Depth-encoded spectral domain phase microscopy for simultaneous multisite nanoscale optical measurements of nerve activation

Spectral Domain Phase Microscopy (SDPM) is a recent extension of Spectral Domain Optical Coherence Tomography (SDOCT) that exploits the extraordinary phase stability of spectrometer-based systems with common-path geometry to resolve sub-wavelength displacements within a sample volume. This technique has been implemented for high resolution axial displacement and velocity measurements in biological samples, but since axial displacement information is acquired serially, has been unable to measure fast temporal dynamics in extended samples. Depth-Encoded SDPM (DESDPM) uses multiple sample arms with unevenly spaced common path reference reflectors to multiplex independent SDPM signals from separate lateral positions on a sample simultaneously using a single interferometer, thus limiting the time required to detect unique optical events to the integration time of the detector. The minimum measured sample displacements determined from the standard deviation of the detected phase as a function of time two ideal reflectors were 407 and 730 pm. Heat-induced expansion in a microscope slide was measured at two sites simultaneously. A 51 ms delay in 50% rise time of the surface displacement was measured. Further application of this technique to biological samples could yield insight into temporal dynamics of activation signals.