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Second-Harmonic Generation Imaging ofSelf-Assembled CollagenGels
is valid if the phase mismatch Δk and the index of refraction remain constant regardless of ber orienta-
tion. In fact, collagen’s birefringence of Δn ~ 0.003 (where n along the collagen monomer’s long axis > n
along the short axis) is assumed to be negligible. is seems a valid assumption since the calculation
is compared to an experimental SHG signal averaged over an ensemble of collagen bers only roughly
aligned. Furthermore, Δk may be assumed constant since the SHG interaction volume (roughly the
focal volume dimensions, ~200 nm lateral × 600 nm axial) is smaller than the mean ber diameter and
length in these cases, and can be assumed to be completely lled when c