A side-chain liquid crystalline copolymer containing
ether−nitrobiphenyl groups was
investigated as a nonlinear optical material. Ultrathin films have
shown second harmonic generation
and therefore have a variety of interesting applications.
Waveguides composed of multilayers of the
copolymer have been fabricated, and propagation losses as low as 2.3
dB/cm in a lowest order TE mode
at 800 nm wavelength have been measured. The second harmonic
coefficient is d
33 = 42.0 ± 1.7
pm/V
at the 1064 nm fundamental wavelength and is consistent with an
oriented gas model. From spectroscopic
ellipsometry measurements the film refractive index is 2.24 ± 0.15
and the extinction coefficient ≤0.05
in the visible range of wavelengths. The monolayer and multilayer
repeat structures were also studied
by X-ray reflectivity and diffraction. The optical thickness and
the oscillations in the reflectivity were in
reasonable accord with a repeat length of about 3.6 nm.
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