The invention relates to optical
microscopy, and more particularly to the methods for photothermal examination of absorbing microheterogeneities using
laser radiation. The invention can be widely used in
laser technique, industry, and
biomedicine to examine transparent objects with absorbing submicron fragments, including detection of local impurities and defects in super-pure optical and semiconducting materials and non-destructive diagnostics of biological samples on cellular and subcellular levels.The object of the present invention is to increase sensitivity, spatial resolution and informative worth when examining local absorbing heterogeneities in transparent objects, as well as to detect the size of said heterogeneities even if said size is smaller than the
radiation wavelength used.Said object is achieved by the pump beam
irradiation of a sample, the duration of said
irradiation not being longer than the characteristic time of cooling of the microheterogeneity observed. A relatively vast surface of the sample is irradiated at once, the size of said surface not being larger than the
wavelength of the pump
laser used. The
refraction index thermal variations, induced by the pump beam in the sample and being the result of absorption, are registered by the parameter change of the probe laser beam. A chosen probe
beam diameter should not be smaller than the pump
beam diameter. The
diffraction-limited phase distribution over the probe laser beam cross-section is transformed to an amplitude image using a phase contrast method. The properties of microheterogeneities are estimated by measuring said amplitude image.