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Between 1965 and 1980 basic research into the medical use of lasers led to the discovery of new applications. Today we differentiate between three classes of principle interactions. Firstly there are the photochemical effects whereby laser energy is used to trigger off photochemical reactions on biomolecules by absorption of either natural or artificial dyes, or chromophoric groups. This is one of the basic principles of nature, e.g. photosynthesis and the vision process. —A further effect is based on the fact that the absorption of light at a suitable wavelength and intensity is converted into heat which accordingly leads to a heating effect of the irradiated tissue. It is a thermal effect whereby the result is dependent on the degree of absorption and the amount of radiation absorbed. In this way photocoagulation and tissue cutting is possible. —The third effect can be summarized under the term “non-linear effects”, as they cannot be explained by the linear absorption of photons, i.e. radiation, and therefore are classified according to the effects that they produce. It is possible by these non-linear effects to remove material fragments from the surface by light without heating the surrounding area. —Between the above mentioned thermal effects, there are the so-called “photoacoustic effects”. Thermal absorption and time behaviour of the light radiation leads to changes in the acoustic and thermal density which results in the destruction of material. —The laser may contribute in future to solving the following problems: Recanalisation of arterial blood vessels; Destruction or fragmentation of stones in the kidneys, bladder, efferent urinary tracts as well as in the bilary tract; photochemical reactions by choosing the applicable laser wavelength, e.g. polymerisation of biocompatible plastics “in situ”. |
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