Optical Setup for Investigating the Hyperpolarizability of Organic Nanostructure Materials in Solutions Using Electric Field Induced Second Harmonic Generation

Abstract

In this paper, an optical setup for electric field-induced second-harmonic generation (EFISH) at 1.9 μm experiment was arranged and used to investigate and determine the hyperpolarizability of some nanostructure organic components in two different solutions. First, a laser beam at 1.9 μm was generated by pumping a hydrogen Raman cell pressurized to 55 bar with 10 Hz Q-switched Nd: YAG nanosecond laser operating at λ = 1.064 μm. Next, the generated laser beam was aligned with all optical components within the assembly. The final step was to optimize the beam’s power and polarization at the center of the EFSH cell. Different nanostructure organic samples in solutions were prepared with nearly the same standard concentration of about 5 mmol/L to be investigated under the optimized system. Two solvents were used in this work, dichloromethane, or DCM (CH2Cl2), and chloroform, or trichloromethane (CHCl3). First, the harmonic order hyperpolarizability of five organic molecules in solutions with different chemical components such as quinolinium groups and organic boron complexes (supplied by the Chemistry Department at Catania University, Italy) were experimentally investigated experimentally. Only component (2-(2-[5′-(N,N-dimethylamino)-(2,2′-bithiophen)-5-yl]vinyl)-1-methyquinolin-1-ium iodide) in chloroform showed a significant difference in Maker fringes amplitude of the applied electrical field in comparison with fringes of its pure solvent. The value of μb for this component has been calculated as 1320 x 10-48 esu. This value indicates that the component is a suitable candidate for use in second-harmonic generation imaging for biological applications.