Polar structure in a ferroelectric bent-core mesogen as studied by second-harmonic generation

Area of Science:

• Nonlinear Optics
• Materials Science
• Condensed Matter Physics

Background:

• Ferroelectric liquid crystals (FLCs) exhibit spontaneous electric polarization.
• Bent-core molecules offer unique mesophases with potential for nonlinear optical applications.
• Chiral molecules introduce specific symmetry properties crucial for optical phenomena.

Purpose of the Study:

• To investigate second-harmonic generation (SHG) in a chiral bent-core ferroelectric liquid crystal (FLC).
• To determine the nonlinear optical coefficients and molecular hyperpolarizability.
• To confirm the ferroelectric uniform structure and its influence on optical properties.

Main Methods:

• Second-harmonic generation (SHG) measurements on well-aligned ferroelectric liquid crystal cells.
• Application of an electric field to achieve molecular alignment.
• Analysis of in-plane anisotropy of SHG signals under varying polarization conditions.
• Determination of nonlinear susceptibility tensor components (d coefficients).

Main Results:

• Observed two- or four-leaf patterns in SHG anisotropy, indicating a ferroelectric uniform structure.
• Determined nonlinear susceptibility tensor components: d(333) = 14.4 pm/V and d(311) = 49.2 pm/V.
• Calculated molecular hyperpolarizability tensor components: beta(zzz) = 14.5 x 10(-30) esu and beta(zxx) = 67.6 x 10(-30) esu.

Conclusions:

• The study successfully characterized the nonlinear optical properties of a chiral bent-core FLC.
• The determined molecular hyperpolarizability values align with those of achiral counterparts.
• These findings highlight the potential of chiral bent-core FLCs for advanced optical applications.