After 200 years from the discovery of heat equation by the Fourier, we notice that the subject is still new. The crux of mystery is the much elaborated mathematical techniques which were developed during last century. In the case of Newton models was the applicability of group theory, but for the heat transfer theory we applied the integral transform technique. The integral transform technique is used in "combination" with Laplace transform. The method was developed from mathematical point of view in the early 60', but only in the last decade was used with success in laser processing. The book presents a large set of applications: from classical physics to quantum physics trends in laser processing. A parallel between the integral transform technique and Green function is also made.