Patent ID: 7230708
Filing Date: 2007-06-12
Classification: G01N

Abstract:
1. A method for photothermal examination of absorbing microheterogeneities in a sample by various external conditions, comprising: irradiating the sample observed by a focused pump laser beam and the wavelength coinciding with the absorption bands of the microheterogeneities examined, registering thermal effects and accompanied phenomena induced by the pump beam as a result of absorption in the sample, said phenomena including acoustic oscillations, secondary infrared radiation or thermal variations of the refraction index registered by measuring the parameters of the probe beam propagated through the same sample, the sample with the surface larger than the wavelength of the pump laser used is irradiated, said surface being of any required size, but not larger than the sample itself; the chosen probe beam diameter not being smaller than the pump beam diameter and not being larger than the sample, and spatial distribution of absorbing microheterogeneities in the irradiation volume being determined by simultaneous estimation of diffraction-limited phase distribution over the whole cross-section of the probe laser beam, said distribution being then transformed to an amplitude image using a phase contrast method; determining the size of single microheterogeneities larger than the pump laser wavelength is performed using analysis of spatial structure of said amplitude image; determining the average size of the microheterogeneities smaller than the wavelength is performed indirectly, by the characteristic time of cooling connected with said size, on the basis of the dynamics change analysis of the diffraction-limited amplitude images of said microheterogeneities by registering said microheterogeneities either at various moments of time beginning immediately after the pump irradiation is over, the chosen duration of said irradiation not being longer than the characteristic time of cooling of the microheterogeneity observed, or by registering the time phase of the probe beam as related to the intensity-modulated time phase of the pump beam.