Stuttgart 2012 – wissenschaftliches Programm

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K: Fachverband Kurzzeitphysik

K 4: Poster I

K 4.5: Poster

Dienstag, 13. März 2012, 16:30–18:30, Poster.V

Applications and investigations of harmonic microscopy in microfluidics — •Uwe Petzold, Andreas Büchel, and Thomas Halfmann — Institut für Angewandte Physik, Technische Universität Darmstadt, Hochschulstraße 6, D-64289 Darmstadt, Germany

In recent years, second harmonic generation (SHG) and third harmonic generation (THG) microscopy advanced towards powerful tools for three-dimensional imaging of transparent biological samples. The basic concept of these techniques is to drive off-resonant frequency conversion processes in tightly focussed laser beams. The second and third harmonic appear only at interfaces, as the harmonics interfere destructivly in the bulk medium due to the Gouy phase shift. By scanning the laser focus across the sample, we obtain a three-dimensional image. In contrast to THG, SHG occurs only at interfaces of non-centrosymmetrical media. These features make harmonic generation microscopy a valuable instrument to image interfaces, even at the boundary of two transparent or even refractive index-matched species. We present systematic experimental investigations with regard to the effects of laser polarization and interface orientation in SHG and THG microscopy. Moreover, we demonstrate novel applications of harmonic microscopy also in the strongly expanding field of microfluidics. In particular, we apply third harmonic microscopy to image the flow of immiscible fluids and to characterize the near-surface mixing of miscible, transparent (or even index-matched) fluids. No labeling, staining or resonant excitation is required to obtain high-resolution images by harmonic microscopy.