混浊介质角域成像(ADI)实验中光传播时间门控和偏振优选效应
Angular Domain Imaging (ADI) employs an angular filter array to accept photons within a small acceptance anglealong the axis of an aligned laser light source and preferentially reject scattered light. Simulations show that theaccepted photons travel the shortest paths between source and detector and are therefore the earliest to arrive. Wefabricated angular filter arrays using silicon bulk micromachining and found that an array of 60 μ m square shape microtunnels1 cm in length accepted photons within 0.48 degree of axis of the micro-tunnels. This small acceptance anglerejected most of the scattered light and sub-millimeter resolution targets could be resolved in a few centimeters of turbidmedium with at least six times reduced mean free path. ADI through media with higher scattering coefficients was notachievable due to unwanted acceptance of late arriving scattered photons. To reject the late arriving photons, we addedtime-domain filtration and linear polarization to ADI. The implementation of a time-gated camera, a 780 nm femtosecondpulsed laser, and linear polarization to our ADI system resulted in improved image contrast. The use of ADIwith time-gating (gate width 250 ps) and linear polarization enabled visualization of sub-millimeter absorbing objectswith approximately eight times higher image contrast compared to ADI in a scattering medium equivalent to six timesreduced mean free path.