Figure 4.

Monte Carlo simulations are used to calculate the expected fluorescence distribution for an imaging depth of 400 μm in a sample with a 460-nm FWHM lateral spot size, τ_p = 270 fs, l_s = 80 μm, and g = 0.85. These parameters resulted in an R value of 1∕30. (a) shows the lateral and axial distribution of the circumferentially integrated background fluorescence distribution. In this case, most of the background fluorescence comes from above the imaging plane and within 200 μm of the optical axis. (b) shows the contributions from ballistic (B²), scattered (S²), and combined 2(B+S) photons separately. The total fluorescence generation per transverse slice is relatively constant through the first three l_s deep. The solid and dotted lines represent simulations with excitation pulse durations of 270 and 135 fs, respectively. (a) is normalized so that the maximum out-of-focus fluorescence is one, (b) is normalized so the maximum fluorescence is one.