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In biomedicine, the mechanical properties of cells and tissues are increasingly recognized as indicator of pathological processes. Established measurement methods do not meet the requirements of biomedicine simultaneously: high spatial resolution, high throughput, non-contact, no markers and low measurement uncertainty. One particularly emerging technique, spontaneous Brillouin microscopy, enables optical three dimensional measurements with high spatial resolution. However, it suffers from low signal to noise ratio (SNR), which results in a long measurements duration. Impulsive stimulated Brillouin scattering (ISBS) is promising to overcome this shortcoming. In ISBS microscopy, an excitation takes place in the measurement volume through the superposition of two beams of an ultra-short pulsed laser. The resulting fringe pattern creates a standing acoustic wave in the sample. This standing wave can be probed with a continuous wave (cw) laser. The deflected part of the probe beam is amplitude modulated and can be measured by a photodiode. The determined center frequency is proportional to the sound velocity in the measurement volume and thus provides information on the local mechanical properties. For experiments, an ISBS microscope was built and characterized. Using this setup, measurements were carried out on the biological model material hydrogel. For the first time hydrogels of different stiffness could be discriminated. According to the requirements of biomedicine, the measurement volume has been reduced in size and thus a lateral resolution at cellular level was achieved. Based on an improved setup, investigations on the minimum measurement duration while satisfying the biomedical requirements mentioned above could be carried. The next steps are the transfer of the measurement technology to an application in biomedicine. A combination with other measurement techniques to a multimodal system might also be useful. In summary, Results obtained in our Research underline that ISBS microscopy offers an enormous potential for biomedical applications.
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