Nonlinear Confocal Microscopy for High-Resolution Measurement

We demonstrate cell imaging with a new confocal nonlinear optical microscope using a low-power cw laser. The confocal nonlinear optical microscope, employing degenerate four-wave mixing geometry, can detect the fine structure of submicron objects with nanoscale contents such as biological cells. The optical signal, which is given by the third-order susceptibility tensor, is confined to the focal region of the focusing incident beam, because the absorption of the object is dependent on the third power of the excitation laser intensity. We have observed a thylakoid membrane in a chloroplast by scanning the tensor element inside.