Figure 1.
The effect of aberrations on image quality. (a) An aberration-free wavefront leads to a diffraction-limited focal spot in a point-scanning (e.g. two-photon fluorescence) microscope. (b) Specimen refractive index mismatches distort the wavefront of the excitation light, leading to a dim, enlarged focus. (c) Optimal imaging performance can be recovered by pre-shaping the wavefront of the excitation light to cancel out the specimen-induced aberration. The sinusoidal curves denote the phase relationship among the rays. Axial images obtained from two-photon excitation of 1-µm fluorescent red beads are shown for three different cases: (a) ideal, aberration-free imaging conditions, (b) an artificial aberration is introduced, causing a 8.6-fold decrease in brightness and a degradation of axial resolution, and (c) adaptive optics is used to recover ideal imaging performance.