Spatially Enhancing Resolution of Electric Field Induced Second Harmonic (SEEFISH) Generation Measurements

The spatial resolution of the ps Electric Field Induced Second Harmonic (EFISH) generation has been enhanced by using a non-collinear laser beam phase matching geometry. This approach is similar to the one used in Unstable Resonator – Enhanced Detection Coherent Anti-Stokes Raman Scattering (USED CARS). Briefly, the pump laser beam (1064 nm, pulse duration 150 ps, pulse energy 20-35 mJ) is separated into two coaxial beams before the focusing lens. The two beams, with the combined pulse energy of 10-18 mJ, overlap only near the focal point, generating the Spatially Enhanced EFISH (SEEFISH) signal over a significantly shorter region. Blocking of either of the two beams results in a complete suppression of the signal, demonstrating that it is generated by the superposition of the two beams overlapping near the focal point. Measurements of a known Laplacian field generated between two parallel cylinder electrodes in ambient air demonstrated that SEEFISH improves the spatial resolution of the measurements by over a factor of 2. The spatial resolution is improved further by reducing the focal distance of the lens. As expected, the magnitude of the SEEFISH signal is lower compared to that of the “conventional” EFISH, by a factor of 2-10, depending on the lens focal distance.