Abstract
Phase front modulation was previously used to refocus light after transmission through scattering media. This process has been adapted here to work in reflection. A liquid crystal spatial light modulator is used to conjugate the phase scattering properties of diffuse reflectors to produce a converging phase front just after reflection. The resultant focused spot had intensity enhancement values between 13 and 122 depending on the type of reflector. The intensity enhancement of more specular materials was greater in the specular region, while diffuse reflector materials achieved a greater enhancement in non-specular regions, facilitating non-mechanical steering of the focused spot. Scalar wave optics modeling corroborates the experimental results.
Highlights
All materials scatter light, either in a transmissive manner or reflectively, to some degree.The ground work for imaging with scattered light was put forth by Freund in which the random scatter was treated as a complex field that interfered with incident light to produce speckle patterns
We demonstrate reflective inverse diffusion using feedback-based wavefront shaping methods adapted from the original transmissive inverse diffusion research
With a mirror positioned at the focus of the positive lens, the creation of a focused spot on the charge-coupled device (CCD) requires shifting the focus of the positive lens the distance from the mirror to the CCD
Summary
Either in a transmissive manner or reflectively, to some degree.The ground work for imaging with scattered light was put forth by Freund in which the random scatter was treated as a complex field that interfered with incident light to produce speckle patterns. Just as Freund predicted a decade earlier, properly-modified incident light allowed the scattering medium to behave as a lens [1]. This process, called “inverse diffusion” by the authors, is capable of simulating a phase grating that allows control of the focus spot location in the observation plane by adjusting the wavefront shape. N =1 where tmn is the mn-th complex-valued element of the transmission/reflection matrix relating the light from the n-th spatial light modulator (SLM) segment to the m-th segment in the observation plane, and. The source field is segmented by the SLM into NT segments and reflected off the scattering medium.
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