Photothermal radiometry methods in materials science and applied chemical research

Abstract

In this Review, the main techniques of the photothermal radiometry family with their varieties (modulated and pulsed photothermal radiometry and infrared photocarrier radiometry) and related methods (infrared thermography) are considered from the viewpoints of their specific features and application in chemical research and related disciplines. The basics of the methods and their technical implementation are briefly described. The focus of the paper is to examine the possibilities of photothermal radiometry methods—as techniques combining molecular spectroscopy and thermal characterization—physical and analytical chemistry, materials sciences, and biomedical research. The Review discusses the techniques of photothermal radiometry that find their applications in the various fields of the materials science like investigation of the thermal and structural properties of materials, defectoscopy, and dynamics of thermal processes. It also discusses the techniques that are used in the applied chemical research, in the evaluation of the optical properties at molecular or substance levels and the assessment of various substances including biomaterials. The outlooks of the further development in this area are briefly discussed.

Recent Progress in Modulated Photothermal Radiometry

“…The accuracy of these results has also been validated using a variety of other techniques, such as time-domain thermoreflectance [ 49 ] and deflection spectroscopy [ 48 ]. While these differing experimental designs produce similar results, some argue that the non-standardized apparatus design makes any comparisons inconclusive [ 45 ]. Other concerns, such as the lack of standard samples and uncertainty in the analysis, have started to be addressed [ 33 , 37 , 48 , 66 , 75 ].…”

“…Apart from directly modulating the laser drive current, the beam intensity can be externally modulated [ 42 ]. Acousto-optic modulators (AOM) and optomechanical choppers are forms of external modulation which are often used [ 19 , 28 , 43 , 44 , 45 ]. In AOM, the output intensity is proportional to an electric signal voltage through piezo-electric-induced diffraction [ 46 ].…”

“…Typically, the SNR of the recorded thermal signal is small, making direct analysis difficult; thus, signal processing techniques are needed to extract the required information for analysis [ 45 ]. Common among most MPTR implementations [ 28 , 45 ] is the use of lock-in amplifiers for signal processing. Lock-in amplification is a homodyne detection technique that modulates an input signal at frequency with a reference signal at frequency .…”

Pulsed Photothermal Radiometric Depth Profiling of Bruises by 532 nm and 1064 nm Lasers

“…However, these techniques are not sensitive to the chromophore depth distribution, as scattered light from many tissue layers is collected and analyzed indiscriminately. An attractive alternative is pulsed photothermal radiometry (PPTR), which has sufficient penetration depth and the ability to determine the depth distribution of chromophores [ 17 , 18 , 19 , 20 , 21 ]. In PPTR, we specifically measure transient changes in mid-infrared emissions from the sample surface after exposure to a short-light pulse; these signals are then used to noninvasively assess irradiation-induced temperature–depth profiles to reveal the depths of absorbing structures [ 22 , 23 ].…”

Measuring Thermal Diffusivity of Azoheteroarene Thin Layers by Photothermal Beam Deflection and Photothermal Lens Methods

“…Photothermal techniques, in essence, rely on the creation of temperature gradients within the material and its immediate environment, which are closely related to the fundamental thermal properties of the samples, encompassing thermal conductivity, thermal diffusivity, and thermal boundary resistance. The main advantages of photothermal techniques are their contactless nature, localized heating, as well as high sensitivity and accuracy due to the direct measurement of the deposited heat that the optical absorption causes on the sample [ 1 , 2 , 3 , 4 , 5 ]. The photothermal effect depends on the opto-thermal properties of the sample under examination.…”