Fig. 4: Nonlinear optical properties of ITO/PFO/aluminum with applied voltages.

a Configuration of the SHG measurement. The TM-polarized FW is obliquely incident onto the ITO/PFO/aluminum device at an angle of 45°. L1 and L2 are lenses; LP1 and LP2 are polarizers. b Characterization of the spectral response of H-polarized SHG from ITO/PFO/aluminum with and without applied voltages. c The SHG intensity as a function of the applied voltages is plotted for the SHG wavelength at 420 nm. d The SHG intensity as a function of the applied voltages is plotted for the SHG wavelength at 405 nm. In the case of positive and negative voltages, the ITO layer serves as the anode and cathode, respectively. The fitting equations based on Eq. ( 1) are y = 0.4348x² − 1.1944x + 1.1512 for SHG at 420 nm and y = 0.1470x² − 3.7867x + 3.0622 for SHG at 405 nm. The retrieved relative values of the effective χ⁽²⁾ and χ⁽³⁾ of the EFISH device calculated from the fitting equations are 1.0729 and 0.6594 for SHG at 420 nm and 0.5543 and 0.3835 for SHG at 405 nm, respectively