Figure 1
From: In vivo sub-femtoliter resolution photoacoustic microscopy with higher frame rates
Comparisons between PAM and 2PAM.
(a) In common PAM based on visible laser excitation process, temporal or spatial filtering is necessary to eliminate induced background and acquire the axial resolution. However, in 2PAM, with NIR excitation, only photons within the focal spot generate nonlinear photoacoustic signals. Therefore, intrinsic optical confinement determines the 3D spatial resolution. (b) Only mechanical scanning is applicable in current common PAM due to the small acoustic detection FOV. In contrast, 2PAM could be operated at low acoustic frequency creating large acoustic detection FOV. Optical scanning is thus possible.
