THG (Third Harmonics Generation) is an intrinsic effect of matter. Combining THG with microscopy creates a powerful tool of imaging

• No dyes neccessary, no bleaching, no physiological changes and cell death
• Blue shifted signal, no spectral congestion with auto fluorescenc
• High spatial resolution due to multi-photon character of interaction

Examples show Third Harmonics Generation images courtesy of Prof. Michiel Mueller, University Amsterdam recorded with a High Q Laser femtoTRAIN Nd:Glass laser system

THG optical sections of a polystyrene bead in a nematic LC medium near the equatorial plane. The input polarization is phi=0 for (a) and phi=pi/2 for (b).
from: R. S. Pillai, M. Oh-e, H. Yokoyama, G. J. Brakenhoff and M. Mueller, "Imaging colloidal particle induced topological defects in a nematic liquid crystal using third harmonic generation microscopy," Optics Express 14(26), 12976-12983 (2006)

THG images of lipid droplets in HeLa cells. (a) and (b) are two optical sections axially separated by 1.5 mu. (c) is the wide field transmission image of approximately the same region. (d) and (e) represent high resolution images of the lower part of the images (a) and (b) respectively. Imaging conditions: objective: 40x, 1.3 NA oil immersion; laser power <10 mW; acquisition time 80 ms per pixel.

from: R. S. Sreedharanpillai, "Third-harmonic generation from isotropic and anisotropic media using focused beams," Thesis, University of Amsterdam (2007)