Associated Airy disk as detected by the CCD camera. The yellow bar in (b) represents 2 times the spot size $w_\text{B}$ of the Bessel beam’s central core. $w$ in (d) is the spot size of the Airy disk.[]{data-label="fig:bessels"}](MaziluFig10.pdf){width="75.00000%"}

![Experimental OEi spot size minimization. *Top row*: $I_{\textrm{Num-S}}(z_{2})$ for different ROI radii in pixel as indicated in the top left corner of all graphs shown. The ROI is exemplary indicated as a dashed ring in the left hand side intensity distribution. The number in the bottom left corner represents the spot size $w$ in units of the reference spot size $w_{\textrm{B}}$. *Central row*: Optimized experimental distribution as RGB encoded onto the SLM. *Bottom row*: Intensity distributions $I_{\textrm{Exp-S}}(z_{2})$. The relative spot size $w/w_\text{B}$ is indicated in the lower left corner.[]{data-label="fig:spots"}](MaziluFig11.pdf){width="75.00000%"}

The results of the performed OEi spot size minimization are shown in Fig. \[fig:spots\] for different sizes of the ROI. To begin with, the comparison of the Num-S intensity distribution $I_{\textrm{Num-S}}(z_{2})$ (top row) and the Exp-S intensity distributions $I_{\textrm{Exp-S}}(z_{2})$ (bottom row) clearly reveals good agreement and thus verifies the linearity of our optical system as elucidated above. For completeness, the central row shows the Exp-S superposition in RGB format as encoded onto the 