Submillisecond second harmonic holographic imaging of biological specimens in three dimensions.

Optical microscopy has played a critical role for discovery in biomedical sciences since Hooke's introduction of the compound microscope. Recent years have witnessed explosive growth in optical microscopy tools and techniques. Information in microscopy is garnered through contrast mechanisms, usually absorption, scattering, or phase shifts introduced by spatial structure in the sample. The emergence of nonlinear optical contrast mechanisms reveals new information from biological specimens. However, the intensity dependence of nonlinear interactions leads to weak signals, preventing the observation of high-speed dynamics in the 3D context of biological samples. Here, we show that for second harmonic generation imaging, we can increase the 3D volume imaging speed from sub-Hertz speeds to rates in excess of 1,500 volumes imaged per second. This transformational capability is possible by exploiting coherent scattering of second harmonic light from an entire specimen volume, enabling new observational capabilities in biological systems.