Dr. Shufang He Profile

Dr. Shufang He

at National Institute of Metrology

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Publications (4)

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Proceedings Article | 30 April 2024 Paper

Research of non-linearity correction in infrared spectral radiance measurement

Shufang He, Ruoduan Sun, Yanfei Wang, Caihong Dai, Jinyuan Liu, Guojin Feng, Jinghui Wang

Proceedings Volume 13154, 131540G (2024) https://doi.org/10.1117/12.3018626

KEYWORDS: Infrared radiation, Black bodies, FT-IR spectroscopy, Spectral response

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The nonlinear effect is one of the characteristics of photodetectors. In infrared measurement systems, photodetectors like MCT, InGaAs and InSb are widely used; while their non-linearity is still a problem. National Institute of Metrology, China has built an infrared spectral radiance measurement system. The system consists of a variable temperature blackbody as the standard radiation source; and uses a Fourier transform Infrared Spectrometer as the measuring instrument, including a MCT detector which is the main source of non-linearity uncertainty. In this study, an interpolation method and a polynomial fitting method are used to correct the non-linearity of the measurement system. To do so, at first, set the temperature of the standard variable blackbody to a serial of different temperatures, and use the measurement system to acquire the spectral response signal at each temperature; then, calculate the spectral radiance value of the standard radiation source based on the Planck’s law; after that, in the spectral dimension, analyze the relationship between and , and correct its non-linearity with a piecewise linear interpolation method and a multi-order polynomial fitting method; finally, verify the above two methods and analyze the relative deviation accordingly. The results show, the deviation is relatively large in wavelength range smaller than 8μm; while in 8μm~14μm wavelength range, the relative deviation is around 0.5%~0.001% and around 1.0%~0.001% by using the piecewise linear interpolation method and polynomial fitting method, respectively.

Proceedings Article | 18 April 2021 Poster + Presentation + Paper

Research of UV radiometer based on fiber spectroradiometer

Yanfei Wang, Caihong Dai, Ling Li, Zhifeng Wu, Ning Xu, Chaoqun Xu, Qiutong Cheng, Shufang He, Yihang Xie

Proceedings Volume 11772, 1177226 (2021) https://doi.org/10.1117/12.2593578

KEYWORDS: Ultraviolet radiation, Radiometry, Stray light, Temperature metrology, Light sources, Ultraviolet sources, Sensors, Optical testing, Lamps, Environmental sensing

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UV radiometers are used in many areas. There are many kinds of UV light sources with different peak wavelength and different wavelength range. The broadband UV radiometers are wildly used due to easy to use and low cost. However, there are some obvious disadvantages for the broadband radiometers. They cannot distinguish the spectral characteristics of UV sources. That will cause the spectral mismatch measurement error for the UV broadband radiometers calibration. Recently, the fiber spectroradiometer plays a more and more important role in this area. The fiber spectroradiometer is more portable and low cost compared to the double grating spectroradiometer. We can obtain the spectral characteristics and any UV irradiance using the fiber spectroradiometer. However, for most fiber spectroradiometers, we cannot use them to replace the UV broadband radiometers for the absolute irradiance measurement. There are four key effects for that. The first one is the stray light. Stray light effect is obvious for the fiber spectroradiometer, especially in the UV wavelength range. The second one is the temperature effect. The third one is the non-linearity effect. The fourth one is the bandwidth effect. This effect will cause the measurement error for the spectral distribution of the UV source. In this paper, we research the four factors that reduce the measurement accuracy of the fiber spectroradiometer in UV wavelength range.

Proceedings Article | 18 December 2019 Paper

Analysis and suppression of stray radiation in infrared spectral radiation measurement

Shufang He, Yanfei Wang, Caihong Dai, Jinyuan Liu, Guojin Feng

Proceedings Volume 11337, 1133704 (2019) https://doi.org/10.1117/12.2540466

KEYWORDS: Infrared radiation, Optical simulations, FT-IR spectroscopy

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The absolute measurements of spectral radiance, irradiance and intensity in infrared wave range are very important for infrared target recognition, material emissivity measurement and so on. Recently, many researchers focus on how to accurately measure absolute infrared spectral radiation, in which one key point is how to suppress stray radiation. In this paper, an absolute infrared spectral radiance measurement system was built up. The system contained a fixed-point blackbody source, a variable temperature blackbody source, a radiant source to be measured, Fourier Transform Infrared Radiometer (FTIR), optical system, non-contact infrared thermometer and so on. Emissivities of the standard source and the radiant source to be measured are 0.999 and 0.995, respectively. According to Planck’s law, their absolute spectral radiance should be similar at the same radiation temperature. In experiment, temperatures of the standard blackbody and radiant source to be measured were set to 500°C, and the FTIR was used to measure spectral radiance. The results show spectral radiance of the standard source is 14.9% smaller than the radiant source to be measured at 10μm wavelength. A thermal infrared imager and optical simulation software were used to analyze the possible reasons. To solve the problems, a shielding plate and a field aperture was installed respectively at the entrance of the optical system and before the FTIR to suppress stray radiation. Moreover, sizes and positions of the shielding plate, optical system, and field aperture were analyzed by optical simulation software and mathematical calculation. After optimization, the experimental results show the difference of spectral distributions between the standard source and the radiant source to be measured is only 1.42% at 10 μm wavelength, suggesting stray radiation is effectively suppressed in the system.

Proceedings Article | 18 November 2019 Paper

System construction and uncertainty evaluation of absolute measurement of infrared spectral radiance

Shufang He, Yanfei Wang, Caihong Dai, Jinyuan Liu, Guojin Feng

Proceedings Volume 11189, 111891A (2019) https://doi.org/10.1117/12.2537206

KEYWORDS: Infrared radiation, FT-IR spectroscopy, Radiometry, Optical metrology

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The absolute measurement of infrared spectral radiance is very important for optical radiometry. In this paper, a system for absolute measurement of infrared spectral radiance is built up. The system consists of fixed-point blackbody sources, a variable temperature blackbody, a radiant source to be measured, Fourier Transform Infrared Radiometer (FTIR), relay optical system, non-contact infrared thermometer and so on. The emissivity of the variable temperature blackbody is 0.999; the temperature range is 50°C ~ 1050°C. The emissivity of the radiant source to be measured is larger than 0.995; the temperature range is 30°C ~ 550°C. The variable temperature blackbody source was calibrated and can be traced to the fixed-point blackbody source. In experiment, it was used as the standard radiant source. The spectral range of this system is 3 μm ~ 14 μm. A serial of experiments have been implemented to analyze the uncertainty of each component, including the repeatability, size-of-source effect, stability, uniformity and so on. To improve the system’s uncertainty, we have suppressed stray radiation and optimized optical system by installing a water-cooled aperture and a field stop at the entrance of the optical system and before the FTIR, respectively; optimizing the system based on optical simulation and replacing the reflective mirrors with one off-axis parabolic mirror. Next step, we will re-evaluate the uncertainty of the improved system.

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