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EE_424_Mid-Term_Exam_Sample

# EE_424_Mid-Term_Exam_Sample - lat/a Pm yew BB 414...

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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 thin-lens 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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EE_424_Mid-Term_Exam_Sample - lat/a Pm yew BB 414...

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