Metasurfaces are composed of periodic pattern of subwavelength structure. They have been of great interest to the scientific community due to their interaction with light in ways that cannot be found in nature. Among various types of metasurfaces, metalenses are ones with promising applications because they can bend and focus light in a confined space. In contrast to conventional refractive lenses, the metalenses are ultra-thin slab with only a few nanometers in thickness suitable for limited space system. However, designing a very thin metalens with requirement of high efficiency is a huge challenge. We designed a high NA metalens with a diameter of less than 25 μm to focus an 830 nm laser beam onto the waveguide situated only a few microns from the laser. The metalens were designed with FDTD simulation and fabricated by distributing Si nanofin structures in a particular pattern using standard electron beam lithography. Determining the efficiency of the metalens itself is a challenge due to small focal spot and background light. Thus, grating of similar physical shape of nano-bricks was used instead for finding efficiency of the metalens. By inspecting diffracted light from metasurface grating, the efficiency of metalens was determined. Here we present the process of designing the metalens, fabrication and testing its efficiency to provide the best solution for limited space optical system.
We studied photoemission of monosaccharides and disaccharides using laser-induced fluorescence spectroscopy. A 532- nm, 10 mW, laser was used to excite the samples and back-scattering signals were collected by a spectrometer. We found that most sugars show weak fluorescence in solid phase but do not fluoresce when dissolved in water solutions. The emission spectra show similar peak intensity at 590 nm, but they are different in emission intensities. We suggest that the fluorescence spectra may be used to differentiate sugar type, even though the origin of the fluorescence is unclear and needed further study.
Optical Tweezers are well known for manipulating and tracking microscopic particles used in many biological and microfluidic applications. Trapping birefringent particles, e.g. liquid crystal droplets, gives insight into the aspect of light polarization in optical tweezers. The outstanding properties of liquid crystal droplets are their high refractive index and birefringent property suitable for light angular momentum transfer. Under the microscope, the Maltese cross of radial nematic liquid crystal droplet was observed. Trapped under 1064 nm Optical Tweezers with power lower than 80 mW, the droplet precession around the focal point of the laser beam was observed due to circular polarization of laser. In this study we show that the precession behavior of radial nematic droplet depends on the degree of ellipticity of polarization state of light, power of the laser source and size of the radial nematic droplet, affecting the induced electrical polarization and internal reordering of the droplets. The theoretical explanation and the model of this behavior have also been determined and discussed.
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