
1353D SHG Imaging and Analysis of Fibrillar Collagen Organization
the focused spot is comparable or larger to 1/Δk
1
, that is, the material coherence length based on disper-
sion. is condition is valid for image acquisition performed at medium NA.
Forward SHG will be dominated by phasematching with smaller Δk
f
values for domains on the order
of L
c
= 2
π
/Δk
f
, corresponding to small K
f
values. Although the overall forward SHG signal is a sum-
mation of all the Δk terms, the lower Δk terms will dominate due to their relatively high conversion
eciency (see Figure 6.2b). us, we associate forward SHG primarily with Δk
1
(i.e., the maximum
coherence ...