Systems and methods are provided for detecting the flow of blood or other fluids in biological tissue by illuminating the biological tissue with two or more beams of coherent light and detecting responsively emitted light. A difference in wavelength, coherence length, beam divergence, or some other property of the beams of illumination causes the beams to preferentially scatter from, be absorbed by, or otherwise interact with respective elements of the biological tissue. Flow properties in one or more regions of the biological tissue (e.g., a region with which both beams of light preferentially interact, a region with which only one of the beams preferentially interacts) could be determined based on detected responsively emitted light from the biological tissue. Variations in speckle patterns over time and/or space, Doppler shifts, or some other properties of the detected light could be used to determine the flow properties.
