We present experimental investigations, accompanied by numerical simulations on third harmonic generation microscopy at interfaces. In particular we study the variation of the emitted third harmonic intensity profile with the interface orientation. Our data confirm previous theoretical predications that only at interfaces perpendicular to the direction of the fundamental laser beam can the generated third harmonic profile exhibit a single spot in the forward direction. At interfaces parallel with the direction of the fundamental beam, the third harmonic intensity profile moves outside the forward direction and develops into a double-spot beam with a large opening angle. As an important consequence for implementations of harmonic generation microscopy, the numerical aperture of the double-spot third harmonic beam exceeds the numerical aperture of the fundamental beam.
© 2013 Optical Society of America
Original Manuscript: February 4, 2013
Revised Manuscript: April 24, 2013
Manuscript Accepted: May 4, 2013
Published: May 30, 2013
Vol. 8, Iss. 7 Virtual Journal for Biomedical Optics
Uwe Petzold, Christian Wenski, Alexander Romanenko, and Thomas Halfmann, "Spatial emission profiles at different interface orientations in third harmonic generation microscopy," J. Opt. Soc. Am. B 30, 1725-1731 (2013)