Pulse Compression For Ultrafast Nonlinear Microscopy

It has been established that optical techniques based on nonlinear processes, such as two‐photon excited fluorescence (TPEF) and second harmonic generation (SHG), are advantageous for microscopic imaging at depth [1‐4]. When compared with confocal or wide‐field microscopy techniques, they provide greater penetration depths and superior image contrast. The nonlinear optical response to a focused laser field is intrinsically confined to the focal volume, which helps mitigating light scattering effects and allows imaging at depths as large as four‐five mean free path lengths [5‐7]. Longer wavelength of the excitation light (usually, in near‐IR domain) is also beneficial for dealing with scattering in tissues.