A double convex lens is used to couple a laser beam of diameter 5mm into an optical fiber with a numerical aperture of 0.5. The minimum focal length of the lens that should be used In order to focus the entire beam into the fiber is:

A double convex lens is used to couple a laser beam of diameter 5mm in

1.	A double convex lens is used to couple a laser beam of diameter 5mm into an optical fiber with a numerical aperture of 0.5. The minimum focal length of the lens that should be used In order to focus the entire beam into the fiber is:
A.	1.44mm
B.	2.50mm
C.	4.33mm
D.	5.OOmm
Answer» C. 4.33mm