Imaging with Phase- Sensitive Narrowband Nonlinear Microscopy

The signals generated in second harmonic generation (SHG) microscopy, third harmonic generation (THG) microscopy, and coherent anti-Stokes Raman scattering (CARS) microscopy are coherent. This implies that the oscillators in the focal volume, set in motion by the driving fields, radiate with a well-defined phase. In other words, there is a clear phase relationship between the waves that are emitted from the focal region. Because of this relationship, the resultant waves will interfere. The

I. The Importance of Phase .............................................................................. 213 II. Coherent Signals from Tight Focal Volumes ................................................ 216

A. The Tightly Focused Field ..................................................................... 216 B. Nonlinear Excitation at the Focus ......................................................... 218

III. Interferometric Nonlinear Microscopy .........................................................220 A. Why Interferometry Is Useful ...............................................................220 B. Nonlinear Interferometry and Spectral Resonances ............................. 222 C. Interference in Focus .............................................................................224 D. Interferometric Imaging ........................................................................226