PE-0400 Diffraction of Light

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

PE-0400 Diffraction of Light
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.

Principle set-up of PE-0400 Diffraction of LightPrinciple set-up of PE-0400 Diffraction of Light

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.

Description of the components of PE-0400 Diffraction of LightDescription of the components of PE-0400 Diffraction of Light

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, consisting of:
Item Code Qty. Description
1 DC-0020 1 LED and Photodiode Controller
2 DC-0800 1 CCD Camera Controller
3 DC-0820 1 CCD Camera Module
4 LQ-0020 1 Green (532 nm) DPSSL in ø25 housing
5 LQ-0210 1 Red LED in ø 25 housing
6 MM-0020 3 Mounting plate C25 on carrier MG20
7 MM-0060 1 Filter plate holder on MG20
8 MM-0110 1 Translucent screen on carrier MG20
9 MM-0420 1 Four axes kinematic mount on carrier MG20
10 MP-0150 1 Optical Bench MG-65, 500 mm
11 OC-0040 2 Plano-convex lens f=40 mm in C25 mount
12 OC-0280 1 Cylindrical lens f=80 mm in C25 mount
13 OC-0360 1 Beam Expander x6 in ø25 housing
14 OC-0470 1 Wire 0.05 mm in 50x50 frame
15 OC-0480 1 Circular apertures in 50x50 mm frame
16 OC-0482 1 Gauze 300 mesh in 50x50 mm frame
17 OC-0484 1 Single slit 0.06 mm in 50x50 mm frame
18 OC-0486 1 Double slit in 50x50 mm frame
19 UM-PE04 1 Manual Diffraction of Light


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