Principle
The cutting process is performed by a femtosecond laser, emitting radiation in the near-infrared range. Within this wavelength range, the laser is able to penetrate the tissue up to a certain depth without causing thermal damage. By tight focussing the laser radiation, intensities over 1 TW/cm2 (1 TW = 1012 watts) arise inside the laser focus. These extreme intensities induce nonlinear effects and optical breakdown occurs. This causes the disruption of the material, limited to the focal point. The process is known as photodisruption.
Due to the ultra short pulse duration of only a few femtoseconds (1 fs = 10−15 seconds) there is only very low energy of a few nanojoules (1 nJ = 10−9 joules) per laser pulse deposits into the tissue. This limits the interaction range to diameters below one micrometer (1 μm = 10−6 meters). Out of this range there is no thermal damage.
Moved by a fast scanner, the laser beam writes a cutting plane into the sample. A positioning unit moves the sample simultaneously, so that the sample can be processed within a short time.
Read more about this topic: Laser Microtome
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