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Unformatted text preview: lat/a. Pm yew BB 414 Mid—Term 1 Time: 1 Hour [2:30 PM — 3:30 PM] Name: Signature: Do Both Problems 1 and 2 I. A cw laser [wavelength A = 1000 nm] operating in the TEMOO Gaussian beam mode
is used for remote sensing and has to be expanded using the thinlens optics shown,
with L2 usually 20x L1. The laser minimum beam waist after the first lens L1 is (00 = 1 mm located at the focal plane FP. A second lens L2 placed at a distance of 30 cm
from the focal plane is used to recollimate the beam. [10%] (A)Using free space propagation formulae for Gaussian beam or the ABCD law for
laser beam, calculate the beam waist a) and the wavefront radius of curvature R of
the laser just before the lens L2. {5%} (B)What is the focal length of the lens L2 such that the exit beam just after the lens L2
has a plane wavefront [Rzinfinity}? [5%] (C) What is the far field expansion angle (divergence) of the laser after lens L2? 2. Consider a horizontal gay impinging on a curved surface defined by two media with refractive indices n;=1.5 and 112 = 1, respectively as shown. The Radius of curvature R of the
curve surface is R=I00 cm. The ray is 10 cm above the horizontal line [2 %] (a) Write down the ABCD matrix associated with the curved surface. [5%} (b) Caiculate the angle made by the exit beam with the horizontal. [3%] (c) At what distance behind the curved surface wilI parallel rays be brought to a focus? ...
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 Spring '11
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