Coherence and width of spectral lines with the Michelson interferometer

Principle

The wavelengths and the corresponding lengths of coherence of the green spectral lines of an extreme high pressure Hg vapour lamp are determined by means of a Michelson interferometer. Different double slit combinations are illuminated to verify the coherence conditions of non punctual light sources. An illuminated auxiliary adjustable slit acts as a non punctual light source.

Benefits

• Study the quantity that allows light to be used in interference experiments
• Analyze different spectral lines of a mercury lamp
• Make practical use of a Michelson interferometer to characterize light

Tasks

1. Determination of the wavelength of the green Hg spectral line as well as of its coherence length.
2. The values determined in 1. are used to calculate the coherence time and the half width value of the spectral line.
3. Verification of the coherence condition for non punctual light sources.

Learning objectives

• Fraunhofer and Fresnel diffraction
• Interference
• Spatial and time coherence
• Coherence conditions
• Coherence length for non punctual light sources
• Coherence time
• Spectral lines (shape and half width value)
• Broadening of lines due to Doppler effect and pressure broadening
• Michelson interferometer
• Magnification