Principle

Pin hole diaphragms and circular obstacles are illuminated with laser light. The resulting intensity distributions due to diffraction are measured by means of a photo diode.

Tasks

1. The complete intensity distribution of the diffraction pattern of a pin hole diaphragm (D1 = 0.25 mm) is determined by means of a sliding photo diode. The diffraction peak intensities are compared with the theoretical values. The diameter of the pin hole diaphragm is determined from the diffraction angles of peaks and minima.
2. The positions and intensities of minima and peaks of a second pin hole diaphragm (D2 = 0.5 mm) are determined. The diffraction peak intensities are compared with the theoretical values. The diameter of the pin hole diaphragm is determined.
3. The positions of minima and peaks of the diffraction patterns of two complementary circular obstacles (D*1 = 0.25 mm and D*2 = 0.5 mm) are determined. Results are discussed in terms of Babinet's Theorem.

Learning objectives

• Huyghens principle
• Interference
• Fraunhofer and Fresnel-diffraction
• Fresnel's zone construction
• Coherence
• Laser
• Airy disk
• Airy ring
• Poissonâ's spot
• Babinet's theorem
• Bessel functions
• Resolution of optical instruments