
130
Second Harmonic Generation Imaging
sectioning, the incident photons are focused by an objective lens to an axial spot within the tissue
at depth z
f
, where the beam has a width or 1/e
2
radius of
ω
beam
using the experimental NA = 0.8. e
transmission of the laser, T
ω
, that reaches the focal depth z
f
is then determined based upon bulk
optical parameters at the fundamental wavelength, and the cone formed by the experimental NA.
is then accounts for the primary lter eect on laser intensity and determines the density of bal-
listic photons that arrive at the focus. To estimate the relative SHG brightness, that is,
χ
(2)
values of
the normal