Second-order optical coherence tomography: Deeper and turbulence-free imaging

The superior resolution of optical coherence tomography (OCT) with respect to alternative imaging modalities makes it highly attractive, and some of its applications are already in extensive clinical use. However, one of the major limitations of OCT is that the tomographic picture it generates is depth-limited to approximately 1 mm in most biological tissues. This is mainly due to the spatially turbulent nature of the tissue, which leads to scattering. Moreover, this technique is extremely sensitive to temporal variations in the medium. We show that insensitivity to temporal and spatial turbulence may be gained by replacing the linear detector with an ultrasensitive two-photon detector. These results have striking implications on the attainable penetration depth of optical imaging and on its sensitivity to sample motion.