Question

Problem 6.1: Gaussian beam through a thin lens (5P) A collimated NeHe laser with wavelength ? = 633nm and beam diameter ? = 2mm is focused by a thin lens with focal length ? = 6mm. 10cm behind the thin lens is a spherical screen placed. The screen has the same curvature as the wave front at this position. The propagation direction of the beam is in z-direction and it’s ? = 0 at the lens’ position. (a) Draw a sketch of the situation and draw in the parameters mentioned above. (1P) (b) Calculate the minimal diameter of the beam (how is it called?) between lens and screen. Which radius has the wavefront here? (1P) (c) Which radius of curvature has the screen? (0.5P) (d) Which beam radius has the beam at the screen? (0.5P) (e) Now we are looking at the intensity distribution of the beam on the z-axis (? = 0). Which peak intensity can you measure on the screen? Give the value depending on the incident intensity ?0. At which distance from the lens is the Intensity ?0/?? (1P) (f) In the next case we consider the beam intensity distribution perpendicular to the z-axis at ? = ?. Where is the intensity dropped to ?0/?? (1P)

Answer 1