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1. Reducing control noise in gravitational wave detectors with interferometric local damping of suspended optics

   https://doi.org/10.1063/5.0144865  

   van_Dongen, J.; Prokhorov, L.; Cooper, S_J; Barton, M_A; Bonilla, E.; Dooley, K_L; Driggers, J_C; Effler, A.; Holland, N_A; Huddart, A.; et al (May 2023, Review of Scientific Instruments)

   Control noise is a limiting factor in the low-frequency performance of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO). In this paper, we model the effects of using new sensors called Homodyne Quadrature Interferometers (HoQIs) to control the suspension resonances. We show that if we were to use HoQIs, instead of the standard shadow sensors, we could suppress resonance peaks up to tenfold more while simultaneously reducing the noise injected by the damping system. Through a cascade of effects, this will reduce the resonant cross-coupling of the suspensions, allow for improved stability for feed-forward control, and result in improved sensitivity of the detectors in the 10–20 Hz band. This analysis shows that improved local sensors, such as HoQIs, should be used in current and future detectors to improve low-frequency performance. 

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2. Effects of Pressure on Reusable Self-Assembled Microsphere Masks for Microsphere Photolithography

   https://doi.org/10.1115/MSEC2022-85165  

   Zhu, Chen; Kinzel, Edward C. (June 2022, American Society of Mechanical Engineers)

   Microsphere photolithography (MPL) has shown promise for the low-cost large-scale manufacturing of infrared (IR) metasurfaces. One challenge of the technique is that the microsphere array needs to be in immediate proximity to the photoresist because of the near-filed effect of the photonic jet. This is typically accomplished by directly transferring the microsphere array onto the photoresist layer. The microspheres are then washed away during the development of the photoresist. While there may be a possibility of recovering, cleaning, and reusing the microspheres, this is not typically done. This work studies the self-assembly of the microspheres on a superstrate which can be reused as a contact mask. The microspheres are fixed to this superstrate to minimize debonding when they are brought into contact with the substrate. IR metasurfaces are fabricated and spectrally characterized. The resonant wavelength of IR metasurfaces is shown to be a good statistical metric for the variation of the patterned surface. The results indicate pressure between the substrate and superstrate is a critical factor in maintaining a minimum gap between the microspheres and photoresist. This work shows a way forward for mask-based microsphere photolithography and provides guidance for future microlens array-based photolithographic techniques. 

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3. 280-GHz aluminum MKID arrays for the Fred Young Submillimeter Telescope

   https://doi.org/10.1117/1.JATIS.11.2.026005  

   Vaskuri, Anna K; Wheeler, Jordan D; Austermann, Jason E; Vissers, Michael R; Beall, James A; Burgoyne, James; Butler, Victoria; Chapman, Scott; Choi, Steve K; Crites, Abigail; et al (April 2025, Journal of Astronomical Telescopes, Instruments, and Systems)

   First light observations of the 280-GHz instrument module of the Fred Young Submillimeter Telescope in the CCAT Collaboration are expected in 2026. The focal plane of this module will consist of three superconducting microwave kinetic inductance detector (MKID) arrays: two aluminum-based arrays and one titanium nitride array with a similar layout. We have designed, microfabricated, assembled, and characterized a large-format aluminum-based MKID array. The responsivity of the detectors matches design expectation and scales at various optical loading levels as expected for aluminum. We have determined the internal quality factors and optical efficiency of the detectors, feedhorn beam shape, and the detector band pass. The detectors are photon noise limited with the majority of the noise being white photon noise down to 1 Hz. The array matches simulated expectations and is ready for sensitive astronomical observations for CCAT. Certain commercial equipment, instruments, or materials are identified in this paper to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by NIST, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose. 

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4. Multifunctional resonant wavefront-shaping meta-optics based on multilayer and multi-perturbation nonlocal metasurfaces

   https://doi.org/10.1038/s41377-022-00905-6  

   Malek, Stephanie C.; Overvig, Adam C.; Alù, Andrea; Yu, Nanfang (August 2022, Light: Science & Applications)

   Abstract Photonic devices rarely provide both elaborate spatial control and sharp spectral control over an incoming wavefront. In optical metasurfaces, for example, the localized modes of individual meta-units govern the wavefront shape over a broad bandwidth, while nonlocal lattice modes extended over many unit cells support high quality-factor resonances. Here, we experimentally demonstrate nonlocal dielectric metasurfaces in the near-infrared that offer both spatial and spectral control of light, realizing metalenses focusing light exclusively over a narrowband resonance while leaving off-resonant frequencies unaffected. Our devices attain this functionality by supporting a quasi-bound state in the continuum encoded with a spatially varying geometric phase. We leverage this capability to experimentally realize a versatile platform for multispectral wavefront shaping where a stack of metasurfaces, each supporting multiple independently controlled quasi-bound states in the continuum, molds the optical wavefront distinctively at multiple wavelengths and yet stay transparent over the rest of the spectrum. Such a platform is scalable to the visible for applications in augmented reality and transparent displays. 

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5. Miniature High-Coupling Lithium Niobate Thin Film Bulk Acoustic Wave Resonators at 10-30 GHz

   https://doi.org/10.1109/IMS40360.2025.11103794  

   Chulukhadze, Vakhtang; Wang, Yinan; Anderson, Ian; Kramer, Jack; Cho, Sinwoo; Lu, Ruochen (June 2025, IEEE)

   Thin film bulk acoustic wave resonators (FBARs) leveraging sputtered aluminum nitride (AlN) and scandium aluminum nitride (ScAlN) films, are a leading commercial solution for compact radio frequency (RF) filters in mobile devices. However, as 5G/6G bands extend beyond 6 GHz, achieving the required thinner piezoelectric film thicknesses below 500 nm presents a significant challenge to high-quality sputtering, resulting in a moderate quality factor (Q). Additionally, AlN/ScAlN platforms are limited by moderate electromechanical coupling (k2), restricting bandwidth. More recently, ultra-thin transferred single-crystal piezoelectric lithium niobate (LN) has enabled lateral field excited resonators (XBAR) at 10-30 GHz. While these devices boast a high Q and k2, they face challenges with low capacitance density, large footprint, and significant electromagnetic (EM) effects. On the other hand, thickness-field excited LN FBARs face challenges with bottom electrode integration. In this work, we implement a transferred LN on aluminum FBAR platform on sapphire wafers with an intermediate amorphous silicon layer without the need for a patterned bottom electrode. The resonators show first order symmetric mode (S1) at 10.5 GHz with a 3-dB series resonance Q of 38 and k2 of 14.1%, alongside third order symmetric mode (S3) at 27 GHz with a 3-dB series resonance Q of 22 and a high k2 of 11.3%. Further analysis shows that higher Q could be achieved by adjusting the low-loss piezoelectric to lossy metal volume ratio. 

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