# Beam Formation and Vernier Steering Off of a Rough Surface
## 4 Conclusions  
The GA is able to optimize the SLM phase mask with relative speed in laboratory conditions that offer stability. However, it is unclear what level of optical power or enhancement of the refocused beam that is needed to meet the requirements for indirect imaging. Further analysis including link budget analyses of possible scenes is needed to determine the level of enhancement that is required of the wavefront shaping algorithm. Independent of algorithm improvements, advances in SLM technology to support faster update speeds will proportionally speed up the wavefront shaping process, and the availability of low RIN lasers can also improve algorithm performance. The SLM circular-shift method of beam steering is able to create small changes in the pointing direction of refocused beams. For this experimental geometry, circular shifts could be made to modify the pointing direction in increments as little as several thousandths of a degree. However, this method suffers large decreases in efficiency when applied to white paint, which is a bulk scatterer. The nickel sample fared better, likely because it is a surface scatterer. Depending on what level of losses are acceptable, the circular shift method could be used as a vernier beam steering adjustment to correct the overall scan angle to a precision below a tenth of a degree for reflective surfaces down to several thousandths of a \begin{table}
\begin{tabular}{c c c} \hline \hline
**Scan: Material, Axis** & **Equation (4) \(\theta_{scan}\) Increment** & **Measured \(\theta_{scan}\) Increment** \\ \hline Nickel, horizontal & 0.0343\({}^{\circ}\)\(\pm\) 0.0009\({}^{\circ}\) & 0.0363\({}^{\circ}\)\(\pm\) 0.0004\({}^{\circ}\) \\ \hline Nickel, vertical & 0.0344\({}^{\circ}\)\(\pm\) 0.0009\({}^{\circ}\) & 0.0340\({}^{\circ}\)\(\pm\) 0.0006\({}^{\circ}\) \\ \hline Paint, horizontal & 0.0343\({}^{\circ}\)\(\pm\) 0.0009\({}^{\circ}\) & 0.0328\({}^{\circ}\)\(\pm\) 0.0004\({}^{\circ}\) \\ \hline Paint, vertical & 0.0344\({}^{\circ}\)\(\pm\) 0.0009\({}^{\circ}\) & 0.0363\({}^{\circ}\)\(\pm\) 0.0004\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Predicted and observed scan angle increments due to a 16-pixel SLM shift. These values are the angular increments of \(\theta_{scan}\) between each grid square in Figures 4 and 5. Because the SLM was shifted 16 pixels at a time, the actual minimum scan angle increment is \(\frac{1}{16}\) these reported values. degree. A method for coarse adjustments of the scan angle to accommodate a wider field of view is still required. It was demonstrated that a genetic algorithm may be the best choice of all iterative algorithms for maximizing the enhancement of refocused beams in reflective inverse diffusion. It was also demonstrated that circular shifts of the SLM phase mask in a focal plane system can be used for high precision vernier adjustments of a refocused beam's pointing direction for a surface scattering sample. The circular shift method suffered large losses with the bulk scattering sample and may only be suitable for surfaces with high surface reflection. Finally, a method for wide field of view beam steering of the light in reflective inverse diffusion must still be discovered. Conceptualization, E.K.N., K.W.B., and S.D.B. ; methodology, E.K.N. ; software, E.K.N. ; validation, E.K.N., K.W.B., and S.D.B. ; formal analysis, E.K.N., K.W.B., and S.D.B. ; investigation, E.K.N. ; resources, K.W.B. ; data curation, E.K.N. ; writing--original draft preparation, E.K.N. ; writing--review and editing, K.W.B. and S.D.B. ; visualization, E.K.N. ; supervision, K.W.B. ; project administration, K.W.B. ; funding acquisition, K.W.B. All authors have read and agreed to the published version of the manuscript. This research received funding from the Air Force Office of Scientific Research. Data Availability Statement: Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.