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1. Hyperspectral Raman Imaging Using a Spatial Heterodyne Raman Spectrometer with a Microlens Array

   https://doi.org/10.1177/0003702820906222  

   Allen, Ashley; Waldron, Abigail; Ottaway, Joshua M.; Chance Carter, J.; Michael Angel, S. (August 2020, Applied Spectroscopy)

   null (Ed.)

   A new hyperspectral Raman imaging technique is described using a spatial heterodyne Raman spectrometer (SHRS) and a microlens array (MLA). The new technique enables the simultaneous acquisition of Raman spectra over a wide spectral range at spatially isolated locations within two spatial dimensions ( x, y) using a single exposure on a charge-coupled device (CCD) or other detector types such as a complementary metal-oxide semiconductor (CMOS) detector. In the SHRS system described here, a 4 × 4 mm MLA with 1600, 100 µm diameter lenslets is used to image the sample, with each lenslet illuminating a different region of the SHRS diffraction gratings and forming independent fringe images on the CCD. The fringe images from each lenslet contain the fully encoded Raman spectrum of the region of the sample “seen” by the lenslet. Since the SHRS requires no moving parts, all fringe images can be measured simultaneously with a single detector exposure, and in principle using a single laser shot, in the case of a pulsed laser. In this proof of concept paper, hyperspectral Raman spectra of a wide variety of heterogeneous samples are used to characterize the technique in terms of spatial and spectral resolution tradeoffs. It is shown that the spatial resolution is a function of the diameter of the MLA lenslets, while the number of spatial elements that can be resolved is equal to the number of MLA lenslets that can be imaged onto the SHRS detector. The spectral resolution depends on the spatial resolution desired, and the number of grooves illuminated on both diffraction gratings by each lenslet, or combination of lenslets in cases where they are grouped. 

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2. Experimental investigation on nanowire array irradiated with ultrahigh intensity laser at x-ray free electron laser facility SACLA: Fabrication of nanowire array target and its application to ultrafast time-resolved measurements

   https://doi.org/10.1063/5.0251649  

   Tanaka, D.; Sawada, H.; Idesaka, T.; Nakatsuji, C.; Matsuura, S.; Sato, T.; Somekawa, T.; Yabuuchi, T.; Miyanishi, K.; Sueda, K.; et al (March 2025, Journal of Applied Physics)

   Nanowire arrays—vertically aligned metal wires with a few hundred nanometers in diameter—are promising nano-structured targets for high-energy-density physics and related applications. We have been developing ultrafast, time-resolved measurements on laser-irradiated targets using the x-ray free electron laser at the SACLA facility. Here, we present fabrication of various kinds of nanowire array in order to explore the absorption mechanism with ultrahigh intensity laser irradiation, and their application to the laser-irradiation experiment is performed at the SACLA facility. To fabricate nanowire arrays with control over their spatial and material parameters, we have developed an approach using an anodic aluminum oxide template and electroplating processes. The nanowire array samples were applied for ultrahigh intensity laser experiments, which coupled with x-ray free-electron-laser facility SACLA. We characterized fundamental “static” data on transmittance calibration for x-ray shadowgraph measurements. We also evaluated the effect of a pre-pulse on spatial changes of a nanowire, showing that the shape of the nanowires was maintained up to a few picoseconds after laser irradiation. On the preliminary laser-irradiation experiments, we observed time-resolved, two-dimensional x-ray images and observed the x-ray transmittance change due to the heating process. 

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3. Experimental Studies on Fabricating Lenslet Array with Slow Tool Servo

   https://doi.org/10.3390/mi13101564  

   Kang, Wenjun; Seigo, Masafumi; Xiao, Huapan; Wang, Daodang; Liang, Rongguang (October 2022, Micromachines)

   On the demand of low-cost, lightweight, miniaturized, and integrated optical systems, precision lenslet arrays are widely used. Diamond turning is often used to fabricate lenslet arrays directly or molds that are used to mold lenslet arrays. In this paper, mainly by real-time monitoring position following error for slow tool servo, different fabrication parameters are quantitatively studied and optimized for actual fabrication, then by actual fabrication validation, uniform and high-fidelity surface topography across the actual whole lenslet array is achieved. The evaluated fabrication parameters include sampling strategy, inverse time feed, arc-length, etc. The study provides a quick, effective, and detailed reference for both convex and concave lenslet array cutting parameter selection. At the end, a smooth zonal machining strategy toolpath is demonstrated for fabricating concave lenslet arrays. 

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4. Thermal noise and mechanical loss of SiO ₂ /Ta ₂ O ₅ optical coatings at cryogenic temperatures

   https://doi.org/10.1364/OL.413758  

   Robinson, John_M; Oelker, Eric; Milner, William_R; Kedar, Dhruv; Zhang, Wei; Legero, Thomas; Matei, Dan_G; Häfner, Sebastian; Riehle, Fritz; Sterr, Uwe; et al (January 2021, Optics Letters)

   Mechanical loss of dielectric mirror coatings sets fundamental limits for both gravitational wave detectors and cavity-stabilized optical local oscillators for atomic clocks. Two approaches are used to determine the mechanical loss: ringdown measurements of the coating quality factor and direct measurement of the coating thermal noise. Here we report a systematic study of the mirror thermal noise at 4, 16, 124, and 300 K by operating reference cavities at these temperatures. The directly measured thermal noise is used to extract the mechanical loss for ${\mathrm{S}\mathrm{i}\mathrm{O}}_2/{\mathrm{T}\mathrm{a}}_2{\mathrm{O}}_5$coatings, which are compared with previously reported values. 

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5. Characterization of an angular domain fluorescence optical projection tomography system for mesoscopic lymph node imaging

   https://doi.org/10.1364/AO.411577  

   Torres, Veronica_C; Li, Chengyue; Zhou, Wei; Brankov, Jovan_G; Tichauer, Kenneth_M (December 2020, Applied Optics)

   Transmittance and fluorescence optical projection tomography can offer high-resolution and high-contrast visualization of whole biological specimens; however, applications are limited to samples exhibiting minimal light scattering. Our previous work demonstrated that angular-domain techniques permitted imaging of $\sim <\#comment/>1\mathrm{c}\mathrm{m}$diameter noncleared lymph nodes because of their low scattering nature. Here, an angle-restricted transmittance/fluorescence system is presented and characterized in terms of geometric and fluorescence concentration reconstruction accuracy as well as spatial resolution, depth of focus, and fluorescence limits of detection. Using lymph node mimicking phantoms, results demonstrated promising detection and localization capabilities relevant for clinical lymph node applications. 

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