Home Optics Experiments PE-0400 Diffraction of Light

Keywords:

  • Huygens Principle
  • Single and Multiple Slits
  • Diffraction of LED Light
  • Diffraction at a Wire
  • Babinet Theorem
  • Diffraction of Coherent Light

 

Basic experiment

Intended institutions and users:

Physics Laboratory

Engineering department

Electronic department

Biophotonics department

Physics education in Medicine

 

Introduction

How it works ...

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PE-0400 Diffraction of Light

Educational Kit PE-0400 Diffraction of Light

All objects which restrict the free propagation of light cause diffraction. Although this phenomenon is always present, it is usually neglected, because the effect is too insignificant for the topic of investigation. But if light hits sharp edges, diffraction will appear clearly and cannot be neglected, especially when light is diffracted on very narrow openings like holes or slits. Christian Huygens formulated his observation of diffraction in the 17th century applying the principle of elementary waves. In 1800 Fresnel and Fraunhofer both studied the effect of diffraction in detail. Fresnel used divergent light for his investigations, whereas Fraunhofer used parallel light created by a pair of lenses. Both techniques are termed  as Fresnel and Fraunhofer diffraction respectively.

This experiment offers both types of diffraction. Experiments are performed using monochromatic laser light which will be diffracted at slits and holes of various widths. Thin wires impressively proves the Babinet theorem which states  that complementary masks (slit, wire) result in the same diffraction pattern. The obtained diffraction patterns are imaged on a white screen and the pattern can also be recorded by a CCD camera.

 

PE-0400 Diffraction of Light

PE-0400 Diffraction of Light how it works

The figure on the left shows the arrangement using a laser. In case a LED is used, the Beam expander is exchanged against a collimating lens. To obtain crisp diffraction fringes most of the light should hit the diffraction pattern. In case of using a slit an extra cylindrical lens is used to convert the round beam into a line structure. When demonstrating the diffraction at a hole the round laser beam is used as it is.

PE-0400 Diffraction of Light Descriprion of the components I

Within the experiment a red emitting LED (5) or a green emitting laser (4) are used. For both light sources the controller (1) provides the individual current and voltage. The controllers microprocessor reads the property of the connected light source and sets the parameter accordingly. When using the green laser and a vertical slit (17,18) or wire (14), the beam expander (13) is needed to create in conjunction with the cylindrical lens (12) a vertical line shape. Different types of diffraction elements can be inserted to the plate holder (7). To verify the Babinet’s theorem a slit (17) and a wire (14)with same dimensions is used. Furthermore the diffraction fringes a double slit (18), a circular aperture (15) and a two dimensional structure (16) are created and recorded. For a first view, the translucent screen (8) is used. The fringes on the screen are recorded by the high resolution (8 MP) CCD camera (3) and are displayed live on the digital video controller (2). The image can be taken as still photo or as video. The video controller provides USB inputs for a memory stick or other external devices like mouse or keyboard. The HDMI output allows the connection to a projector in the lecture hall to demonstrate a live experiment.

 

PE-0400 Diffraction of Light

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