Enhanced resolution in two-photon imaging using a TM01 laser beam at a dielectric interface

We have experimentally demonstrated that the resolution of a commercial two-photon microscope is improved using a TM01 laser beam. With a water immersion objective having a 1.2 NA, the measured point-spread function has an area of 0.15 lambda(2). We used a plane interface between dielectrics instead of an annular aperture to increase the relative contribution of the longitudinal field of the TM01 laser beam. The results are in agreement with the vectorial diffraction theory established by Richards and Wolf [Proc. R. Soc. Lond. A 253, 358 (1959)]. The TM01 laser beam was produced with a quadrant of half-wave plates. We have also used the same mode converter to generate a TE01 laser beam with a zero at the beam center. (C) 2009 Optical Society of America