Figure 6: Scattering directions of SHG with Bessel beam excitation.
From: Efficient second-harmonic imaging of collagen in histological slides using Bessel beam excitation
(A) Phase-matching as a function of SHG scattering direction. (B) Top left, numerical simulations of SHG from a slab sample centered at focus as a function of sample thickness and emission direction. Off-axis emission increases with sample thickness in this range owing to good phase matching. Near-axis scattering efficiency oscillates with sample thickness. Bottom right, far-field emission diagrams for sample thicknesses of 3 μm and 6 μm. Right, integrated SHG as a function of sample thickness shown in linear and logarithmic scales, for different ranges of detection NAs: near-axis scattering (red), off-axis scattering (yellow), and total scattering (blue). Off-axis SHG scales as the square of sample thickness up to approximately 10 μm. Simulation conditions: λ = 1100 nm, NAB = 0.8 ± 0.1, n = 1.33, no dispersion. (C) SHG images of collagen fibers recorded with Bessel excitation (800 nm, NAB = 1) and angular filtering in the detection path. Signal was successively recorded with the following conditions (from left to right): detection in all angular directions with NAdet ranging from 0 to 1.2; detection of off-axis SHG with NAdet ranging from 0.6 to 1.2; detection of near-axis SHG with NAdet ranging from 0 to 0.2 and tripled acquisition time.
