NAME: Mid-Term Exam 2 – PHYS 355 - OPTICS Mendes, Fall 2009, Oct 30 Start time: 10:00 a.m. End time: 10:50 am Open textbook, notes, homeworks, and quizzes Calculators allowed; no other electronic device allowed Where it is appropriate, make sure to provide physical units to your numerical answer (25 points) 1) Suppose we place a chamber of 10 cm long with flat parallel windows in one arm of a Michelson interferometer that is being illuminated by 600-nm light. If the refractive index of air is 1.00029 and all the air is pumped out of the cell, how many fringes will shift in the process? (25 points) 2) An opaque screen containing two small pinholes separated by 0.10 mm is illuminated by blue light from an argon ion laser 488 nm at normal angle of incidence. If the fringes on an observing screen are to be 10 mm apart (i.e., the distance between two dark fringes or two bright fringes is 10 mm), how far away should the screen be? (30 points) 3) A plane wave ( = 633 nm) falls normally on a long narrow slit of width 0.080 mm. a) Based on the Fraunhofer approximation, calculate the angles of diffraction corresponding to the first three minima (all at one side of the central peak). b) If an observation screen is placed (parallel to the aperture screen) at a distance of 1.8 m away from the aperture screen, determine the distance from the central peak to those first three minima. c) If a lens of focal length 100 mm is placed after the slit aperture and the observation screen is now placed at the back focal plane of the lens, determine the distance from the central peak to those first three minima. (20 points) 4) The need for higher storage capacity of information in optical disks has been increasing in recent years. The initial CD-ROM technology has used a semiconductor laser of 780-nm wavelength and a lens with a numerical aperture of 0.45. The newer DVD technology has typically used a 650-nm laser and lens with a numerical aperture of 0.65. Recently, the blu-ray technology has come to the market place with a semiconductor laser at 405 nm and using lens with 0.85 of numerical aperture. Considering that all those technologies use diffraction-limited lenses (i.e., lenses that are well-corrected for optical aberrations), determine the smallest linear dimension (i.e., diameter of the spot at the back focal plane of the lens) that can be read/write with each technology. Note: numerical aperture half diameter of lens / focal length .