A laser beam of diameter d-1.2 mm is directed along the optical axis of a thin l

Question

A laser beam of diameter d-1.2 mm is directed along the optical axis of a thin lens of focal length +6.8 cm (see figure below). How far from the lens will the beam be focused? (b) A second postive lens is placed to the right of the first. Light emerges from the second lens in a parallel beam of diameter d2 3.0 mm. Thus the combination of lenses acts as a beam expander. Find the focal length of the second lens the distance bebveen the lenses. Find the image distance and linear magnification for a small object on the optical axis, 18.2 cm from a lens of focal length -9.6 cm. mage distance

Explanation / Answer

a) 1/s + 1/s' = 1 / f

s = infinity

1/s' = 1 / f

s' = f = 6.8 cm

b) [d1/2] / f1 = [d2/2] / f2

f2 = [ [d2/2] / [d1/2] ] * f1

f2 = [d2 / d1] * f1 = [3 / 1.2] * 6.8

focal length of second lens = 17 cm

c) distance between lenses = f1 + f2

= 6.8 + 17

distance = 23.8 cm

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