hayden; Guzman, Felipe (June 2020, Applied Optics)

   We present a performance analysis of compact monolithic optomechanical inertial sensors that describes their key fundamental limits and overall acceleration noise floor. Performance simulations for low-frequency gravity-sensitive inertial sensors show attainable acceleration noise floors on the order of $1\times <\#comment/>{10}^{-<\#comment/>11}\mathrm{m}/{\mathrm{s}}^2\sqrt{\mathrm{H}\mathrm{z}}$. Furthermore, from our performance models, we devised an optimization approach for our sensor designs, sensitivity, and bandwidth trade space. We conducted characterization measurements of these compact mechanical resonators, demonstrating $\text{mQ}$-products at levels of 250 kg, which highlight their exquisite acceleration sensitivity. 

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4. Monolithic all-silicon flat lens for broadband LWIR imaging

   https://doi.org/10.1364/OL.426384  

   Kigner, Orrin; Meem, Monjurul; Baker, Brian; Banerji, Sourangsu; Hon, Philip_W_C; Sensale-Rodriguez, Berardi; Menon, Rajesh (August 2021, Optics Letters)

   We designed, fabricated, and characterized a flat multi-level diffractive lens comprised of only silicon with $\mathrm{d}\mathrm{i}\mathrm{a}\mathrm{m}\mathrm{e}\mathrm{t}\mathrm{e}\mathrm{r}=15.2\mathrm{m}\mathrm{m}$, focal $\mathrm{l}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{t}\mathrm{h}=19\mathrm{m}\mathrm{m}$, numerical aperture of 0.371, and operating over the long-wave infrared (LWIR) $\mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{r}\mathrm{u}\mathrm{m}=8\text{µ<\#comment/>}\mathrm{m}$to 14 µm. We experimentally demonstrated a field of view of 46°, depth of focus $><\#comment/>5\mathrm{m}\mathrm{m}$, and wavelength-averaged Strehl ratio of 0.46. All of these metrics were comparable to those of a conventional refractive lens. The active device thickness is only 8 µm, and its weight (including the silicon substrate) is less than 0.2 g. 

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5. Universal parameter to describe the reduction of refraction effects in the scattering of absorbing spheres

   https://doi.org/10.1364/JOSAA.394401  

   Maughan, Justin_B; Sorensen, Christopher_M (August 2020, Journal of the Optical Society of America A)

   The scattered intensity from large spheres with a real part of the refractive index of $n=1.33,1.5,2.0$is investigated as the radius $R$and an imaginary part of the refractive index $\mathrm{\kappa <\#comment/>}$are varied. It is shown that the product of $\mathrm{\kappa <\#comment/>}$and the size parameter $kR$, $\mathrm{\kappa <\#comment/>}\text{kR}$, is a universal parameter describing the quenching of the refraction phenomenon of the scattered light: the refraction hump, the generalized rainbows, and the glory. The physical reason for this is that $\mathrm{\kappa <\#comment/>}\text{kR}$is the inverse of the relative skin depth of light penetration into the sphere, which is demonstrated by calculations of the internal fields that darken universally as $\mathrm{\kappa <\#comment/>}\text{kR}$increases. 

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