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Low size-of-source effect (SSE) infrared optical system design and experimental validation are critically involved. SSE is commonly explored in infrared radiation measurements. The main causes of SSE are the diffraction of the field aperture, the reflection of optical components and objective aberrations. The optical path design and the internal components scattering have an important influence on SSE. Reflective optical system is commonly used in infrared radiation measurements with high temperature region and wide wavelength range, which can eliminate chromatic aberration and reduce coma. A reflective infrared optical system is designed and built based on the high-temperature Fourier transform infrared (FTIR) spectrometer infrared radiation measurement facility at NIM. The ambient scattered radiation and the thermal effect of optical components are controlled via the water-cooled scattered radiation shielding bin and limitation apertures. Experimental validation of the SSE characteristics of the FTIR infrared optical system is carried out via the uniform blackbody radiation source at 500 °C and various sized apertures using the direct measurement method. The corresponding calculation model will be described in the paper. SSE on 3.9 μm is measured via the direct measurement method by using a standard reference blackbody with good temperature uniformity as the radiation source. The effect of reflection is reduced via the high emissivity coating on the apertures. The results show that the effect of the SSE on the FTIR measurement facility at the wavelength of 3.9 μm is less than 2×10-4. Details and results of the infrared optical system SSE measurement will be reported in the paper. All measurements can be traceable to the National Standards of P. R. China.

Integrated blackbody is a blackbody radiation source with the emissivity approximate to 1, which is coupled of materials with different infrared emissivity as the cavity wall and the cavity bottom. The integrated blackbody theory is the theoretical basis of materials infrared spectral emissivity measurement device at ultra-high temperature developed by National Institute of Metrology, China (NIM). Infrared emissivity is the most important factor for evaluating the infrared radiation characteristics of integrated blackbody. Based on Monte Carlo simulation, infrared emissivity of the integrated blackbody coupled of different high emissivity materials and infrared emissivity of the integrated blackbody coupled of low emissivity material and high emissivity material are calculated theoretically in the near infrared wavelength band at room temperature and high temperature environment. The simulation results show that, the infrared emissivity of the integrated blackbody coupled of different high emissivity materials can reach 0.998 and the infrared emissivity of the integrated blackbody coupled of low emissivity material and high emissivity material can reach 0.988. The above simulation results of integrated blackbody infrared emissivity have reached the requirements of industrial blackbody radiation source. The simulation results are verified based on the method of blackbody infrared emissivity measurement by integrating sphere reflectometer at room temperature environment at wavelength of 0.633 μm. Measurement results on multiple wavelengths show that the deviation between the integrated blackbody infrared emissivity simulation results and the measurement results is less than 0.3 %.

Accurate measurement of the material surface temperature plays a vital role in many scientific and technological advances. With the application of the active infrared laser radiation thermometry, the surface temperature can be obtained independently of the target emissivity. This method has been developed gradually, but there is still lacking of the experimental result about low emissivity surfaces, and the determination of the system core parameter has not been sufficiently discussed. Therefore, a new active infrared laser radiation thermometry system is reported in this paper. The temperature change radiance signals emitted from the target surface at the same frequency as the heating laser are accurately screened and collected by using a lock-in amplifier, and the calibration method of the instrument constant is discussed. The experimental results show that, for high emissivity sample, in the range of 873–1173 K, the relative deviation between the temperature measurement results of the experimental device and the reference value is within 0.5%. For the low emissivity sample, also in the range of 873–1173 K the relative deviation between the measurement results of the experimental device and the reference temperature is within 0.8%, and the average absolute deviation is 3.3 K. The measurement accuracy is improved and compared with previous literature.

The spectral responsivity of Fourier Transform Infrared Spectrometer (FTIR) measurement system of high temperature blackbody infrared radiation characteristics is calibrated via ThermoGage HT9500 high temperature reference blackbody furnace from National Institute of Metrology, China (NIM). A calculation model of the spectral responsivity calibration of FTIR measurement system is established. The infrared spectrum of the blackbody radiation source is measured in the temperature range from 1273 K and 1973 K on the wavelength range from 1 μm to 14 μm. Calibration is carried out within the temperature range from 1373 K to 1873 K on the wavelength range between 1 μm and 13 μm. The infrared spectral radiation characteristics of ThermoGage HT9500 high temperature reference blackbody furnace are represented. The results indicated that the method of piecewise linear calibration was practicable. The measured infrared spectrum in the temperature range from 1373 K to 1873 K on the wavelength range between 1 μm and 13 μm was compared with the calculation which showed the signal divergence less than 1%. And the calculated temperature obtained by inverse calculation in this temperature region was compared with the actual temperature which showed the temperature divergence less than 0.45%.

The Fourier-Transform infrared (FTIR) spectrometer is a commonly used instrument in infrared radiation measurements. An infrared spectral emissivity measurement facility using a deuterated tri-glycine sulfate (DTGS) detector has been set up at the National Institute of Metrology, China (NIM). The linearity of the spectral responsivity is one of the main uncertainty contributions in spectral-emissivity measurement, performed over a wide spectral radiance range (0–30,000 W/(m2·sr·μm)). Using the flux superposition method, a double-aperture method, where the apertures are positioned precisely by a cage structure, has been used to measure the linearity of the FTIR measurement system, a sub-system of the infrared spectral emissivity measurement facility, developed at NIM. The drift characteristics of the blackbody radiation sources and the FTIR measurement system during a typical linearity measurement have been investigated. Drifts of the blackbody sources are reduced by integration of the spectrum. The quasi-linear drifts of the FTIR measurement system are corrected by inverting the measurement sequence of the apertures. Moreover, corrections for the effects of aperture imperfections on the linearity measurement have been quantified experimentally. Measurements are reported for blackbody radiation sources in the temperature range (473–1273 K), with detection at the wavelengths 3.9 μm and 10.6 μm, respectively.

Pyromark 1200 (Tempil Co, USA), which is a type of high-temperature high-emissivity coating, is silicon-based with good thermal radiation performance. Its stably working condition is at the temperature range 589~922 K thus a wide range of applications in industrial, scientific research, aviation, aerospace and other fields. Infrared emissivity is one of the most important factors in infrared radiation characteristics. Data on infrared spectral emissivity of Pyromark 1200 is in shortage, as well as the reports on its infrared radiation characteristics affected by its spray painting process, microstructure and thermal process. The results of this research show that: (1) The coating film critical thickness on the metal base is 10μm according to comparison among different types of spray painting process, coating film thickness, microstructure, which would influence the infrared radiation characteristics of Pyromark 1200 coating. The infrared spectral emissivity will attenuate when the coating film thickness is lower or much higher than that. (2) Through measurements, the normal infrared radiation characteristics is analyzed within the range at the temperature range 573~873 K under normal atmospheric conditions, and the total infrared spectral emissivity of Pyromark 1200 coating is higher than 0.93 in the 3~14 μm wavelength range. (3) The result of 72-hour aging test at the temperature 673 K which studied the effect of thermal processes on the infrared radiation characteristics of the coating shows that the infrared spectral emissivity variation range is approximately 0.01 indicating that Pyromark 1200 coating is with good stability. Compared with Nextel Velvet Coating (N-V-C) which is widely used in optics field, Pyromark 1200 high-temperature coating has a higher applicable temperature and is more suitable for spraying on the material surface which is in long-term operation under high temperature work conditions and requires high infrared spectral emissivity.