Multiple Slit Diffraction

This demonstration uses a Class IIIb laser capable of causing immediate eye injury. Never aim the laser toward any area where students may be present. The reflection shield must remain in position whenever the laser is energized to prevent backscatter from entering students' eyes. Use appropriate laser safety eyewear during alignment and whenever the laser is operating. Ensure the beam terminates on a non-reflective surface.

Do not remove or reposition the reflection shield while the laser is turned on. Complete all alignment procedures before students enter the room, or ensure students are positioned safely behind the laser. Post appropriate laser warning signs if required by institutional policy. Have emergency shutdown procedures clearly established.

Purpose

A Cornell plate provides multiple-slit patterns and gratings of various densities. Students observe how increasing the number of slits sharpens the principal maxima while keeping their angular positions fixed, and how grating line density controls the angular separation of orders.

$Green laser on adjustable stand with Cornell diffraction plate, producing a multiple-slit interference pattern on white paper attached to the blackboard; pattern shows a bright central spot with a few side maxima$

$Same setup with a different slit or grating on the Cornell plate, showing sharper and more numerous discrete diffraction spots in a horizontal line on the screen$

Figure 1: Setup with Cornell plate showing a multiple-slit pattern: bright central maximum with several side maxima visible on sketch paper magnetically attached to the blackboard.

Figure 2: Switching to a higher-N slit pattern or grating on the Cornell plate produces sharper, more numerous principal maxima -- demonstrating how increasing the number of slits narrows the peaks.

Optical Slider

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Polished Steel Plate

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Danger: Class IIIb Laser Hazard

Warning: Laser Safety Protocols

Purpose

Safety Warnings

Danger: Class IIIb Laser Hazard

Warning: Laser Safety Protocols

Purpose