Hefei University of Technology developed a new laser heat source spatial modulation technology

[ Instrument Network Instrument Development ] Recently, Prof. Lu Rongsheng from the School of Instrument Science and Optoelectronic Engineering of Hefei University of Technology proposed a new laser heat source spatial modulation technology to achieve a significant increase in the sensitivity and efficiency of laser-induced photothermal detection of optical materials. Strong laser material development, strong laser component preparation and strong laser system implementation have important application value. This achievement was recently published in the Applied Physics Journal of Applied Physics, Applied Physics Letters, Vol. 114, No. 13, 2019, and was selected for the current featured article and AIP Scilight.

Large-scale intense laser and laser nuclear fusion research is of great significance to improve overall national strength. Due to the extremely high laser energy, the system components are extremely demanding on the quality of optical materials. It is one of the key technologies to detect the optical absorption and thermal properties of a large number of optical materials in related equipment. At present, the laser-induced photothermal detection technology adopted by relevant scientific research equipment in China induces the periodic local temperature rise of the material by the time modulation of the pump laser energy, and measures the modulation amplitude of the corresponding periodic thermoelastic deformation to the detection laser, and acquires and enhances Detection signal. However, due to the extremely small optical absorption and thermal expansion coefficient of the optical material in the strong laser system, the local temperature difference and the thermoelastic deformation amplitude of the material are small, which limits the sensitivity of photothermal detection. The point-by-point detection of large-sized components takes a lot of time, and its use efficiency is extremely low.

The team found that when the laser heat source moves uniformly on the surface of the material to be tested, the heating of the material can be divided into two processes: transient and quasi-steady state. The heat accumulation effect in the quasi-steady-state heating process increases the current spitting of the material. The peak temperature of the spot, after a certain cooling time, the irradiated point will be cooled to the ambient temperature to obtain the temperature valley. Due to the large difference between the peak and the valley, the local temperature difference and thermoelastic deformation of the irradiation point are greatly improved, and high-sensitivity photothermal detection is realized.

According to the team member and the first author of the thesis, Dong Jingtao, this achievement successfully overcomes the problem of the local temperature difference and the thermoelastic deformation of the optical materials produced by the current time-modulated laser-induced photothermal detection technology.

The team's experimental results for fused silica samples show that under the same experimental conditions, the sensitivity of this new modulation method is 1.8 times that of the existing method, and it can capture weak absorption defects that cannot be detected by existing methods. At the same time, this technology can achieve flight measurement, which greatly improves the detection efficiency of large-size components.

The achievement was funded by the National Natural Science Foundation of China (51805138), the basic research business fees of the Central University (JZ2018HGBZ0126, JZ2019HGTB0085) and the Anhui Provincial Laboratory of Non-Smooth Surface Nondestructive Testing (CGHBMWSJC02).

(Original title: Institute of Instrument Science and Optoelectronic Engineering, Hefei University of Technology, research and development of new laser heat source spatial modulation technology)