Method and apparatus for thermoacoustic or thermal wave microscopy to detect surface and subsurface information from a material on a microscopic scale. A thermal wave is generated in a material by causing periodic, localized heating at a microscopic spot by focusing intensity modulated light, or electromagnetic...http://www.google.es/patents/US4255971?utm_source=gb-gplus-sharePatente US4255971 - Thermoacoustic microscopy
