Measuring the Reflection Matrix of a Rough Surface

Abstract

Phase modulation methods for imaging around corners with reflectively scattered light required illumination of the occluded scene with a light source either in the scene or with direct line of sight to the scene. The RM (reflection matrix) allows control and refocusing of light after reflection, which could provide a means of illuminating an occluded scene without access or line of sight. Two optical arrangements, one focal-plane, the other an imaging system, were used to measure the RM of five different rough-surface reflectors. Intensity enhancement values of up to 24 were achieved. Surface roughness, correlation length, and slope were examined for their effect on enhancement. Diffraction-based simulations were used to corroborate experimental results.

Light transmission and internal scattering in pulsed laser-etched partially-transparent silicon wafers

“…Surface texture on front, rear, and sidewalls contributes to enhance internal three-dimensional texturing. Surface reflection is also reduced by surface texturing based on diffractive and physical optics [7]. Reduction in reflection losses leads to higher transmission.…”

Beam Formation and Vernier Steering Off of a Rough Surface

“…The laboratory setup in the experiment was called a focal plane setup, shown in Figure 1 . Previous works discuss the merits of different optical setups for achieving reflective inverse diffusion [ 12 , 13 , 20 ]. The optical source is a frequency-stabilized CW laser at 632.8 nm, expanded and collimated to fill the SLM at near-normal incidence.…”

“…Properly modulated incident light has been shown to refocus after interfering with scattering surface or turbid media in a process dubbed inverse diffusion. Numerous feedback-based algorithms and approaches such as matrix measurements have been developed that determine the required modulation to refocus light after transmissive and reflective scattering [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. In particular, Vellekoop provides a detailed summary of several different approaches taken [ 11 ].…”

“…Existing wavefront shaping techniques have been applied to microscopy, tomography, fiber optics, super-resolution imaging, and a growing number of other use cases [ 11 , 15 , 16 , 17 , 18 , 19 ]. Applications of wavefront shaping specifically involving reflection from a rough surface as opposed to transmission through turbid media are not as numerous in the literature, but there is a continuing interest to utilize reflective inverse diffusion to image around corners [ 9 , 12 , 13 , 14 , 20 , 21 ]. There also could exist unexplored use cases for wavefront shaping in LiDAR with certain limitations.…”

“…These active methods depend on some intermediate surface that has a direct line of sight to the scene and can reflect illumination into it. The intermediate surface functions as either a virtual illumination source, a virtual detector, or both [ 12 , 13 , 14 , 24 , 25 ]. An indirect imaging system with these imposed limitations must be able to rapidly create and then control a virtual illumination source at any surface, even in the presence of noise.…”