Infrared thermography is widely used for the inspection of electrical equipment because it enables non-contact measurement of surface thermal fields. However, conventional temperature-based evaluation is sensitive to environmental conditions and often shows limited capability for identifying incipient defects with weak thermal signatures. To address this issue, this paper proposes a quantitative infrared thermographic evaluation method for electrical equipment using joint temperature gradient and temperature features. In this method, temperature gradient feature is used to identify incipient defects, whereas temperature features are used to assess the severity of developed defects. For automated analysis, equipment regions are first localized in thermographic images, and the corresponding temperature gradient and temperature features are then extracted for quantitative condition evaluation. A joint evaluation criterion is further established to integrate incipient abnormality identification with severity-oriented assessment of developed thermal defects. In addition, a dedicated diagnostic instrument is developed to support practical implementation. Experimental results show that, under the present dataset and experimental conditions, a temperature gradient threshold of 4.77 °C/m effectively distinguishes normal and incipient defect states. Compared with the temperature-only strategy, the proposed joint strategy improves the evaluation accuracy from 57.78 % to 86.67 %, corresponding to an absolute gain of 28.89 percentage points, and yields the highest recall of 90.00 % among the compared strategies. These results show that the joint use of temperature gradient and temperature features improves defect sensitivity while supporting severity-aware thermographic evaluation.
The thermal transfer and infrared absorption of zinc-potassium germanate glasses were studied for potential use in infrared laser energy measurements. The volume absorbers containing GeO2 as the glass former, K2CO3 as a fluxing agent to lower the melting temperature, and ZnO as a stabilizer exhibit a higher absorption coefficient in the far-infrared region and thermal properties, such as thermal conductivity, specific heat, and thermal diffusivity, make them useful as absorbers in calorimetric techniques for far-infrared CW lasers. Their structural characteristics exhibit superior properties compared to silicate glasses, widely used as laser light absorbers, enabling thermal detection up to 300 °C with a longer heat-propagation time of up to 0.25 s, in addition to excellent infrared absorbance. Using a platinum thin film as a sink and electrical contact with the thermocouples, a given amount of energy dissipated into the absorber volume has the same effect as the laser beam. These germanate glasses were compared with silicate glasses, widely used as volume absorbers and infrared laser detection. The main thermal transfer parameters, such as thermal conductivity, specific heat, and thermal diffusivity, determine the evolution of the thermal phonon distribution and thermal transfer in these detectors.
We demonstrate a narrow-linewidth, high-energy Tm:YLF laser based on a master oscillator power amplifier (MOPA) configuration. By synergistically integrating Fabry-Perot (F-P) etalon linewidth narrowing, electro-optic Q-switching for short-pulse generation, and two-stage dual-crystal amplification for thermal load management, we overcome the long-standing trade-off between narrow linewidth, high pulse energy, and excellent beam quality in high-repetition-rate 2 μm laser systems. In the oscillator stage, a stable seed pulse is obtained at 100 Hz, with a central wavelength of 1907.3 nm, pulse energy of 6 mJ, pulse duration of 23 ns, and spectral linewidth of 0.19 nm. After two-stage amplification, the pulse energy is scaled up to 77 mJ, with a root-mean-square (RMS) pulse-to-pulse energy fluctuation as low as 0.65% over 1 h, and near-diffraction-limited beam quality factors (M2) of 1.19 (horizontal) and 1.37 (vertical), respectively. This comprehensive performance demonstrates the strong potential of 2 μm laser sources for high-precision long-range differential absorption lidar (DIAL), minimally invasive laser medicine, and high-efficiency mid-infrared nonlinear frequency conversion.
A high-power and high-beam-quality master oscillator power amplifier (MOPA) laser system was presented. Dual-end-pumped plano-plano TEM00 dynamically stable resonator (DSR) was built as the master oscillator. The system has two amplifier groups, each equipped with two stages. Each group of laser amplifiers used spherical aberration self-compensation (SAS) method and the output power increased while the beam quality was effectively improved. Spherical aberrations within the oscillator and the amplifiers were measured both before and after the gain-medium, with subsequent beam quality factors. Experimentally measured and theoretically calculated beam quality factors exhibited close agreement. The beam quality “deteriorates-improves” in the amplifiers periodically, while the output power continues to increase. Finally, 210 W output in continuous-wave (CW) operation was obtained, corresponding to the optical–optical efficiency of 45.7% and the beam quality was near diffraction-limit with M2 factor measured as Mx2 = 1.34 and My2 = 1.28 in the orthogonal directions, respectively.
