Build a Beam Expander (a Kepler telescope) using two converging lenses, according to the figure below:

If the distance between the lenses is equal to the sum of their focal lengths (f₁+ f₂), then the width of the emergent beam (W₂) related to that of the incoming (W₁) beam by :

• Measure the divergence of the beam after you expand it. Repeat the same experiment.
• Explain the difference, if any, between the divergences of the laser beam with and without the laser expander.