The fabrication of transparent and flexible thin film transistors (TFTs), using single-walled carbon nanotube (SWCNT) networks as bottom gates and conducting channels and polymethylmethacrylate (PMMA) as an insulating layer, by the direct transfer method is demonstrated. The fabricated SWCNT-TFTs exhibited a mobility of 23.4 cm2/V s and an ON/OFF current ratio of ∼103. A minor decrease of ∼7% on the performance of the SWCNT-TFTs after bending to a radius of curvature of ∼6 mm was observed. The differences in performance of the devices fabricated with SWCNTs on SiO2/Si and those prepared by transferring SWCNTs onto a polycarbonate substrate are also discussed.
Turbidity Suppression via Optical Phase Conjugation (TS-OPC) is an optical phenomenon that uses the back propagation nature of optical phase conjugate light field to undo the effect of tissue scattering. We use the computationally efficient and accurate pseudospectral time-domain (PSTD) simulation method to study this phenomenon; a key adaptation is the volumetric inversion of the optical wavefront E-field as a means for simulating a phase conjugate mirror. We simulate a number of scenarios and demonstrate that TS-OPC deteriorates with increased scattering in the medium, or increased mismatch between the random medium and the phase conjugate wave during reconstruction.
We report what we believe to be the first rigorous numerical solution of the two-dimensional Maxwell equations for optical propagation within, and scattering by, a random medium of macroscopic dimensions. Our solution is based on the pseudospectral time-domain technique, which provides essentially exact results for electromagnetic field spatial modes sampled at the Nyquist rate or better. The results point toward the emerging feasibility of direct, exact Maxwell equations modeling of light propagation through many millimeters of biological tissues. More generally, our results have a wider implication: Namely, the study of electromagnetic wave propagation within random media is moving toward exact rather than approximate solutions of Maxwell's equations.
[1] We report a full-vector, three-dimensional, numerical solution of Maxwell's equations for optical propagation within, and scattering by, a random medium of macroscopic dimensions. The total scattering cross section is determined using the pseudospectral time domain technique. Specific results reported in this paper indicate that multiply scattered light also contains information that can be extracted by the proposed cross-correlation analysis. On a broader perspective, our results demonstrate the feasibility of accurately determining the optical characteristics of arbitrary, macroscopic random media, including geometries with continuous variations of refractive index. Specifically, our results point toward the new possibilities of tissue optics; by numerically solving Maxwell's equations, the optical properties of tissue structures can be determined unambiguously.
The Monte Carlo simulation of light scattering by a cluster of dielectric spheres is compared with numerical solutions of Maxwell's equations via the pseudospectral time-domain technique. By calculating the total scattering cross-section ͑TSCS͒ spectrum, respectively, the spectral light scattering characteristics are determined. Since the Monte Carlo simulation falls short to accurately account for coherent interference effects, it is shown that the Monte Carlo simulation yields TSCS spectra that significantly deviate from the numerical solutions of Maxwell's equations. Therefore, it is necessary to resort to Maxwell's equations in order to accurately determine the light scattering characteristics of a macroscopic geometry.
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