Investigation of Free Space Optical Detection Module Operating at the Wavelength Range of 8-12 μm
The paper presents the construction and test results of a long-term radiation detector module for free space optical communication operated at the wavelength range of 8–12 μm. In the module a Polish detector manufactured in the company Vigo System S.A. was applied. High sensitivity of the detection module was achieved through a multi-layered heterostructure HgCdTe with immersion lens, which is optimized for the radiation detection at the wavelength of 10 μm. Detector noises were reduced as a result of detector cooling by means of four-stage thermoelectric cooler. The developed detection module is dedicated to design a next-generation optical data link. The link will be characterized by a greater range in difficult weather conditions in relation to the currently offered links operating at the shorter wavelengths.
Physical and Gas Transport Properties of Novel Hyperbranched Polyimide – Silica Hybrid Membranes
SummaryPhysical and gas transport properties of novel hyperbranched polyimide – silica hybrid membranes were investigated. Hyperbranched polyamic acid as a precursor was prepared by polycondensation of a triamine monomer, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and a dianhydride monomer, 4,4’-(hexafluoro-isopropylidene)diphthalic anhydride (6FDA), and subsequently modified the end groups by 3-aminopropyltrimethoxysilane (APTrMOS). The hyperbranched polyimide – silica hybrid membranes were prepared using the polyamic acid, water, and tetramethoxysilane (TMOS) via a sol-gel technique. 5 % weight-loss temperature and glass transition temperature of the hyperbranched polyimide – silica hybrid membranes determined by TG-DTA measurement considerably increased with increasing silica content, indicating effective cross-linking at polymer – silica interface mediated by APTrMOS moiety. CO2, O2, and N2 permeability coefficients of the hybrid membranes increased with increasing silica content. It was pointed out that the increased gas permeabilities are mainly attributed to increase in the gas solubilities. On the contrary, CH4 permeability of the hybrid membranes decreased with increasing silica content because of decrease in the CH4 diffusivity and, as a result, CO2/CH4 selectivity of the hybrid membranes remarkably increased. It was concluded that the 6FDA-TAPOB hyperbranched polyimide – silica hybrid membranes have high thermal stability and excellent gas selectivity, and are expected to apply to a high-performance gas separation membrane.
HgCdTe buried multi-junction photodiodes fabricated by the liquid phase epitaxy
Abstract This article reports the parameters and characteristics of the new type of HgCdTe buried photodiodes operated at near-room temperature (T=200–300 K) in long wavelength infrared spectral range. The liquid phase epitaxy (LPE) Hg1−xCdxTe (x=0.16–0.20) layers were grown on holes etched in (1 0 0) CdZnTe substrate. Prior to layer deposition, the CdZnTe substrate has been etched to form the bars on 30 μm centers and 20-μm depth. Next, 20-μm thick HgCdTe epitaxial layer has been grown from Te-rich solution. The type of conductivity was controlled by deliberately doping with indium (n-type) and Sb (p-type). The Nomarski microscopy showed that the surface of specially prepared layers was flat and the composition of layers, measured by Fourier transform infrared microscopy, was homogenous. Samples were cleaved and examined in cross section by scanning electron microscopy. Finally, serial connected multi-junction photodiodes have been fabricated. It is shown that LPE can be used to realise advanced bandgap engineered multi-junction structures. This conclusion is supported by device quality characteristics: spectral response and detectivity.