New heating method makes photothermal detection even more sensitive
New heating method makes photothermal detection even more sensitive lead image
In photothermal detection a sample is heated with radiation, which changes its thermodynamic properties. Measuring these changes reveals the sample’s optical absorption and other properties.
Highly sensitive photothermal detection is needed to measure optical losses and weak absorptive defects of samples used in high-power laser applications. Traditionally, the irradiating heat source is temporally modulated during photothermal detection, and the sensitivity is increased by optimizing optical parameters based on diffraction theory.
Dong et al., however, proposed a new heating method to increase the sensitivity of photothermal detection. Instead of temporally modulating the heat source, the researchers spatially modulated the heat source so that it was moving at a constant velocity. When they tested their method experimentally on fused silica glass, they found that the sensitivity increased by a factor of 1.8 compared to the traditional temporal modulation method.
Heating and cooling cycles account for this dramatic increase in sensitivity. While the site being irradiated reaches a stable, high peak temperature, the previously-irradiated sites are cooling and may have temperatures as low as the ambient temperature. This large temperature difference between sites results in a strong thermoelastic response that allows for highly sensitive photothermal detection.
Lead author Jingtao Dong said that, in addition to significantly improving the sensitivity, spatial modulation of the heat source provides another advantage: Because the heat source is moving at a constant velocity, “on-the-fly,” or high-throughput, detection is possible. In the traditional photothermal detection method, the heating and cooling cycles are implemented at a stationary site of the material, which makes it impossible to carry out high-throughput detection.
Source: “Spatial modulation of heat source for highly sensitive photothermal detection,” by Jingtao Dong, Tengda Zhang, Yuzhong Zhang, Lei Yang, and Rongsheng Lu, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5080163 .
