A novel method for spatially-resolved thermal conductivity measurement by super-resolution photo-activated infrared imaging

A non-destructive thermographic procedure for the estimation of mechanical properties in steel through thermal diffusivity measurements

“…In fact, it has been demonstrated that as hardness increases, there is a corresponding reduction in thermal diffusivity [18,[33][34][35][36][37]. Among several methods present in literature for the non-destructive measurement of thermal diffusivity by thermography, using different sources, configurations and heating modes [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]45,46], the pulsed laser spot method in reflection mode has been used [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]45]. This method is based on the solution of the heat equation in the case of Gaussian distribution of energy, in adiabatic conditions, in a finite body after a Dirac pulse heating which is reported below:…”

“…Significant advantages can be obtained using non-destructive techniques (NDT), which can provide a check without influencing the component. Among all the NDT, active thermography has been proven to be effective for defects detections in composites and metals [7][8][9][10][11], process monitoring [12][13][14][15], thermophysical properties measurements [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] overcoming the limits of the traditional controls, because of a full field and no contact evaluation; thus 100% check is possible with a test duration compatible with high volume productions. Several past research works presented an anti-correlation between the hardness and thermal diffusivity [18,[33][34][35][36][37] and a thermographic procedure to evaluate the effectiveness of heat treatment in boron steel has been previously proposed [38,39] based on the use of spot pulsed laser method [19,21,24,[40][41][42].…”

Super‐Resolution Photothermal Imaging at the Microscale by Model‐Based Image Reconstruction

“…[25] The approximations simplify the theoretical treatment but guarantee wide applicability, covering any sample thickness of practical relevance. [24] In the case of thermally thin sample (Biot's number hL=k ( 1) and of infinitely thick sample (L ! þ∞), [25] respectively, the local surface temperature T x, y, z ¼ 0, t ð Þsolving Equation ( 2)-( 4) can be derived [25] as…”

“…Bearing in mind that we aim at detecting laser-primed temperature increments by an IR thermal camera, the continuous temperature profile T x, y, 0, t ð Þpredicted on the sample plane has to be spatially convoluted with the Gaussian-shaped camera point spread function and discretized over square pixels of side l equal to the camera pixel size [24] (Figure S1, Supporting Information). At time t, the i, j ð Þ-th pixel in the thermal camera images senses, therefore, a PSF-convoluted and pixel-averaged temperature increment ΔT LR i, j, t ð Þ(i ¼ 1 : : : N TC x , j ¼ 1 : : : N TC y ), which can be explicitly computed as…”

“…The same samples have been exploited previously by our group for the experimental validation of localization-based SR imaging [9] as well as for the experimental demonstration of novel quantitative thermal conductivity mapping protocols. [24] An ink pattern mimicking the acronym LABS (Laboratory of Advanced Bio-Spectroscopy) (Figure 2a) has been imaged at first. (f) The excitation beam, focused to a 28 μm waist, has been raster scanned across the sample with 50 ms dwell time τ on and 22 μm pixel size Δx.…”