Study on the measurement sensitivity for optical coatings absorption loss by the photothermal detuning technique

The photothermal detuning technique (PTDT) is a novel photothermal technique and can be used to measure the absorption of the optical coatings, which utilizes the spectral shift of optical coatings caused by absorption-induced temperature rise. The measurement sensitivity depends on the slope of the spectrum band edge and the character of the probe beam, and is limited by the temperature coefficient of the reflectivity or transmission. Based on the preliminary study, the impact of the spectrum band slope and the probe beam character on the measurement sensitivity are detailed studied. Experiments are performed with a highly reflective coating. The results show that the measurement sensitivity is determined by the structure and the optical-thermal parameters. Appropriate wavelength, incident angle and polarization properties of the probe beam can improve the measurement sensitivity. The results provide a theoretical and experimental basis for the application of the photothermal detuning technique for absorption loss of the thin film.