4x4 Element Research Articles

Multispectral Stokes/Mueller Detection Module for Multiphoton/Fluorescence Confocal Scanning Imaging Microscopy

Mueller-matrix microscopy as proved to be an important tool to extract the full optical properties of a sample, without labelling or a priori knowledge of the sample. It consists in studying the interaction between the polarized light and the medium, which can be summarized in a single 4x4 elements Mueller-matrix. In this way, this method gives access to physical parameters such as dichroism, birefringence and scattering, from the macro- to the microscopic scale. More particularly, it has been proven its efficiency for quantitative methods for materials science and biomedical diagnosis.

Stokes-vector Resolved Multiphoton/Fluorescence Confocal Scanning Microscopy

Microscopy techniques based on the measurements of polarimetric contrasts as proved to be an important tool to extract additional information about the organization and orientation of any anisotropic sample. More particularly, it has been proven their efficiency for quantitative methods for materials science and biomedical diagnosis. Among these techniques, we have developed a complete Stokes-vector and Mueller-matrix scanning microscope allowing the acquisition of all the physical effects induced by the interaction of the polarized light with a medium. This interaction can be summarized in a single 4x4 elements Mueller-matrix by comparing the independent coding and decoding polarization states, giving access to physical parameters such as dichroism, birefringence, and scattering, from the macro- to the microscopic scale. In this work, we proposed to image the anisotropic emission of molecules under illumination from multiphoton and fluorescence microscopy available on the same scanning microscope. Using Stokes-Mueller formalism, we demonstrate the potentiality to acquire intensity images combined with the anisotropy factor orientation and the scattering (Degree of Polarization) mapping for both modalities. As proof of principle, we have imaged particular biological structures of interests (collagen fibers and muscles) for thin and thick samples. Combining all this information, we propose to quantify locally the cellular and molecular organization at a different scale, from the microscopic to the nanoscopic level.

Modeling of Chromatin DNA by Polarized Light Scattering

Polarized light scattering based techniques are non-invasive and label-free approaches allowing the description of physical parameters, such as size and molecular orientation of any kind of sample. More particularly, Mueller matrix polarimetry is a 4x4 elements mathematical tool which quantitatively describes the properties of sample from the measurements of scattered polarized light, such as the birefringence dichroism and scattering. The circular intensity differential scattering, S14 element of Mueller matrix, has been particularly reported to describe chiral properties of chromatin DNA. Recently, an experiment has been designed to measure the polarized light scattering images. In this way, we have acquired the absorption and scattering spectra of chromatin DNA organization at the single cellular level using polarized light scattering imaging, in the form of a Fourier (θ, φ) images. The topic of this presentation is to compare the acquired images with simulated ones from the Mie theory and the discrete dipole approximation (DDA). As a proof of principle of the calculation, simulations of scattering images of microspheres size were performed which demonstrated the correlation with the experimental results verifies the working of the technique. In a second step, DDA simulated images, combined with the experimental measurements of different population of cells demonstrate this technique as an interesting method to quantify biopolymers organization to micro- to nanoscopic scale.

Design of a Dielectric Rod Waveguide Antenna Array for Millimeter Waves

In this manuscript, the use of dielectric rod waveguide (DRW) antennas in the millimeter and sub-millimeter wave range is presented as a solution for covering two issues: getting more radiated power and filling a technological gap problem in the terahertz band, namely a fully electronic beam steering. A 4x4 element array working at 100 GHz fed by a rectangular waveguide is manufactured and measured for showing its capabilities. This topology can be used as a cost-affordable alternative to dielectric lenses in photomixer-based terahertz sources.

Evaluation of a SiPM array detector coupled to a LFS-3 pixellated scintillator for PET/MR applications.

