TITLE:
Nonlinear Optical Properties of Two Different Nanoassemblies of Polydiacetylene (PDA): PDA Nanovesicles and PDA Nanocrystals
AUTHORS:
B. Bhushan, T. Kundu, B. P. Singh
KEYWORDS:
Third Order Nonlinear Optical Properties; Second Molecular Hyperpolarizability; Conjugated Polymers; Polydiacetylene
JOURNAL NAME:
Optics and Photonics Journal,
Vol.3 No.4,
August
8,
2013
ABSTRACT: We have synthesized and characterized two different
nanoassemblies of polydiacetylene (PDA), PDA nanovesicles and PDA nanocrystals,
in order to study the influence of chain packing geometry of the two
nanoassemblies on their third order nonlinear optical properties. The second
molecular hyperpolarizability γ(-ω,ω,-ω,ω）of the two samples was investigated by antiresonant ring
interferometric nonlinear spectroscopic (ARINS) technique using femtosecond modelocked
Ti:sapphire laser in the spectral range of 720 nm - 820 nm. The
observed spectral dispersion of γ has been explained in the framework of three-essential states model
involving the ground state, a one-photon excited state and a two-photon excited
state. The observed optical nonlinearity has been correlated with the electronic
structure of the two samples. The energy of two-photon state, transition dipole
moments and line width of the transitions have been estimated. Our studies show
that the arrangement of polymer chains in polydiacetylene nanocrystals is more
favorable for higher nonlinearity.