Two-dimensional imaging of a second-order nonlinear optical process

Spatiotemporal imaging of sum-frequency generation process through second-order nonlinear optical interaction in a nonlinear crystal under femtosecond pulsed illumination is presented. Two focal points in the spatial dimension that result from use of widely separated wavelengths (780 and 1560 nm) including their appropriate intensity ratios are captured accurately, emphasizing the sensitivity and robustness of this detection scheme. Most importantly, cross-correlation width that is used as characteristic measure from such techniques remains constant at the two focal points. However, this highlights the critical role of nonlinear crystal position along beam propagation axis during such collinear intensity cross-correlation measurements involving different wavelengths.