More Like this

1. Improved Femtosecond 3D Light Field Lithography With a Phase-Controlled Spatial Light Modulator

   https://doi.org/10.1115/HT2022-85681  

   Jakkinapalli, Aravind; Wen, Sy-Bor (September 2022, ASME SHTC 2022)

   Abstract Through years of development, we have successfully demonstrated 3D light field lithography with UV continuous light. We recently combined this approach with femtosecond laser sources as two-photon femtosecond 3D light lithography. It is found that consistent results can happen under limited conditions with this direct combination. Our theoretical analysis reported last year shows that the experimental difficulty can be attributed to digital micro-mirror devices (DMD) and microlens arrays (MLA) used in the current 3D light field projection. Though they can control the propagation directions and interact at designed 3D locations, rays from such a system diverge with respect to the propagation distance. As a result, 3D voxel intensity in the 3D projection changes as a function of the separation distance with respect to the MLA in the 3D projection. To solve this problem, we replace the combination of DMD and MLA with a phase-controlled spatial light modulator. With a lab-developed algorithm, a single femtosecond laser pulse can generate up to a million sub-rays through the phase-controlled spatial light modulator. These sub-rays with a precisely controlled propagation direction can intersect at designed 3D locations as voxels for 3D virtual object constructions. Moreover, these sub-rays have minimum divergence angles to ensure that the voxel intensities are maintained consistently at each 3D location. We also demonstrated that versatile 3D patterns could be generated with two-photon femtosecond 3D light field lithography based on this innovative approach. 

   more » « less
2. KMT-2021-BLG-0322: Severe degeneracy between triple-lens and higher-order binary-lens interpretations

   https://doi.org/10.1051/0004-6361/202141939  

   Han, Cheongho; Gould, Andrew; Hirao, Yuki; Lee, Chung-Uk; Albrow, Michael D.; Chung, Sun-Ju; Hwang, Kyu-Ha; Jung, Youn Kil; Kim, Doeon; Mao, Shude; et al (November 2021, Astronomy & Astrophysics)

   Aims. We investigate the microlensing event KMT-2021-BLG-0322, for which the light curve exhibits three distinctive sets of caustic-crossing features. It is found that the overall features of the light curve are approximately described by a binary-lens (2L1S) model, but the model leaves substantial residuals. We test various interpretations with the aim of explaining the residuals. Methods. We find that the residuals can be explained either by considering a nonrectilinear lens-source motion caused by the microlens-parallax and lens-orbital effects or by adding a low-mass companion to the binary lens (3L1S model). The degeneracy between the higher-order 2L1S model and the 3L1S model is very severe, making it difficult to single out a correct solution based on the photometric data. This degeneracy was known before for two previous events (MACHO-97-BLG-41 and OGLE-2013-BLG-0723), which led to the false detections of planets in binary systems, and thus the identification of the degeneracy for KMT-2021-BLG-0322 illustrates that the degeneracy can be not only common but also very severe, emphasizing the need to check both interpretations of deviations from 2L1S models. Results. From the Bayesian analysis conducted with the measured lensing observables of the event timescale, angular Einstein radius, and microlens parallax, it was estimated that the binary lens components have masses ( M 1 , M 2 ) = (0.62 −0.26 +0.25   M ⊙ , 0.07 −0.03 +0.03   M ⊙ ), for both 2L1S and 3L1S solutions, and the mass of the tertiary lens component according to the 3L1S solution is M 3  = 6.40 −2.78 +2.64   M J . 

   more » « less
3. Toward implantable devices for angle-sensitive, lens-less, multifluorescent, single-photon lifetime imaging in the brain using Fabry–Perot and absorptive color filters

   https://doi.org/10.1038/s41377-022-00708-9  

   Taal, Adriaan J.; Lee, Changhyuk; Choi, Jaebin; Hellenkamp, Björn; Shepard, Kenneth L. (December 2022, Light: Science & Applications)

   Abstract Implantable image sensors have the potential to revolutionize neuroscience. Due to their small form factor requirements; however, conventional filters and optics cannot be implemented. These limitations obstruct high-resolution imaging of large neural densities. Recent advances in angle-sensitive image sensors and single-photon avalanche diodes have provided a path toward ultrathin lens-less fluorescence imaging, enabling plenoptic sensing by extending sensing capabilities to include photon arrival time and incident angle, thereby providing the opportunity for separability of fluorescence point sources within the context of light-field microscopy (LFM). However, the addition of spectral sensitivity to angle-sensitive LFM reduces imager resolution because each wavelength requires a separate pixel subset. Here, we present a 1024-pixel, 50  µm thick implantable shank-based neural imager with color-filter-grating-based angle-sensitive pixels. This angular-spectral sensitive front end combines a metal–insulator–metal (MIM) Fabry–Perot color filter and diffractive optics to produce the measurement of orthogonal light-field information from two distinct colors within a single photodetector. The result is the ability to add independent color sensing to LFM while doubling the effective pixel density. The implantable imager combines angular-spectral and temporal information to demix and localize multispectral fluorescent targets. In this initial prototype, this is demonstrated with 45 μm diameter fluorescently labeled beads in scattering medium. Fluorescent lifetime imaging is exploited to further aid source separation, in addition to detecting pH through lifetime changes in fluorescent dyes. While these initial fluorescent targets are considerably brighter than fluorescently labeled neurons, further improvements will allow the application of these techniques to in-vivo multifluorescent structural and functional neural imaging. 

   more » « less
4. 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. 

   more » « less
5. Microlens Coupler from Integrated Photonic Circuit to Fiber Design for Space Application

   Xu, Chengtao; Shivakumar, Jayaprakash B.; Rojas-Nastrucci, Eduardo (January 2024, IEEE Space Hardware and Radio Conference)

   This study presents a novel design for a microlens coupler to transfer light from a straight waveguide to a single-mode fiber (SMF). Our design combines improved mode matching and enhanced alignment tolerance compared to edge coupling. An investigation of the alignment tolerance is done by assessing coupling efficiency under various degrees of manufacturing-induced misalignment. Singlet and diffractive lenses are incorporated into our design to focus the light into the fiber precisely. Comprehensive simulations demonstrate that the diffractive lens outperforms edge coupling and singlet lens in coupling efficiency. Fabrication methods such as additive manufacturing are discussed for future works. Our findings underscore the potential of innovative microlens coupler design. 

   more » « less