The bidirectional reflectance distribution function (BRDF) can effectively characterize the reflectance properties of a target, which can be used to correct infrared remote sensing data and improve the accuracy of remote sensing measurements. When the surface temperature changes, the reflectance characteristics of the target usually change, and it is necessary to carry out BRDF measurements under variable temperature conditions. In this paper, a variable-temperature infrared BRDF measurement system based on a robotic arm is developed to realize high-resolution wide-temperature region measurement of BRDF. To improve the measurement accuracy, the shaping optical path was used to expand the laser beam, combined with the laser level to accurately adjust the three-dimensional coordinates of the robotic arm, and the dichotomy method is used to calibrate the detector nonlinearly. A portable heater suitable for the mechanical arm corner mechanism is developed, and fast and high-precision temperature control is realized by proportional integral derivative (PID) control. The specular and diffuse BRDF distributions were measured at room temperature to verify the effectiveness of the system. The BRDF distribution of SUS314 stainless steel samples with different roughness is measured during two temperature increases from 20 °C to 1000 °C, and the changing rule of BRDF under variable temperature environment is summarized, which provides technical support for evaluating the optical properties of high-temperature materials and improving the measurement accuracy of remote sensing data.

We theoretically and experimentally investigated the fluorescence and transmission readouts of radio-frequency (RF) electrometry based on three-photon-excited Rydberg atoms. We developed a theoretical model for the fluorescence and transmission readout processes of a three-photon-excited Rydberg atom electrometer and performed a qualitative comparative analysis of fluorescence versus probe transmission readouts. Theoretical calculations revealed that while both fluorescence and probe transmission readouts can employ Autler–Townes (AT) splitting to measure strong RF fields, probe transmission readouts become ineffective in weak-field regimes, whereas fluorescence readouts remain sensitive to weak RF fields. Experimentally, we comprehensively characterize the fluorescence response across a wide range of RF field strengths: from the weak-field regime (exhibiting scaling of fluorescence peak amplitude with RF field strength), through the intermediate-field regime (where fluorescence spectral linewidth scales proportionally with RF field strength), to the strong-field regime (characterized by traditional A-T splitting). Furthermore, by adding a narrow slit in front of the photomultiplier tube (PMT) and scanning the slit together with the PMT along the light beam propagation, we exploit fluorescence’s inherent spatial information to directly map the Rydberg excitation profile and local RF field strength. This overcomes the transmission readout’s inherent limitation of providing only path-integrated signals along the probe beam, even by imaging the probe beam with a CCD camera. Our results establish fluorescence readouts as a superior technique for three-photon Rydberg electrometry, offering enhanced wide-range RF field sensing and direct spatial field mapping.

Measuring the emissivity of an infrared radiant sample with high accuracy is important. Previous studies reported on the multi- or two-temperature calibration methods, which used a reference blackbody (or blackbodies) to eliminate the background radiation, and assumed that the background radiation was independent of temperature. However, in practical measurements, this assumption does not hold. To solve the above problems, this study proposes a modified two-temperature calibration method and facility. The two temperature points are set in a certain small interval based on the proposed calculation method; based on the indication of the approximation that the emissivities of the sample and the background radiations remain the same at these two temperatures, the emissivities can be calculated with measurement signals at these two temperatures, and a reference blackbody is not needed. An experimental facility was built up and three samples with emissivities around 0.100, 0.500, and 0.900 were measured in (8~14) μm. The relative expanded uncertainties were 9.6%, 4.0%, and 1.5% at 60 °C, respectively, and 8.8%, 5.8%, and 1.2% at 85 °C (k = 2), respectively. The experimental results showed consistency with the results obtained using other methods, indicating the effectiveness of the developed method. The developed method might be suitable for samples whose emissivities are temperature insensitive.

Non-contact spectroscopic thermometry is widely employed in combustion field monitoring. However, its advancement is currently hindered by the lack of effective metrological traceability and poor consistency among different measurement methodologies. To address these challenges, a "platinum resistance thermometer–Rayleigh scattering–absorption spectroscopy" traceability chain was established in this work to trace Tunable Diode Laser Absorption Spectroscopy (TDLAS) thermometry results back to the International Temperature Scale of 1990. Furthermore, to overcome the spatial resolution limitations inherent in line-of-sight TDLAS measurements, a parameterized temperature-concentration distribution model was developed. Coupled with a novel non-linear multi-line fitting algorithm based on dynamic signal amplitude weighting, this framework enables the precise inversion of temperature and concentration distributions in non-uniform combustion fields. Experiments on a standard McKenna flame validated the noise robustness of the algorithm and the accuracy of the traceability chain. In-situ measurements on a small turbojet engine demonstrated that the system can acquire temperature distributions across multiple operating conditions at a frequency of 50 kHz, accurately capturing transient processes such as ignition and flameout. This work provides a high-precision, traceable diagnostic solution for extreme combustion fields, laying a solid foundation for the standardization and engineering application of spectroscopic thermometry.