Fig. 1. Schematic of the effect of mask with multiple apertures on the laser speckle

Fig. 2. Experimental setup

Fig. 3. Speckle images for different d between the two apertures with the diameter of 2 mm. (a) d =3 mm; (b) d =4 mm; (c) d =5 mm; (d) d =6 mm; (e) d =7 mm; (f) d =8 mm

Fig. 4. Speckle contrast corresponding to different d between the two apertures with the diameter of 2 mm

Fig. 5. Speckle contrast corresponding to different d between the two apertures with the diameter of 4 mm

Fig. 6. Granules observed in the speckle image for the apertures with different diameters in the defocus case. (a) d =2 mm, d =5 mm; (b) d =4 mm, d =7 mm