More Like this

1. Sub-wavelength lateral detection of tissue-approximating masses using an ultrasonic metamaterial lens

   https://doi.org/10.1038/s41467-020-19591-2  

   Walker, Ezekiel L.; Jin, Yuqi; Reyes, Delfino; Neogi, Arup (December 2020, Nature Communications)

   null (Ed.)

   Abstract Practically applied techniques for ultrasonic biomedical imaging employ delay-and-sum (DAS) beamforming which can resolve two objects down to 2.1 λ within the acoustic Fresnel zone. Here, we demonstrate a phononic metamaterial lens (ML) for detection of laterally subwavelength object features in tissue-like phantoms beyond the phononic crystal evanescent zone and Fresnel zone of the emitter. The ML produces metamaterial collimation that spreads 8x less than the emitting transducer. Utilizing collimation, 3.6x greater lateral resolution beyond the Fresnel zone limit was achieved. Both hard objects and tissue approximating masses were examined in gelatin tissue phantoms near the Fresnel zone limit. Lateral dimensions and separation were resolved down to 0.50 λ for hard objects, with tissue approximating masses slightly higher at 0.73 λ . The work represents the application of a metamaterial for spatial characterization, and subwavelength resolution in a biosystem beyond the Fresnel zone limit. 

   more » « less
2. Diffractive microoptics in porous silicon oxide by grayscale lithography

   https://doi.org/10.1364/OE.538142  

   Siegle, Leander; Xie, Dajie; Richards, Corey A; Braun, Paul V; Giessen, Harald (January 2024, Optics Express)

   We demonstrate focusing as well as imaging using diffractive microoptics, manufactured by two-photon polymerization grayscale lithography (2GL), that have been 3D printed into porous silicon oxide. While typical doublet lens systems require support structures that hold the lenses in place, our optics are held by the porous media itself, decreasing both the fabrication time and design constraints while increasing the optically active area. Compared to the typical two-photon polymerization fabrication process, 2GL offers better shape accuracy while simultaneously increasing throughput. To showcase 2GL manufactured optics in porous media, we fabricate singlet diffractive lenses with a diameter of 500 µm and numerical apertures of up to 0.6. We measure the intensity distribution in the focal plane, and along the optical axis. Furthermore, we design and fabricate a doublet lens system for imaging purposes with a diameter of 600 µm and thinner than 60 µm. We examine the imaging performance with a USAF 1951 resolution test chart and determine the resolution to be 287 lp/mm. 3D printing in porous SiO₂thus holds great promise for future complex and unconventional microoptical solutions. 

   more » « less
3. Negative Index Metamaterial Lens for Subwavelength Microwave Detection

   https://doi.org/10.3390/s21144782  

   Datta, Srijan; Mukherjee, Saptarshi; Shi, Xiaodong; Haq, Mahmood; Deng, Yiming; Udpa, Lalita; Rothwell, Edward (July 2021, Sensors)

   Metamaterials are engineered periodic structures designed to have unique properties not encountered in naturally occurring materials. One such unusual property of metamaterials is the ability to exhibit negative refractive index over a prescribed range of frequencies. A lens made of negative refractive index metamaterials can achieve resolution beyond the diffraction limit. This paper presents the design of a metamaterial lens and its use in far-field microwave imaging for subwavelength defect detection in nondestructive evaluation (NDE). Theoretical formulation and numerical studies of the metamaterial lens design are presented followed by experimental demonstration and characterization of metamaterial behavior. Finally, a microwave homodyne receiver-based system is used in conjunction with the metamaterial lens to develop a far-field microwave NDE sensor system. A subwavelength focal spot of size 0.82λ was obtained. The system is shown to be sensitive to a defect of size 0.17λ × 0.06λ in a Teflon sample. Consecutive positions of the defect with a separation of 0.23λ was resolvable using the proposed system. 

   more » « less
4. Ball Lens‐Assisted Cellphone Imaging with Submicron Resolution

   https://doi.org/10.1002/lpor.202300146  

   Jin, Boya; Jean, Amstrong R; Maslov, Alexey V; Astratov, Vasily N (September 2023, Laser & Photonics Reviews)

   Abstract One of the most significant developments in life sciences—the discovery of bacteria and protists—was accomplished by Antoni van Leeuwenhoek in the 17^thcentury using a single ball lens microscope. It is shown that the full potential of single lens designs can be realized in a contact mode of imaging by ball lenses with a refractive index of n≈ 2, suitable for developing compact cellphone‐based microscopes. The quality of imaging is comparable to basic compound microscopes, but with a narrower field‐of‐view, and is demonstrated for various biomedical samples. The maximal magnification (M > 50) with the highest resolution (≈0.66 µm atλ= 589 nm) is achieved for imaging of nanoplasmonic structures by ball lenses made from LASFN35 glass, the index of which is tuned nearn =2 using chromatic dispersion. Due to limitations of geometrical optics, the imaging theory is developed based on an exact numerical solution of the Maxwell equations, including spherical aberration and the nearfield coupling of a point source. The modeling is performed using multiscale analysis: from the field propagation inside ball lenses with diameters 30 < D/λ < 4000 to the formation of the diffracted field at distances of ≈10⁵λ. It is shown that such imaging enables the transition from pixel‐ to diffraction‐limited resolution in cellphone microscopy. 

   more » « less
5. Large area optimization of meta-lens via data-free machine learning

   https://doi.org/10.1038/s44172-023-00107-x  

   Zhelyeznyakov, Maksym; Fröch, Johannes; Wirth-Singh, Anna; Noh, Jaebum; Rho, Junsuk; Brunton, Steve; Majumdar, Arka (December 2023, Communications Engineering)

   Abstract Sub-wavelength diffractive optics, commonly known as meta-optics, present a complex numerical simulation challenge, due to their multi-scale nature. The behavior of constituent sub-wavelength scatterers, or meta-atoms, needs to be modeled by full-wave electromagnetic simulations, whereas the whole meta-optical system can be modeled using ray/ Fourier optics. Most simulation techniques for large-scale meta-optics rely on the local phase approximation (LPA), where the coupling between dissimilar meta-atoms is neglected. Here we introduce a physics-informed neural network, coupled with the overlapping boundary method, which can efficiently model the meta-optics while still incorporating all of the coupling between meta-atoms. We demonstrate the efficacy of our technique by designing 1mm aperture cylindrical meta-lenses exhibiting higher efficiency than the ones designed under LPA. We experimentally validated the maximum intensity improvement (up to 53%) of the inverse-designed meta-lens. Our reported method can design large aperture ( ~ 10⁴ − 10⁵λ) meta-optics in a reasonable time (approximately 15 minutes on a graphics processing unit) without relying on the LPA. 

   more » « less