Contents I. Introduction
Optical imaging of hidden objects in highly scattering media is important in many areas such as in clouds [1], fogs [2], or aerated sprays [3]. When light pulses propagate through a turbid medium, the transmitted pulses consist of a ballistic component, a snake component, and a diffuse component [4]. The ballistic photons that carry the object information migrate through a turbid medium undeviated in the forward direction and arrive first. The snake component consists of the photons that have undergone only a few scatterings along quasi-straight-line paths. The diffuse component that has been scattered randomly in all directions loses the image information and constitutes the noise [5]. The image quality is often degraded by multiple scattering in a scattering medium, which presents the main challenge associated with optical imaging [6]. Many different techniques have been introduced to image or probe objects embedded in scattering media [7]–[10]. A feasible way to suppress multiple scattered photons and improve the visualization of objects hidden in the turbid medium is by employing a short time gate based on nonlinear optical phenomena, such as degenerate four wave mixing [11], second-harmonic generation [12], or an optical Kerr gate (OKG) [13], [14]. Among the available time gating techniques, OKG imaging has been investigated widely due to its advantages, such as no need for satisfying the phase matching condition or the high intensity of the imaging signal [15]. However, most studies on OKG imaging focus on the macroscopic imaging of hidden objects in a scattering medium.
