Lock-in Thermography Characterization of Photothermal Transparent Thin Films

This study evaluates the capabilities of a new Lock-in Thermography device for characterizing photothermal thin films. Lock-in Thermography, a sensitive imaging technique, is used to detect thermal variations, particle aggregation, and material inhomogeneities. The Calorsito device combines multiwavelength infrared illumination with high-resolution thermal spectroscopy, enabling precise analysis of thermal and structural properties.Three photothermal thin films—Fe 3 O 4 , Fe 3 O 4 @Cu 2x S, and Chlorophyllin—were studied to assess their thermal performance. The device measured temperature changes (ΔT) across various infrared wavelengths, which were then compared with Average Visual Transmittance (AVT) measured separately. The results showed that the Calorsito device successfully visualized particle aggregation and heat distribution, providing insights into thin film heat development and homogeneity. Additionally, measurements confirmed that AVT had a stronger influence on ΔT than concentration. Results showed that films with lower AVT exhibited higher ΔT, demonstrating greater light absorption and superior photothermal efficiency. Fe 3 O 4 @Cu 2x S films outperformed others due to the enhanced optical properties of Cu 2x S nanoparticles, making them ideal for light-to-heat conversion applications.