Experimental Study On The Measurement Of Directional-hemispherical Spectral Transmittance And Reflectance

With the development of the technologies of effective use of energy, production of functional coating, radiation thermometry and microelectronics technology, a series of surface radiation problems appeared which dominated by thermal radiation. Radiation heat transfer between different surfaces or different infinitesimal surface are requently encountered engineering problems in the field of the thermal power engineering, the use of solar energy and so on. Transmittance and reflectance are very important surface radiation parameters which related to surface condition, orientation, wavelength, they are the basis heat transfer analysis and other scientific research. Thus, accurate measurement for surface transmittance and reflectance is of great importance in the research of improving energy efficiency, new materials and so on.First of all, a variety of existing measurement methods are analysed and summaried in this paper, including their principles, advantages and disadvantages, directionality problem in the process of measurement is studied. The study found that integrating sphere method has the ability of spatial uniformity, and can consider the impact of the scattering sample. Based integrating sphere theory, directional-hemispherical transmittance and reflectance measurement model is established which is based on substitution method. The measurement model mentions substitution error, and then corrects it with theoretical calculation method.Secondly, a directional-hemispherical spectral transmittance and reflectance measurement system based on measurement model is designed. The system consists of light source, splitting system, light guide systems, detection systems and signal acquisition system. It can be used to measure directional-hemispherical spectral transmittance and reflectance witnin 350nm~2500nm, wavelength accuracy is 0.2nm, the resolution is 0.01 nm, if the light trap device is installed, it can be used to measure the mirror reflectance.Linearity of the system is no more than 5%. The transmittance of several typical samples in 350-2500 nm are measured with this system, such as quartz, sapphire. The reflectance of silicon wafers and silicon oxide in 350-2500 nm are measured with this system, and the experimental results are compared with the simulation results. The results show that, in addition to starting low SNR bands, the deviation of experimental measurements and simulation results is less than 2.5%. Experimental results show that the theoretical calculation method of the text can eliminate substitution error. Uncertainty of the measurement system is analyzed from four aspects, such as measurement repeatability, inhomogeneity of diffuse reflection characteristics in the integrating sphere, wavelength inaccuracy and nonlinearity of the system. The overall expanded uncertainty is 5%, fully meet the technical requirements.