Performance of microsphere-assisted imaging in bright-field and dark-field microscopy.

In this work, we study the imaging performance of microsphere-assisted microscopy (MAM) using microspheres with different refractive indices and immersion conditions under both bright-field illumination (BFI) and dark-field illumination (DFI). The experimental results show that the position of the photonic nanojet of the microsphere plays an important role in MAM imaging. The contrast in imaging is affected by the reflection from the microsphere, the background signal without the microsphere, and the electric field on the substrate surface.

Spatial frequency shift super-resolution imaging based on quasiperiodic grating and deep learning.

In this study, we propose a pioneering spatially frequency-shifted super-resolution microscopy technique that utilizes the synergy of quasiperiodic gratings and deep learning. First, a quasiperiodic grating capable of converting evanescent waves into propagating waves is designed. The grating is positioned between the object under investigation and the objective lens, and the high-frequency information carried by the evanescent waves in the near-field region of the object is shifted into the detection window and becomes accessible in the far field for imaging.

Microsphere-assisted dark-field microscopy based on a fully immersed low refractive index microsphere.

Here we find that a fully immersed low refractive index SiO microsphere (or a microcylinder, a yeast cell) can clearly distinguish a sample with sub-diffraction features in dark-field illumination mode. The resolvable area of the sample by microsphere-assisted microscopy (MAM) is composed of two regions. One region locates below the microsphere, and a virtual image of this part of the sample is formed by the microsphere first and then the virtual image is received by the microscope.

Surface plasmon-enhanced dark-field microsphere-assisted microscopy.

We present for the first time a surface plasmon-enhanced dark-field microsphere-assisted microscopy in imaging both low-contrast dielectric objects and metallic ones. We demonstrate, using an Al patch array as the substrate, the resolution and contrast in imaging low-contrast dielectric objects are improved compared to that of the metal plate substrate and a glass slide in dark-field microscopy (DFM). 365-nm-diameter hexagonally arranged SiO nanodots assembled on the three substrates can be resolved, with the contrast varied from 0.

Super-resolution imaging of plasmonic nanostructures by microsphere-assisted microscopy.

We fabricate both triangularly and circularly shaped Au, Ag, and Cr nanoparticle arrays and observe the imaging properties of these plasmonic nanostructures by glass (BTG) microsphere-assisted microscopy. We experimentally find that the resolution of triangularly shaped Ag nanoparticle arrays is higher than that of Au and Cr ones, and a gap resolution of ∼/7.7 is demonstrated for the circularly shaped Au, Ag, and Cr nanostructures.

Direct observation Brownian motion of individual nanoparticles in water using microsphere-assisted microscopy.

Observing Brownian motion of nanoscale objects through a traditional optical microscope is still a challenge. Here, we present a method to overcome this challenge by using a traditional optical microscope assisted with a removable microsphere-embedded thin film. The diffusion coefficient of individual unconstrained polystyrene (PS) nanoparticles with a diameter of 300 nm in water is calculated from their respective mean-square displacement versus time curves, and the measured diffusion coefficient shows good agreement with the theoretical Stokes-Einstein one, proving the feasibility of our method.

A Multilayer Emitter Close to Ideal Solar Reflectance for Efficient Daytime Radiative Cooling.

A passive radiative cooling method has a significant influence on thermal management applications because it can cool without any energy input. This work both experimentally and theoretically demonstrates a multilayer thin film structure with high solar reflectance, which can be applied to passive daytime radiative cooling. The combination of physical vapor deposition and spin-coating prepared the samples, which were also characterized experimentally by spectrometers.

Reduced distortion in high-index microsphere imaging by partial immersion.

We experimentally demonstrate that pincushion distortion is obvious when using a BaTiO glass (BTG) microsphere fully immersed in ethanol or SU-8 2002 resist to image a Blu-ray disk with sub-diffraction features. The distortion is related to the layer thickness of the immersing medium. For a BTG microsphere partially immersed in the SU-8 resist where the SU-8 thickness is around 4/5 the diameter of the microsphere, its distortion decreases dramatically, but it can still clearly resolve the Blu-ray disk.

Super-resolution imaging properties of cascaded microsphere lenses.

In this paper, the imaging properties of a cascaded microsphere lens are studied. The cascaded microsphere lens consists of two lenses. A hexagonally close-packed 960-nm-diameter array of polystyrene microspheres is used as the first lens.

Influence of the photonic nanojet of microspheres on microsphere imaging.

