Scanning second harmonic microscopy techniques with monomode and near field optical fibers

Extending our scanning second harmonic microscopy (SSHM) technique for the detection of lateral orientational inhomogeneities in high field poled polymer films, we present results with considerably improved lateral resolution by using optical fiber technology. Two experimental setups for measuring the ${\chi }^{\text{(2)}}$ susceptibility of thin films are introduced. The first setup uses a standard monomode infrared-fiber with 10 μm core that carries the coherent fundamental infrared wave to the surface of a poled polymer film (illumination mode). The generated doubled frequency wave behind the nonlinear optical sample is detected by a photomultiplier tube. In the second setup a lens focuses the fundamental wave into the poled film. The resulting second harmonic wave is coupled into a 2.5 μm single mode fiber. SSHM micrographs of high field poled nonlinear optical polymer films were obtained with lateral resolutions of <3.5 μm. SSHM was also realized with a scanning near field optical microscopy fiber in pick up mode.