beam shown in Fig. \[fig7\](b), where the ROI is indicated as dashed circle. For comparison, the red dot indicates the location of the reference beam in the $\Delta r/w_{\textrm{B}}$ vs. $R/R_{\textrm{B}}$ plot. (b) Strehl ratio vs relative ROI radius $R/R_{\textrm{B}}$.[]{data-label="fig8"}](MaziluFig8.pdf){width="12cm"}

Experimental OEi {#s:sec4}
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Experimental implementation of the OEi concept
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To perform an experimental OEi optimization we have used the following setup: A $\textrm{HeNe}$ laser beam is expanded and subsequently amplitude modulated by a spatial light modulator (SLM) display operating in conjunction with a pair of crossed polarizers. Analogously to a liquid crystal display on a computer or laptop monitor, the liquid crystal SLM display rotates the polarization of the incident light by an angle depending upon the voltage applied to the display pixels. The amplitude modulated beam is then imaged onto a second SLM display through a pair of lenses. This second SLM display along with a subsequent Fourier lens and aperture served to modulate the phase of the laser beam in the standard first order configuration [@DiLeonardo2007]. The field modulations of interest were encoded as RGB images where the blue channel represented the amplitude and the green channel the phase modulation. The SLM controller extracted these information 