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Unformatted text preview: ECE 455: Optical Electronics Homework 3 Due: Sept. 20, 2011 1 Optical System Design A laser marking system using an Ar + laser operating at 488.0 nm is used to write serial numbers on electronic components. The focused laser beam burns the surface of the component making lines having widths essentially the same as the spot diameter, 2 w z . (This is actually the way it is done.) Design an optical system like that shown in Figure 1 by choosing d 2 , d 3 and the focal length f 1 of the lens so that the width of the lines in the letters is less than 0.03 cm. Assume that R 1 = 300 cm and d 1 = 60 cm. Note the solution is not unique. Figure 1: An optical system that could be used for laser etching 2 Modal Volume Consider the laser shown in Figure 2 which is to operate in the TEM 00 Gaussian mode at a wavelength of = 0 . 4 m. The modal volume of the laser is the volume of the laser medium ( n crystal = 2 . 4) that interacts with the laser beam. Assume that the modal volume of the laser is that portion of the laser medium which overlaps the cavity mode at radii r 2 w z , where w z is the spot size at z . Calculate (or approximate in a sensible way) the modal volume of this laser for d = 40 cm and R 1 = 80 cm, 400 cm, and 800 cm. Comment on how this trend in modal volume= 80 cm, 400 cm, and 800 cm....
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