Main fields of work

Our group studies the application of ultrashort laser pulses (approx. 100fs pulse duration) in biology and microscopy. If ultrashort laser pulses are tightly focused by high numerical objectives (NA>1), very high light intensities are achievable at the focus site, allowing imaging and manipulation of subcellular structures. Normally transparent materials become absorbing by the simultaneous absorption of several photons. This multiphoton absorption allows the excitation of dye molecules inside cellular samples. By detection of the fluorescent light with photomultipliers, very high sensitivity combined with very high resolution is possible.

The main advantages of the ultrashort laser pulses are, first, the high penetrations depth and, second, the broad spectrum. Because of its low absorption in biological samples, infrared laser light (800nm central wavelength) is ideal for imaging with high penetration depth. The broad spectrum offers the possibility to excite a large number of various dyes. If one uses considerably higher laser energies in the same setup, the high intensities at the focus region lead to generation of free electrons. Once a certain threshold is reached, these free electrons lead to a highly localized ablation within the bulk of the material. “Nanosurgery” inside even living cells becomes possible. In contrast to commonly used UV-laser or ps-laser systems, the applied energies are two to three orders of magnitude lower at the application of ultrashort laser pulses, allowing a precise manipulation of structures in the sub-micrometer range. Possible applications are in microscopy and cell manipulation, like gene transfer.

Our main goal is a better understanding of processes at the site of the laser interaction with the biological material. Using this understanding, we are trying to improve the imaging qualities and cutting resolutions of our systems.

More information

For more detailed information about the Biophotonics Group please visit www.lasermedizin.uni-hannover.de/index.php?id=biophotonik&L=1.