• Alvarado-Gil, J. J.
• Peñuñuri, F.
• Ordonez-Miranda, J.
• Medina-Esquivel, R. A.
• Martinez, P.
• Zambrano-Arjona, M. A.

Abstract

<jats:p>The thermal wave field in a sample of thickness L and optical absorption coefficient β is derived and analyzed, by considering the effects of the multiple reflections of a modulated light beam within the sample. By comparing the corresponding amplitude and phase spectra, in presence and absence of those reflections, it is shown that their effects are strongly determined by the product βL. When the thermal wave field is measured at the illuminated surface, those effects appear remarkably on the amplitude and phase in the thermally thin and thermally thick regimes, respectively, and for βL≲2. The deviation of the amplitude spectrum due to the multiple reflections of incident light beam can be as large as 25%. In contrast, when the thermal wave field is measured at the non-illuminated surface, the contribution of the multiple reflections shows up on both the amplitude and phase in the thermally thick regimes, and for βL≲5. These spectra exhibit deviations of about 20% from their corresponding values without the effects of the light reflections. The obtained results show that the accurate measurement of the thermal and/or optical properties of the sample material, based on the amplitude and phase spectra, requires the consideration of those multiple reflections, especially for the cases where βL≈1. The predictions of the proposed approach for the optical absorption coefficient are in reasonable agreement with the results obtained through an independent technique based on a spectrometer.</jats:p>

Topics

• impedance spectroscopy
• surface
• phase