Wang Gui-Ying

Imaging properties of coherent anti-Stokes Raman scattering microscope

The coherent anti-Stokes Raman scattering (CARS) microscope with the combination of confocal and CARS techniques is a remarkable alternative for imaging chemical or biological specimens that neither fluoresce nor tolerate labelling. CARS is a nonlinear optical process, the imaging properties of CARS microscopy will be very different from the conventional confocal microscope. In this paper, the intensity distribution and the polarization property of the optical field near the focus was calculated. By using the Green function, the precise analytic solution to the wave equation of a Hertzian dipole source was obtained. We found that the intensity distributions vary considerably with the different experimental configurations and the different specimen shapes. So the conventional description of microscope (e.g. the point spread function) will fail to describe the imaging properties of the CARS microscope.

Factors in Design of Optical Super-Resolving Filters

Three key factors in design of optical pupil filters with super-resolving are studied. For the same normalized spot size, the factor of sidelobe intensity is more important for designing filters in applications. Thus the phase-only filters do not always perform better than the transmittance filters which always have lower Strehl ratio. The drawback of lower central core intensity can be compensated for by the high power laser. The argument has been justified in our numerical experimental results with the simplest filter patterns.

A New Method for Determining Dipole Moment Orientation of Single Molecules

A new imaging method is proposed to determine the three-dimensional dipole moment orientation of single fluorophore. Far-field microscopy can provide orientational information projected in the sample plane, while total internal reflection fluorescence microscopy (TIRFM) can offer the knowledge perpendicular to the surface because longitudinal electric-field components can be generated in total internal reflection geometry. By comparing fluorescence intensities measured with far-field epi-fluorescence microscopy and TIRFM, the exact information of single-fluorescent-molecule orientation is extracted. Detailed analysis of the method is given with a numerical example.