Inversion of microscopic lock-in thermograms in the presence of emissivity contrast

None of the conventionally displayed images of lock-in thermography (in-phase or 0° image, out of phase or -90° image, amplitude image, phase image) is able to become inverted in the presence of emissivity contrast. The phase signal is inherently emissivity-corrected, but here contributions of different heat sources superimpose very nonlinearly, which prevents any meaningful deconvolution. It is shown that the "0°/-90°" image, as an alternative kind of representation of lock-in thermography images, being also inherently emissivity-corrected, is able to be inverted for obtaining e.g. the lateral power distribution in an electronic device. Blackening the surface by colloidal bismuth also may remove the emissivity contrast.