Fig. 1. MC algorithm flowchart.

Fig. 2. (a) Photon initialization for Gaussian beams. (b) Generation of Bessel beams using the axial cone lens.

Fig. 3. For (a) λ = 450 nm and (b) λ = 520 nm, the output voltages of the MPPC based on the Gaussian beams versus the Bessel beams at different distances.

Fig. 4. Output voltages based on (a) Gaussian and (b) Bessel beams for three water quality cases and two wavelength cases (λ = 450, 520 nm).

Fig. 5. Power gains obtained at different half angles of the FOV after using the lens (n = 1.46) for (a) D = 1 m, λ = 450 nm, (b) D = 11 m, λ = 450 nm, (c) D = 1 m, λ = 520 nm, and (d) D = 11 m, λ = 520 nm.

Fig. 6. Experimental scenario diagram.

Fig. 7. Output voltages based on 450 and 520 nm lasers for three water quality conditions in a closed environment.

Fig. 8. Output voltages based on 450 nm Bessel beams for three water quality conditions.