The laser beam then passes through a series of lenses as shown in Figure 4. Lenses L1 and L2 are positioned with overlapping focal lengths so that the output of L2 is a highly parallel, expanded beam. This was to remove large spherical aberrations due to imperfections in the quartz lenses. | The laser beam then passes through a series of lenses as shown in Figure 4. Lenses L1 and L2 are positioned with overlapping focal lengths so that the output of L2 is a highly parallel, expanded beam. This was to remove large spherical aberrations due to imperfections in the quartz lenses. |