Abstract
This paper investigates the reference-defining-criterion problem in the field of light focusing through scattering media. In many analogous light focusing experiments, the enhancement values differ greatly from each other. By analyzing the focusing picture after optimizations, we concluded that the discrepancy in enhancement originates from the unclear definition of reference boundary. By averaging multiple speckle backgrounds, we found that the intensity of speckle background obeys circular Gaussian distribution. Based on the intensity statistics and Gaussian-function fitting to the speckle background, we proposed a clear reference-defining criterion– 1/e2 criterion. With this reference-defining criterion, we have carried out light focusing experiments with the speckle backgrounds possessing different shape and size. The enhancements obtained from the repetitive experiments for both weakly scattering medium and strongly scattering medium were all in the reasonable range, demonstrating its validity and universality. This criterion will provide a comparison standard for light focusing experiments in wavefront-shaping field.
Highlights
Spatial inhomogeneities in the refractive index of random photonic materials such as paper, paint, and biological tissue cause multiply scattering of light
In the iterative optimization method, the optimization algorithm controls the modulator to modulate the phase or amplitude of the incident light based on a feedback signal to perform iterative optimizations until finding the optimal mask for creating a focus[5]
The enhancements obtained from the testing experiments for both weakly scattering medium and strongly scattering medium were all in the reasonable range
Summary
Spatial inhomogeneities in the refractive index of random photonic materials such as paper, paint, and biological tissue cause multiply scattering of light. The light focusing experiments performed in this paper are based on the amplitude-only genetic algorithm with the DMD. In many analogous amplitude-optimization experiments with the TPI discriminant or the SBR discriminant, the practical enhancements were rarely able to achieve the theoretical maximum or value of simulation.
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