Polarisation through lambda-quarter wave plates

Principle

Monochromatic light falls on a mica plate perpendicular to its optic axis. At the appropriate plate thickness (lambda/4, or quarter-wave plate) there is a 90° phase shift between the ordinary and the extraordinary ray when the light emerges from the crystal. The polarisation of the emergent light is investigated at different angles between the optic axis of the lambda/4 plate and the direction of polarisation of the incident light.

Benefits

• The principles Polaroid glasses work on
• Discover ways to modify certain attributes of light
• Make the electric vector go round and round

Tasks

1. To measure the intensity of plane polarised light as a function of the position of the analyser.
2. To measure the light intensity behind the analyser as a function of the angle between the optic axis of the lambda/4 plate and that of the analyser.
3. To perform experiment 2. with two lambda/4 plates one behind the other.

Learning objectives

• Plane
• Circularly and elliptically polarised light
• Polariser
• Analyzer
• Plane of polarisation
• Double refraction
• Optic axis
• Ordinary and extraordinary ray