The invention of the confocal microscope by M. Minsky provided scientists a powerful tool for research on microscopic structures. This non-destructive method, including the advantages of superior optical resolution and the possibility of three dimensional imaging, is a key technology to many questions, especially in biology.
The spatial recording of a microscopic object in a transparent medium has to date only been possible in conventional laser scanning microscopes (LSM) by detecting the light emitted by the sample, e.g. the fluorescence or raman scattering.
By developing a microscope setup for sensing the transient absorption of very low dye concentrations (down to the single molecule level)[1], we achieved the possibility of sensing the spatial distribution of the dye concentration.
The "direct Confocal Absorption Microscope" (dCAM) [2] is, by contrast, a method which does not require any fluorescent dyes, e.g. the objects' self-absorption can be directly used. By exciting a microscopic sample with a focussed laser beam of a specific wavelength, its transmission changes to a certain degree in a specific volume element. This change in transmission is detected via a second laser beam and evaluated electronically. In other cases, any (photo-) physical processes can be analysed directly, e.g. the triplet-triplet-state absorption or the bleaching of the ground state in dependence of the measurement wavelength.
The dCAM-method can be applied to all scenarios where fluorescent dyes disturb three-dimensional structure determination (e.g. in living cells or in transparent polymers).

Advantages
· No dyeing of the sample required
· No contamination through toxic fluorescent dyes
· Use of non-fluorescent dyes
· Improved colour channel separation when several chromophores are present
· direct 3D recording of biological samples
· Homogeneity measuring inside of technical materials, e.g. polymers of wafers

[1] R. Bornemann, „Die Detektion einzelner Moleküle anhand ihrer Absorption“, Diploma Thesis, Universität Siegen 1998.
[2] German Patent No. DE 102 31 543