Alternating beam method /ABM/ in photothermal microscopy /PTM/ and photoacoustic microscopy /PAM/

The differential alternating beam method, used to measure small variations with the detector operating as a null detector, is reported. Applied to measure the thickness of plasma-sprayed coatings, the method was devised when small differences difficult to resolve were found in measuring thermal properties of nearly uniform spaces. Using plasma-sprayed tungsten-carbide coatings on stainless steel plates as samples, three thicknesses of coatings were made, using one coating as a reference sample. The results may have potential value in industrial applications, such as quality control; the ABM can also be used inside a photoacoustic cell.