Whispering gallery mode (WGM) resonators have been extensively studied in optical range, however, they still have great research potential in terahertz (THz) domain. In this paper, the electric-field distribution of ~0.46 THz in high resistivity float zone silicon (HRFZ-Si) microring resonator was analyzed. By simulating the instantaneous heat dissipation process, thermal relaxation time was obtained which characterizes how fast the heat transfer from mode volume to the substrate. Furthermore, the optothermal dynamics within the resonator was depicted by an ordinary differential equation where both the linear absorption and the nonlinear Kerr effect were accounted. A series of transmission spectra under various input power were simulated. The results showed that unlike the case of optical regime, THz WGM exhibits obvious broadening under high injection power (over 80 mW) due to the relatively high absorption. The study will promote the understanding of interaction between THz wave and matter.
KEYWORDS: Temperature metrology, Absorption, Copper, Magnetism, Doppler effect, Digital breast tomosynthesis, Thermodynamics, Cesium, Aluminum, Calibration
With the redefinition of the Boltzmann constant and the basic international temperature unit of Kelvin, the international agreement on temperature scale is gradually transferred to the thermodynamic temperature scale. Based on the Doppler broadening of the cesium atom’ absorption spectrum the thermodynamic temperature of cesium atom cell can be measured. The accuracy of temperature measurement and the verification of experimental principle depend on the surrounding temperature stability of the absorption cell. In this paper, a thermostatic chamber with precise temperature control system was designed and realized. The thermostatic chamber consists of an aluminum cavity, a support layer, a shielding layer, a heat insulation layer and a copper column. The influence of size and material parameters on temperature control effect was analyzed by finite element method. Based on theoretical analysis, the structure of the chamber was optimized. In the experiment, circulating water cooling was used to provide the base temperature for the cavity. A negative feedback control program was developed to regulate the heating power of the electric heating film to achieve rapid temperature regulation and stabilization. The maximum temperature difference of the copper column inside the constant temperature chamber with a length of 380 mm and a diameter of 210 mm was less than 8 mK. The temperature fluctuation within 12 hours were less than 1 mK and the temperature stability was less than 0.16 mK, and the standard uncertainty of the camber temperature was 11.02 mK. This study will improve the development of the calibration-free, chip-scale thermodynamic temperature sensors.
KEYWORDS: Black bodies, Monte Carlo methods, Infrared radiation, Temperature metrology, Ray tracing, Reflectometry, Integrating spheres, Metrology, Infrared materials, Environmental sensing
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 %.
Temperature is a critical parameter to diagnose the high temperature hypersonic combustion flow. A fiber-spectrometer
based measurement system and the correlated theoretical models to measure the radiation temperature of the “optical
thick” hypersonic combustion flow were established in this paper. The spectral responsivity of the fiber-spectrometer
based measurement system was measured at NIM in lab condition, and the spectral radiance and emissivity of the
hypersonic combustion flow were measured in-situ at the combustion wind tunnel of BISLMV. Preliminary experimental
results showed the spectral emissivity of the combustion flow was about 0.1 in the spectral range 500-800nm without
strong spectral selection, which resulted in the radiation temperature about 2200 K, with relative standard uncertainty
about 10%.
A high speed, high resolution spectrum measurement system based on fiber-spectrometer was built to diagnose the high
temperature hypersonic combustion flow. The theoretical models of the spectral radiance and transmittance of the
hypersonic combustion flow were established in this paper. The spectral radiance and transmittance of the hypersonic
combustion flow were measured at the combustion wind tunnel of BISLMV. Preliminary experiments showed that the
spectral radiance behaved not like typical gas radiation but have a continuous spectrum, and the spectral transmittance of
the combustion gas flow was about 0.9 in the spectral range 500-900nm without strong spectral selection. The results
obtained in this paper will benefit the surface temperature measurement of the thermal protection materials of space
vehicle tested at BISLMV.
KEYWORDS: Temperature metrology, Black bodies, Radiation thermometry, Pyrometry, Radiative energy transfer, Prototyping, Actuators, Process modeling, Statistical modeling, Heat flux
Spectral emissivity is one of the most critical thermophysical properties of a material for heat design and analysis. Especially in the traditional radiation thermometry, normal spectral emissivity is very important. We developed a prototype instrument based upon an integral blackbody method to measure material’s spectral emissivity at elevated temperatures. An optimized commercial variable-high-temperature blackbody, a high speed linear actuator, a linear pyrometer, and an in-house designed synchronization circuit was used to implemented the system. A sample was placed in a crucible at the bottom of the blackbody furnace, by which the sample and the tube formed a simulated reference blackbody which had an effective total emissivity greater than 0.985. During the measurement, a pneumatic cylinder pushed a graphite rode and then the sample crucible to the cold opening within hundreds of microseconds. The linear pyrometer was used to monitor the brightness temperature of the sample surface, and the corresponding opto-converted voltage was fed and recorded by a digital multimeter. To evaluate the temperature drop of the sample along the pushing process, a physical model was proposed. The tube was discretized into several isothermal cylindrical rings, and the temperature of each ring was measurement. View factors between sample and rings were utilized. Then, the actual surface temperature of the sample at the end opening was obtained. Taking advantages of the above measured voltage signal and the calculated actual temperature, normal spectral emissivity under the that temperature point was obtained. Graphite sample at 1300°C was measured to prove the validity of the method.
Spectral emissivity is a critical material’s thermos-physical property for heat design and radiation thermometry. A prototype instrument based upon an integral blackbody method was developed to measure material’s spectral emissivity above 1000 ℃. The system was implemented with an optimized commercial variable-high-temperature blackbody, a high speed linear actuator, a linear pyrometer, and an in-house designed synchronization circuit. A sample was placed in a crucible at the bottom of the blackbody furnace, by which the sample and the tube formed a simulated blackbody which had an effective total emissivity greater than 0.985. During the measurement, the sample was pushed to the end opening of the tube by a graphite rod which was actuated through a pneumatic cylinder. A linear pyrometer was used to monitor the brightness temperature of the sample surface through the measurement. The corresponding opto-converted voltage signal was fed and recorded by a digital multi-meter. A physical model was proposed to numerically evaluate the temperature drop along the process. Tube was discretized as several isothermal cylindrical rings, and the temperature profile of the tube was measurement. View factors between sample and rings were calculated and updated along the whole pushing process. The actual surface temperature of the sample at the end opening was obtained. Taking advantages of the above measured voltage profile and the calculated true temperature, spectral emissivity under this temperature point was calculated.
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