Optical imaging of objects in turbid medium with ultrashort pulses

Photons are seriously scattered when entering turbid medium; thus the images of objects hidden in turbid medium can not be obtained by just collecting the transmitted photons. Early-arriving photons, which are also called ballistic or snake photons, are much less scattered when passing through turbid medium, and contains more image information than the late-arriving ones. Therefore, objects embedded in turbid medium can be imaged by gathering the ballistic and snake photons. In the present research, we try to recover images of objects in turbid medium by simultaneously `time-gate' and `polarization-gate' to obtain the snake photons. An Argon-pumped Ti-Sapphire laser with 100 fs pulses was employed as light source. A streak camera with 2 ps temporal resolution was used to extract the ballistic and snake photons. Two pieces of lean swine meat, measured 4 mm×3 mm and 5 mm×4 mm, respectively, were placed in a 10 cm×10 cm×3 cm acrylic tank, which was full of diluted milk. A pair of a polarizer and an analyzer was used to extract the light that keeps polarization unchanged. The combination of time gating and polarization gating resulted in good images of objects hidden in turbid medium.