Introduction
The aim of this experiment is to investigate diffraction phenomena. It is possible to explore diffraction patterns for different objects and to investigate the influence of the object position relative to the position of the light source and the detector on the measured pattern. In a simulation model the dependence of the diffraction pattern on the nature and size of the different objects and on experimental parameters can be investigated and compared with the measured data.
Theoretical Background
If an object obstructs a coherent spherical wave front (light from a point source) then according to the principle of Huygens every light point in that plane of the object will generate secondary wave fronts. This will create a diffraction pattern at a certain distance from the object. The concepts as interference, diffraction and cornu-spiral are visualized and interactively presented in this experiment by means of applets.
Experimentation Method
A diffraction pattern can be measured if an object is placed in the wave front of the light source and the light detector scans in a plane perpendicular to the secondary wave fronts. The light intensities measured at different detector positions will result in a measured diffraction pattern. This diffraction pattern can be compared with the data of a simulation model.
Motivation to perform this experiment remotely
In this experiment good alignment is a time consuming element. If alignment is not a learning objective it is better to start with a working setup. It gives the student more time to investigate the different diffraction phenomena.
Setup
Short description
The point source which is needed in this experiment is created by means of a He-Ne laser and a spatial filter. For studying the diffraction phenomena it is possible to choose out of eight different objects placed in a carrousel and/or change the distance between the chosen object and the light source. A diffraction pattern can be measured by scanning the detector through the diffraction pattern. Light intensities will be recorded by the data acquisition board in the computer.
Schematic view
Remote Interface
Variables that can be controlled remotely
- Distance object - point source
- The carrousel to choose one of the eight objects. (wires, single-slit, double-slit, etc)
- Scanning parameters (start-, stop-position of the detector and the distance between two adjacent measurement points).
Variables that can be measured remotely
- The light intensity and the position of the detector.
- The distance object - point source by means of a ruler
What is visualized remotely?
- Schematic view of the experiment
- Diffraction objects
- Diffraction pattern with scanning parameters
- The model calculation
- Webcam images:
- laser with spatial filter and the object carousel;
- a ruler with read out for object position
- the detector and a screen showing the diffraction pattern
Educational
Learning Objectives
- Gain knowledge of Fresnel diffraction
- WDetermine scanning parameters
- Fit measured data to a model by changing various parameters
Target Group
- Bachelor students in physics.
Professional Relevance
- Using a physical phenomenon to measure object properties accurately.