L1-C

MEASURING BEAM DIVERGENCE
The divergence of a CW laser beam can be determined by measurement of the beam diameter at two points (Figure 8).

Controlling the beam after it is emitted out of the optical cavity
Some applications require a laser beam with low divergence. To reduce ? we must expand the waist of the beam. This can be achieved by expanding a laser beam with a beam expander.

Beam Expander
The most common type of beam expander is derived from the Galilean telescope which usually has one negative input lens and one positive output lens, as shown in Figure 9. The input lens presents a virtual beam focus at the output. For low expansion ratios (1.3-20?), the Galilean telescope is most often employed due to its simplicity, small package size, and low cost.Another Beam expander is based on the telescope developed by Kepler The first positive lens has short focal length and small diameter, while the second positive lens has long focal length and large diameter. The distance between the lenses is exactly equal to the sum of the focal lenses