The imaging properties of BaTiO glass (BTG) microspheres in the diameter range of 5-50 µm which are fully immersed in a polydimethylsiloxane layer are experimentally studied. Our experimental results show that for both Blu-ray disc samples and the single-layer hexagonally close-packed microsphere array samples, with the increase of the diameter of BTG microspheres, the range of focal image positions (RFIP) increases linearly. When the diameter of BTG microspheres increases from 5 to 50 μm, the RFIP changes from 4 to 25 μm.

Experimental imaging properties of immersion microscale spherical lenses.

Using the immersion lensing technique, the resolution of a conventional spherical lens can be improved by a factor of 1/n over its value in air (n, the refractive index of the immersion medium). Depending on the relative position between an object and a lens, either a real or a virtual image is formed. Here we report a new physical phenomenon experimentally observed in the microscale lens imaging.

Mimicking bicolor by changing the reflectance of the substrate in a one-dimensional periodic structure.

In nature, some beetles can display bicolor on their elytra. In order to explore the bicolor mechanism, we experimentally studied the optical and structural properties of the Carabus lafossei beetle. We found a multilayer structure in the cuticle of the beetle.

Experimental far-field imaging properties of a ~5-μm diameter spherical lens.

Microscale lenses are mostly used as near-sighted lenses. The far-field imaging properties of a microscale spherical lens, where the lens is spatially separated from the object, are experimentally studied. Our experimental results show that, for a blu-ray disc (an object) whose spacing is 300 nm, the lens can magnify the stripe patterns of the disc when the lens is spatially separated from the object.

Gravity-assisted convective assembly of centimeter-sized uniform two-dimensional colloidal crystals.

We have developed an inexpensive, robust, and easily controlled method, a gravity-assisted convective self-assembly method, to fabricate centimeter-sized uniform two-dimensional colloidal crystals. In this method, centimeter-sized two-dimensional colloidal crystals can be formed when the suspension concentration is in the range of 0.32-2.

Tunable figure of merit for a negative-index metamaterial with a sandwich configuration.

Metamaterials with a free-standing Ag-SU-8-Ag sandwich configuration, perforated with a periodic array of cross-dipole apertures, are fabricated. The transmittance spectra of both experiment and simulation have indicated the existence of two transmission bands in mid-IR frequencies. The high-frequency transmission peak is the guided mode associated with the surface plasmon polariton (SPP), and its location strongly depends on the arm length of the cross-dipole.

Role of shape in middle-infrared transmission enhancement through periodically perforated metal films.

We report experimental results on the role of aperture shape in middle-infrared enhanced transmission through a metal film perforated with a periodic aperture array. The transmission spectrum is highly dependent on the aperture shape. When the aperture shape changes from circular to cross-dipole or the cross-dipole arm length increases, the transmission spectrum exhibits a large redshift.

Enhanced light transmission through cascaded metal films perforated with periodic hole arrays.

We report experimental results on enhanced light transmission through two periodically perforated metal films separated by a layer of dielectric. A perforated metal film (single metallic structure) exhibits extraordinary optical transmission, and when two such perforated metal films are spaced by a dielectric layer (cascaded metallic structure), the transmission is further increased. The maximum transmission of the cascaded metallic structure, which depends on the distance between the two metal films, can be more than 400% greater than that of a corresponding single metallic structure.

Finite-size effect on one-dimensional coupled-resonator optical waveguides.

We study the finite-size effect on the dispersion relation, group velocity, and transmission curves of one-dimensional finite-size coupled-resonator optical waveguide (CROW) structures. Both the dispersion relation and the group velocity curves of a finite-size CROW oscillate along those of the corresponding infinite-extended ones. The oscillations can be suppressed by matching the equivalent admittance of the surrounding medium to that of the unit cell.

Modified spontaneous emission of CdTe quantum dots inside a photonic crystal.

The angular dependence of the spontaneous emission of CdTe quantum dots (QDs) inside a photonic crystal with a pseudogap is reported. The sensitive dependences of the radiative lifetime and the photoluminescence spectrum of CdTe QDs on the observation angle demonstrate the effect of the photonic bandgap on the spontaneous emission of the QDs.

[Factors affecting the determination of the percent carboxyhemoglobin saturation of blood].

Objective: To investigate factors affecting the determination of the percent carboxyhemoglobin saturation (HbCO%) of blood in an attempt to offer further data for results interpretation and sample storage requirement.

Methods: The HbCO% of blood samples stored in various conditions were detected by three spectrophotometries during the succeeding 30 days.

Results: The data detected by reductive double-wavelength spectrophotometry and double-wavelength spectrophotometry were more stable than mono-wavelength spectrophotometry.