Pulsed-Laser Time-Resolved Thermal Mirror Technique in Low-Absorbance Homogeneous Linear Elastic Materials

Abstract

A theoretical model for a time-resolved photothermal mirror technique using pulsed-laser excitation was developed for low absorption samples. Analytical solutions to the temperature and thermoelastic deformation equations are found for three characteristic pulse profiles and are compared to finite element analysis methods results for finite samples. An analytical expression for the intensity of the center of a continuous probe laser at the detector plane is derived using the Fresnel diffraction theory, which allows modeling of experimental results. Experiments are performed in optical glasses, and the models are fitted to the data. The parameters of the fit are in good agreement with previous literature data for absorption, thermal diffusion, and thermal expansion of the materials tested. The combined modeling and experimental techniques are shown to be useful for quantitative determination of the physical properties of low absorption homogeneous linear elastic material samples.

Unravelling the effects of radiation forces in water

“…The PM method has been used to detect surface displacement of a few nanometres in solids2425262728. One laser irradiates the sample normal to its surface and a low-irradiance laser probes the deformation of the sample by measuring the on-axis intensity variation of the central portion of the probe beam reflected off of the sample surface; the expansion/contraction of the sample diverges/converges the probe beam at the detector, diminishing/increasing the signal at the detector.…”

Laser induced thermoelastic surface displacement in solids detected simultaneously by photothermal mirror and interferometry

“…This term can be neglected [22] as the signal oscillations due to the inertia term are not observed experimentally considering the relatively long detector response time [23]. The z-component (normal) of the displacement vector at the sample surface for a semi-infinite sample is [8] and λ p is the probe beam wavelength. The normal surface deformation given by Eq.…”

“…The photothermal mirror (TM) spectrometry detects the deformation of the illuminated surface by analyzing the focusing or defocusing of the reflected probe beam in the far field region [8][9][10][11][12]. TM measures a convoluted signal arising from the wavefront distortion caused by the probed surface of the sample in addition to the phase shift created by heat-coupling in the fluid surrounding the sample.…”

“…TM measures a convoluted signal arising from the wavefront distortion caused by the probed surface of the sample in addition to the phase shift created by heat-coupling in the fluid surrounding the sample. This method has been recently introduced under pulsed Gaussian laser excitation for the measurement of thermal diffusivity and thermo-optical properties of semi-transparent and opaque solids [8,9] and for the detection of thermoelastic waves launched by a localized heat deposition [13][14][15]. This method has also been used to detect surface displacements induced by radiation pressure at air-liquids interfaces [11,12].…”

Generation and detection of thermoelastic waves in metals by a photothermal mirror method

“…10 Detection of light-induced elastic waves is feasible with many different experimental approaches. [3][4][5][6][7][8][9][10][11][12][13][14][15] Bulk and surface waves can be detected utilizing capacitive, piezoelectric, electromagnetic, and optical transduction mechanisms. 16 The possibility of remote generation and stand-off detection of elastic waves using optical probes makes photothermal methods attractive for material characterization 15 and non-destructive testing.…”