The arrangement shown in Fig. P. 13.43 is used to convert a collimated laserbeam into a sp...

The arrangement shown in Fig. P. 13.43 is used to convert a collimated laserbeam into a spherical wave. The pinhole cleans up the beam; that is, it eliminates diffraction effects due to dust and the like on the lens. How does it manage it?

Figure P.13.43 (a) and (b) A high-power laserbeam before and after spatial filtering. (Photos courtesy Lawrence Livermore National Laboratory.)

(a)

(b)

(c)