Nonlinear optical microscopy

The research project deals with applications of nonlinear optical microscopy, e.g. to investigate transparent samples in biology or engineering (e.g., in material diagnostics).  As it is the nature of transparent media, they are not accessible by conventional microscopy. Alternative methods (e.g. phase contrast and differential interference microscopy) exploit the differences in refractive indexes of different transparent media. However, due to rather small variations of the refractive indexes in different transparent media, the obtained contrast in these common techniques is small. Nonlinear microscopy exploits nonlinear optical properties, which vary significantly even in different transparent media. This allows for imaging with high contrast.

In our setup for nonlinear optical microscopy we use frequency conversion processes (e.g. second and third harmonic generation (SHG and THG)), driven by ultra-short laser pulses to image transparent samples in three dimensions. The laser focus is scanned across and through the sample. The efficiencies of SHG and THG are monitored to obtain a 3D image, in particular indicating interfaces between different media in the same sample. The technique enables investigation of any kind of transparent media in every condition of aggregation without the need for labeling or tracers. We investigate the basic physics of harmonic generation in tightly focused laser beams, which often yields surprising features compared to simple expectations from paraxial optics (which is no valid assumption here anymore). Moreover, we develop new variants of harmonic generation microscopy (e.g. based on variations of optical properties near resonances) and transfer the techniques to new fields of applications (e.g. microfluidics).

References

[4] Dispersion-enhanced third-harmonic microscopy
C. Stock, K. Zlatanov, T. Halfmann
Opt. Commun. 393, 289 (2017)
Opens external link in new windowDOI:10.1016/j.optcom.2017.02.059

[3] Spatial emission profiles at different interface orientations in third harmonic generation microscopy
U. Petzold, C.Wenski, A. Romanenko, and T. Halfmann
J. Opt. Soc. Am. B 30, 1725 (2013)
Opens external link in new windowhttp://dx.doi.org/10.1364/JOSAB.30.001725

[2] Imaging diffusion in a microfluidic device by third harmonic microscopy
U. Petzold, A. Büchel, S. Hardt, and T. Halfmann
Exp. Fluids 53, 777 (2012)
Opens external link in new windowhttp://dx.doi.org/10.1007/s00348-012-1321-5

[1] Effects of laser polarization and interface orientation in harmonic generation microscopy
U. Petzold, A. Büchel and T. Halfmann
Opt. Expr. 20, 3654 (2012) 
Opens external link in new windowhttp://dx.doi.org/10.1364/OE.20.003654

Contact

Prof. Dr. Thomas Halfmann
Nichtlineare Optik/Quantenoptik
Institut für Angewandte Physik
Fachbereich 05 - Physik
Technische Universität Darmstadt
Hochschulstr. 6
D-64289 Darmstadt

+49 6151 16-20740

+49 6151 16-20741 (Sekretariat)

+49 6151 16-20327

thomas.halfmann@physik.tu-...

T. Halfmann on ResearcherID

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