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1. Strain tuning of the emission axis of quantum emitters in an atomically thin semiconductor

   https://doi.org/10.1364/OPTICA.377886  

   Chakraborty, Chitraleema; Mukherjee, Arunabh; Moon, Hyowon; Konthasinghe, Kumarasiri; Qiu, Liangyu; Hou, Wenhui; Peña, Tara; Watson, Carla; Wu, Stephen_M; Englund, Dirk; et al (May 2020, Optica)

   Strain engineering is a natural route to control the electronic and optical properties of two-dimensional (2D) materials. Recently, 2D semiconductors have also been demonstrated as an intriguing host of strain-induced quantum-confined emitters with unique valley properties inherited from the host semiconductor. Here, we study the continuous and reversible tuning of the light emitted by such localized emitters in a monolayer tungsten diselenide embedded in a van der Waals heterostructure. Biaxial strain is applied on the emitters via strain transfer from a lead magnesium niobate–lead titanate (PMN-PT) piezoelectric substrate. Efficient modulation of the emission energy of several localized emitters up to 10 meV has been demonstrated on application of a voltage on the piezoelectric substrate. Further, we also find that the emission axis rotates by $\sim <\#comment/>{40}^{\circ <\#comment/>}$as the magnitude of the biaxial strain is varied on these emitters. These results elevate the prospect of using all electrically controlled devices where the property of the localized emitters in a 2D host can be engineered with elastic fields for an integrated opto-electronics and nano-photonics platform. 

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2. Beam Patterning With Directed Surface Acoustic Waves in Extreme Subwavelength Magneto-Elastic Nano-Antennas

   https://doi.org/10.1109/TAP.2024.3521581  

   Fabiha, Raisa; Lundquist, Jonathan; Topsakal, Erdem; Bandyopadhyay, Supriyo (May 2025, IEEE Transactions on Antennas and Propagation)

   Conventional electromagnetic (EM) antennas cannot be aggressively miniaturized since their gain and radiation efficiency plummet when their sizes become much smaller than the radiated wavelength. Recently, we demonstrated a new genre of unconventional extreme subwavelength nano-antennas that are several orders of magnitude smaller than the wavelength they radiate, and yet they radiate efficiently, beating the conventional Harrington limits on the gain and radiation efficiency by many orders of magnitude. This is made possible by their unique unconventional mechanism of activation. These nano-antennas are implemented with 2-D periodic arrays of ∼100-nm-sized nanomagnets deposited on piezoelectric substrates. A surface acoustic wave (SAW) launched in the substrate excites resonant spin waves in the nanomagnets at discrete (GHz) frequencies via phonon–magnon coupling, which radiates EM waves very efficiently at those frequencies via magnon–photon coupling. Normally, one would expect such ultrasmall antennas to behave as point sources that radiate isotropically. Surprisingly, they do not because of the intrinsic anisotropy in the nanomagnet array. The radiation patterns in the plane of the nanomagnets and the two transverse planes are anisotropic. By changing the direction of SAW propagation in the plane of the nanomagnets, one can change the radiation patterns in all three planes, which heralds a new method of beam steering or active electronic scanning. 

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3. Van der Waals Phonon Polariton Microstructures for Configurable Infrared Electromagnetic Field Localizations

   https://doi.org/10.1002/advs.202004872  

   Huang, Wuchao; Sun, Fengsheng; Zheng, Zebo; Folland, Thomas_G; Chen, Xuexian; Liao, Huizhen; Xu, Ningsheng; Caldwell, Joshua_D; Chen, Huanjun; Deng, Shaozhi (May 2021, Advanced Science)

   Abstract Polar van der Waals (vdW) crystals that support phonon polaritons have recently attracted much attention because they can confine infrared and terahertz (THz) light to deeply subwavelength dimensions, allowing for the guiding and manipulation of light at the nanoscale. The practical applications of these crystals in devices rely strongly on deterministic engineering of their spatially localized electromagnetic field distributions, which has remained challenging. The polariton interference can be enhanced and tailored by patterning the vdW crystalα‐MoO₃into microstructures that support highly in‐plane anisotropic phonon polaritons. The orientation of the polaritonic in‐plane isofrequency curve relative to the microstructure edges is a critical parameter governing the polariton interference, rendering the configuration of infrared electromagnetic field localizations by enabling the tuning of the microstructure size and shape and the excitation frequency. Thus, the study presents an effective rationale for engineering infrared light flow in planar photonic devices. 

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4. MYSTIC: a high angular resolution K-band imager at CHARA

   https://doi.org/10.1117/12.2629437  

   Setterholm, Benjamin R.; Monnier, John D.; Le Bouquin, Jean-Baptiste; Anugu, Narsireddy; Ennis, Jacob; Flores, Becky; Gardner, Tyler; Ibrahim, Nour; Jocou, Laurent; Kraus, Stefan; et al (August 2022, SPIE Astronomical Instrumentation)

   Mérand, Antoine; Sallum, Stephanie; Sanchez-Bermudez, Joel (Ed.)

   The Michigan Young STar Imager at CHARA (MYSTIC) is a K-band interferometric beam combining instrument funded by the United States National Science Foundation, designed primarily for imaging sub-au scale disk structures around nearby young stars and to probe the planet formation process. Installed at the CHARA array in July 2021, with baselines up to 331 meters, MYSTIC provides a maximum angular resolution of λ/2B ∼ 0.7 mas. The instrument injects phase corrected light from the array into inexpensive, single-mode, polarization maintaining silica fibers, which are then passed via a vacuum feedthrough into a cryogenic dewar operating at 220 K for imaging. MYSTIC utilizes a high frame rate, ultra-low read noise SAPHIRA detector, and implements two beam combiners: a 6-telescope image plane beam combiner, based on the MIRC-X design, for targets as faint as 7.7 Kmag, as well as a 4-telescope integrated optic beam-combiner mode using a spare chip leftover from the GRAVITY instrument. MYSTIC is co-phased with the MIRC-X (J+H band) instrument for simultaneous fringe-tracking and imaging, and shares its software suite with the latter to allow a single observer to operate both instruments. Herein, we present the instrument design, review its operational performance, present early commissioning science observations, and propose upgrades to the instrument that could improve its K-band sensitivity to 10th magnitude in the near future. 

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5. Long-distance optical pulling of nanoparticle in a low index cavity using a single plane wave

   https://doi.org/10.1126/sciadv.aaz3646  

   Lee, E.; Luo, T. (May 2020, Science Advances)

   Optical pulling force (OPF) can make a nanoparticle (NP) move against the propagation direction of the incident light. Long-distance optical pulling is highly desired for nano-object manipulation, but its realization remains challenging. We propose an NP-in-cavity structure that can be pulled by a single plane wave to travel long distances when the spherical cavity wrapping the NP has a refractive index lower than the medium. An electromagnetic multipole analysis shows that NPs made of many common materials can receive the OPF inside a lower index cavity. Using a silica-Au core-shell NP that is encapsulated by a plasmonic nanobubble, we experimentally demonstrate that a single laser can pull the Au NP-in-nanobubble structure for ~0.1 mm. These results may lead to practical applications that can use the optical pulling of NP, such as optically driven nanostructure assembly and nanoswimmers. 

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