Mathematical modelling for opto-thermal measurements on optical and thermal gradient materials

Abstract

We present a theoretical study for opto-thermal measurements on non-homogenerous materials, namely the optical gradient materials and the thermal gradient materials. We first present a general opto-thermal mathematical model for gradient materials. Then, we discuss the effects of non-homogenerous optical properties and thermal properties in initial temperature depth profiles, Green's function, transient temperature field and opto-thermal signals.

Photothermal Radiometry Data Analysis by Using Machine Learning

“…Figure 1 shows the schematic diagram of opto-thermal transient emission radiometry (OTTER). It uses a pulsed laser (Er:YAG laser, 2.94 µm, a few milli joules per pulse) as a heat source to heat the sample, an ellipsoidal mirror, and a fast infrared MCT (mercury cadmium telluride (InfraRed Associates, Inc., Stuart, FL, USA) detector to measure the consequent blackbody radiation increase of the sample [31,32]. The MCT detector used is the most sensitive infrared detector on the market.…”

“…The OTTER detection depth is about 20 µm. No other techniques can perform depth-profiling in this range on in-vivo samples [32]. The OTTER skin measurements, therefore, should only be confined within the stratum corneum, which is the outermost skin layer.…”

“…Li Voti et al have developed photothermal depth profiling by genetic algorithms [31]. Xiao et al have conducted a review of the field including photothermal depth profiling techniques [32,33].…”

“…In this paper, we use machine learning to analyze our own measurement data by using opto-thermal transient emission radiometry (OTTER), which is a type of photothermal radiometry technique that has been used in skin hydration, hydration depth profiling, skin pigments, and trans-dermal drug delivery studies [32][33][34][35][36][37][38][39]. Compared with other technologies, OTTER has the advantages of being non-contact, non-destructive, quick to make a measurement (a few seconds), and being spectroscopic in nature.…”

Phototermal Spectra of Inhomogeneous Coatings

“…In the last few years, much effort has been made in the study of photothermal effects in thermally inhomogeneous solids [2][3][4][5]. The main problem arises from the impossibility of solving the inhomogeneous heat conduction equation in a general case.…”