Single-Slit Diffraction: Transitioning from Geometric Optics to the Fraunhofer Regime

Abstract

Suppose a red laser beam (of wavelength λ equal to 0.660 μm) is expanded using an optical telescope into a collimated, approximately plane wave that is 5.68 mm in diameter. Pass that beam through a tall rectangular slit whose width a is gradually reduced from 3.30 to 0.100 mm. Look at its image on a screen located at a distance L from the slit equal to 0.656 m. As the slit is narrowed, you predict that the width of the pattern will: smoothly increase,smoothly decrease,increase and then decrease, ordecrease and then increase.