Development of Apparatus for Simultaneous Measurement of Photocurrent and SHG

Many studies have been done investigating the second order nonlinear response of noncentrosymmetric materials to gain insight to the electronic structures of these materials. Photocurrent and optical second harmonic generation (SHG) are two second order nonlinear phenomena that share the same form of the second order nonlinear susceptibility tensor but are sensitive to distinct energy regimes of the electronic structure of the material under investigation. We present the development of an experimental apparatus for the simultaneous measurement of these two nonlinear phenomena using an ultrafast laser-based scanning approach. We show that the laser scanning provides a spatial resolution of these two nonlinear responses down to the optical diffraction limit, and the confocal imaging scheme adopted in our design assures a constant incident electric field over a wide scanning area. We also discuss our effort in enhancing these nonlinear responses, by compressing the laser pulse to its transform limit. Finally, we will discuss future opportunities brought by this apparatus, such as developing time resolved scanning nonlinear optical techniques.