A collimated laser beam emerging from a commercial HeNe laser has a diameter of about 1 millimeter. In order to convert this beam into a well-collimated beam of diameter 10 millimeter, two convex lenses are to be used. The first lens if of focal length 1.5 centimeters and is to be mounted at the output of the laser. What is the focal length, f of the second lens and how far from the first lens should it be placed?
B. f = 10 cm, Distance = 10 cm
C. f = 10 cm, Distance = 11.5 cm
D. f = 15 cm, Distance = 15 cm
E. f = 15 cm, Distance = 16.5 cm
(GR9677 #58)
Since two convex lenses are used, we can treat this system as a telescope.
Magnification, M = fobject / feye = 10
fobject = 10 feye = 10 × 1.5 cm = 15 cm
D = fobject + feye = 10 + 1.5 = 16.5 cm
Answer: E
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