Adaptive Wavefront Correction in Two-photon Microscopy: Coherence-gated Wavefront Sensing

The focus of a two-photon microscope is often degraded by inhomogeneities in therefractive index within biological specimens. In this book it is shown for variousspecimens, even for living zebrafish, that the resolution and the fluorescence signal of atwo-photon microscope can be substantially improved by using adaptive optics, i. e. wavefront correction based on coherence-gated wavefront sensing (CGWS). The advantageof using CGWS relies on the fact that the wavefront distortions are sensed by backscatteredinstead of fluorescent light. Thus, neither photodamage nor photobleaching occurs andwavefront distortions can be sensed in less than 1 microsecond with an accuracy of lambda/50, even in strongly scattering samples. Furthermore, CGWS is thoroughly investigated for all relevant parameters affecting themeasurement process, such as coherence length, polarization of the light, density ofscatterers, and coherence-gate position. The book is mainly addressed to experts in the field of optical physics and light microscopy.