SiPM arrays are insensitive to magnetic fields and thus good candidates for hybrid PET/MR imaging systems. Moreover, due to their small size and flexibility can be used in dedicated small field of view small animal imaging detectors and especially in head PET/MR studies in mice. Co-doped LFS-3 scintillator crystals have higher light yield and slightly faster response than that of LSO:Ce mainly due to the co-doped activation of emission centers with varying materials such as Ce, Gd, Sc, Y, La, Tb, or Ca distributed at the molecular scale through the lutetium silicate crystal host. The purpose of this study is to investigate the behavior of the SensL ArraySL-4 (4x4 element array of 3x3 mm2 silicon photomultipliers) optical detector coupled to a 6x6 LFS-3 scintillator array, with 2x2x5 mm3 crystal size elements, for possible applications in small field of view PET/MR imaging detectors. We have designed a symmetric resistive charge division circuit to read out the signal outputs of 4x4 pixel SiPM array reducing the 16 pixel outputs of the photodetector to 4 position signals. The 4 position signals were digitized using free running Analog to Digital Converters. The ADCs sampling rate was 50 MHz. An FPGA (Spartan 6 LX150T) was used for triggering and digital signal processing of the pulses. Experimental evaluation was carried out with 22Na radioactive source and the parameters studied where energy resolution and peak to valley ratio. The first preliminary results of the evaluation shows a clear visualization of the discrete 2x2x5 mm3 LFS-3 scintillator elements. The mean peak to valley ratio of the horizontal profiles on the raw image was measured equal to 11 while the energy resolution was calculated equal to 30% at the central pixels.

2<formula formulatype="inline"><tex Notation="TeX">$\times$</tex> </formula>2-Slot Element for 60-GHz Planar Array Antenna Realized on Two Doubled-Sided PCBs Using SIW Cavity and EBG-Type Soft Surface fed by Microstrip-Ridge Gap Waveguide

A wideband 2x2-slot element for a 60-GHz antenna array is designed by making use of two double-sided printed circuit boards (PCBs). The upper PCB contains the four radiating cavity-backed slots, where the cavity is formed in substrate-integrated waveguide (SIW) using metalized via holes. The SIW cavity is excited by a coupling slot. The excitation slot is fed by a microstrip-ridge gap waveguide formed in the air gap between the upper and lower PCBs. The lower PCB contains the microstrip line, being short-circuited to the ground plane of the lower PCB with via holes, and with additional metalized via holes alongside the microstrip line to form a stopband for parallel-platemodes in the air gap. The designed element can be used in large arrays with distribution networks realized in such microstrip-ridge gap waveguide technology. Therefore, the present paper describes a generic study in an infinite array environment, and performance is measured in terms of the active reflection coefficient S11 and the power lost in grating lobes. The study shows that the radiation characteristics of the array antenna is considerably improved by using a soft surface EBG-type SIW corrugation between each 2x2-slot element in E-plane to reduce the mutual coupling. The study is verified by measurements on a 4x4 element array surrounded by dummy elements and including a transition to rectangular waveguide WR15.

Evaluation of a siPm array coupled to a Gd3Al2Ga3O12:Ce (GAGG:Ce) discrete scintillator

Aim: Silicon Photomultipliers (SiPMs) are relatively insensitive to magnetic fields and thus are good candidates for MR combined applications [1-2]. In this study, we present the results of the SensL ArraySL-4 (4x4 element array of 3x3mm2 SiPMs) photo-detector coupled to a 6x6 GAGG:Ce scintillator array, with 2x2x5mm3 crystal size elements and pitch equal to 2.1mm. Experimental evaluation was carried out with 22Na and 137Cs radioactive sources in terms of energy resolution and peak to valley ratio.

Yttrium ferrite based circularly polarized triangular patch array antenna

In this communication, the circularly polarized properties of 4x4 element planar microstrip equilateral triangular array antenna (METAA) printed on Yttrium ferrite substrate are presented. Two hands of circular polarization are generated when the magnetic bias is applied parallel to the wave propagation in the antenna geometry. The values of antenna parameters of array geometry as radiation conductance, radiation efficiency and bandwidth are investigated for biased and unbiased case. The analysis is based on cavity model.

Yttrium Ferrite Based Circularly Polarized Triangular Patch Array Antenna

In this communication, the circularly polarized properties of 4x4 element planar microstrip equilateral triangular array antenna (METAA) printed on Yttrium ferrite substrate are presented. Two hands of circular polarization are generated when the magnetic bias is applied parallel to the wave propagation in the antenna geometry. The values of antenna parameters of array geometry as radiation conductance, radiation efficiency and bandwidth are investigated for biased and unbiased case. The analysis is based on cavity model.