Fig. 2

Simulated intensity distributions generated by the MDOE for z = a 15 cm, b 20 cm, c 25 cm, d 30 cm, e 35 cm, f 40 cm and g 45 cm. Simulated intensity distributions generated by the DL for z = h 15 cm, i 20 cm, j 25 cm, k 30 cm, l 35 cm, m 40 cm and n 45 cm. The white broken line is attached to (a–g) to indicate the rotation angle of the spiral beam. The cross-section of the autocorrelation of the intensity distributions (a–n) are compared in (o–u), where blue is for DL and red is for MDOE