William Angerer - Department of Physics and Astronomy - University ...

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parameter symbol value
surface density Ns 4x 10 14 cm- 2 [6]
hyperpolarizability
oP)
zzz
4 x 10- 30 esu [6]
effective beam area AeJJ 7 xlO- 11 cm 2
(area of nanotubes)
fundamental Fresnel factor Lxx(w) 1 [6]
second-harmonic Fresnel factor Lxx(2w) 1 [6]
Table 7.3: Properties of PNBA for calculating SHG from a PNBA film
we assume the second-harmonic signal from a film of aligned PNBA molecules results
solely from Q~;~.
The calculation of the nonlinear signal from a surface of aligned PNBA molecules
includes the parameters in Tables 7.1 and 7.3. This calculation is nearly identical
to the calculation of the hyperpolarizability of the carbon nanotubes. The distinction
between the calculations is that the nanotube calculation uses an SHG signal to
determine the hyperpolarizability, while the PNBA calculation assumes a hyperpolarizabiIity
to determine the SHG signal. vVe determined that "-' 1.8 x 10 4 SH photons
are generated from a PNBA film per second. This SHG response is substantially
greater than the SHG upper limit from carbon nanotubes (6 photons per second).
Thus! SHG microscopy can easily probe domains of nonlinear molecules. However.
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