Home Optics Experiments PE-0200 Polarisation of Light

Keywords:

  • Optical Activity
  • Double Refraction
  • Polarization of Light Sources
  • Linear Polarized Light
  • Elliptical, Circular Polarized Light
  • LED Light Source
  • Green Laser
  • Quartz Retarder Plate
  • Mica Retarder Plate
  • Photodetector
  • Light Power Control
  • Malus’ Law

 

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-0200 Polarisation of Light

Educational Kit PE-0200 Polarisation of Light

In the year 1809, Etienne Malus discovered the polarization of light by reflection and stated a law which describes the intensity distribution of polarized light as a function of the relative orientation of a polarization analyser. At that time his findings were in contradiction to the presumption of light waves being longitudinal rather than transversal. His discovery had far reaching consequences for the wave theory of light, and his unambiguous experimental results launched a big debate, among the leading scientists about the wave properties of light. Finally, as a compromise light was conceded to have transversal as well as longitudinal character. Two years later Dominique Arago investigated a sample of quartz and discovered its optical activity, a property of many natural and also synthetic materials. Later on, Augustine Fresnel could explain the effect of optical active materials on light by introducing the phenomenon of circular birefringence. In this series of experiments the polarization state of the light sources in use is determined. Furthermore, polarized light is used to prove the Malus’ and Fresnel’s Laws with respect to their states on polarization. The influence of crystal wave plates and optically active materials on polarization is studied.

PE-0200 Polarisation of Light

PE-0200 Polarisation of Light how it works

As light source either as coherent “green” laser or a blue or white light emitting LED is used. In case of using a LED an achromat is used to form an almost parallel beam. By means of a polarisation analyser and the photodetector the intensity of the light source as function of the analyser angle is measured. As a result, three plots are created representing the polarisation of the green laser and the blue and white LED.

PE-0200 Polarisation of Light how it works

By using an additional polarizer the emitted light is polarised. If the analyser angle is set to 90 degrees with respect to the polarizer the passed intensity is a minimum and for 0 degree a maximum. Between these values the transmitted intensity behind the analyser is according to the Malus’ law. This setup allows the verification of Malus’s law and demonstrates furthermore an arrangement to change the intensity of a light source without changing the operating current.

PE-0200 Polarisation of Light how it works

Material which change the polarisation of transmitted light are termed as optical active. Such natural materials are for instance crystalline quartz, calcite or mica. Within the frame of the experiment three crystalline plates made of quartz and mica are used. The plates are mounted in a click mount with an index mark. The plate is placed behind the polarizer and the transmitted intensity is measured as function of the analyser angle. The resulting angular intensity plot informs about the particular optical activity.

 

PE-0200 Polarisation of Light

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Educational Kit PE-0200 Polarisation of Light