Experimental Study On Spectral Radiative Properties Of Optical Windows And Porous Foam Material At High-temperature

Thermal radiation transfer is one way of energy transmission in the form of electromagnetic wave,as well as a transmission means of thermo-optical signal.In a lot of relevant scientific research and engineering,the thermo-optical properties of semitransparent materials cannot be slighted.Due to the implicit volumetric and directional feature of the thermal radiation transfer in semitransparent materials,to reveal the transmission behavior needs a lot of experimental measurement and quantitative analysis.The study on thermal radiation properties of semitransparent materials is actually the research on the inverse thermal radiation problem,which involves measurements on apparent radiative properties,the simulation on the experiment,and the identification of thermal radiation parameters of the medium.The research is a very important basic topic in the thermal radiation field referring experimental measurement and numerical simulation.The derived results can be used to feed the applications involving energy volumetric distribution and thermal optical signal transmission.For the typical semitransparent materials such as the fused silica,the alumina crystal and the alumina foam,studies on measuring methods of apparent properties,the experimental set-up,measurements on transmitted and reflected properties,experimental uncertainty evaluation,as well as identification of radiative properties of the medium were carried out.The volumetric and directional characteristic of apparent radiative properties were used to develop measurement methods.The multi-thickness method and the stacking-interface method were proposed for absorbing media,in order to acquire various transmitted and reflected properties in both highly transparent and semitransparent spectra.The multi-thickness method and the method of multidimensional geometric effect were claimed for the highly porous foam,which can be used to derive transmitted and reflected properties in the highly scattering spectrum with high signal-to-noise ratio.The applied scope of the multi-thickness method and the stacking-interface method were discussed,as well as the geometric effect of the cylindrical sample,the spheroidal sample,the conical sample.An infrared experimental system for measuring high-temperature directional-directional spectral properties of transmission and reflection was built,with the measured temperature range of 300-1800K and the spectral range of 0.85-25?m.The prevacuum-argon heater was designed,which can form a isothermal zone with the maximum temperature difference of less than 10K.Heating a sample in the isothermal zone,avoiding the disadvantage of heating temperature gradient inside the sample.A rotatable sample holder at high-temperature was developed with the rotation range of±180oand the rotation precision of 0.01o,which is controlled by the stepping motor and the computer.Various high-temperature directional-directional properties of transmission and reflection can be measured when the sample was moving,combining the optical paths in the heating chamber.The high-temperature measure model for measuring properties of transmission and reflection was deduced based on the Fourier optics and the analysis on the stray radiation.With this model,the stray noise and the zero drift noise in the spectrogram output by the FTIR spectrometer can be effectively reduced.Using the ZnSe standardized sample made by Thorlabs,the instrument function in the model was derived by the absolute calibration method.Its spectral feature was also discussed.Measurements on the fused silica,the Al₂O₃ crystal and the Al₂O₃ foam were performed.The related experimental uncertainty was evaluated.The evaluation result indicate that it was less than 0.005.Analysis on the typical directional-directional properties of transmission and reflection was done,where,the fused silica at the temperature range of 300-1800K and within 0.85-5.0?m,the Al₂O₃ crystal at the temperature range of 300-1800K and within0.85-7.0?m,and the Al₂O₃ foam at the temperature range of 300-1200K and within0.85-3.0?m.The improved GA identification code was developed,adding advanced GA technologies such as exponential coding,the local optimization algorithm and the elitist strategy.The refractive index,the absorption index,the extinction coefficient and the albedo of the measured materials were retrieved from the experimental data.The absorbing bands at the neighborhoods of 1.4?m,2.2?m and 2.75?m varying nonmonotonicly with temperature was found for the fused silica.The blue shift of high-transparency edge of the Al₂O₃ crystal was revealed.And the scattering albedo within 0.85-3.0?m of the Al₂O₃ polycrystalline foam was found to be nearly 1.0.