There is a comprehensive review article in this month's Nature Photonics concerning many of the technological capabilities and recent advancements of multiphoton microscopy (MPM). The article details many recent advances in MPM engineering for achieving faster image acquistion, increased signal-to-noise ratios, and deeper imaging capabilities.
These advances are impressive and lead me to believe that MPM has become a rather mature technology. I'm curious to know to what extent biologists have used MPM to solve problems in their research since the review article is somewhat lacking in references that come from journals outside of physics and optics.
This is the same problem I encounter again and again in optics. It's very difficult to identify worthwhile work in a research field that primarily develops tools for researchers from other fields to use. I do not blame the optical scientists for this difficulty, though, and here's why. An optical sensing technique is usually not suited for publication in pure biology journals, so they must publish in optics and applied science journals. In this arena, they must argue for their technique relative to other related techniques, not to the suitability of their work for solving biological problems. A sentence in the introduction and conclusion of an article is usually sufficient for reviewers to acknowledge the technique's worth towards a biological problem of interest.