Polycopiated : Practical Work of wave optics : For students of 3rd LMD Fundamental physics speciality
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Date
2025
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Faculty of Science
Abstract
When two or more light waves are superimposed, it is generally not possible to describe the
observed phenomena in a simple way. Consider the case of two waves from a single point and
monochromatic source: in the superposition region, the luminous intensity varies from one
point to another between maxima which exceed the sum of the intensities of two waves taken
separately and minima which may be zero. This is the phenomenon of interference.
To specify the conditions that two waves must meet in order to interfere, it is not necessary to
have a precise idea of the nature of electromagnetic waves. It is sufficient to accept the
following principles:
1- Monochromatic light is composed of vibrations of a single frequency.
2- The electromagnetic vibrations propagate at the speed of light v = c n, with c: speed of
light and n: refractive index.
3- They are transverse to the direction of propagation.
4- They can be represented by a sinusoidal function.
5- The duration of light emission by an atomic emitter is in the range of 10-9 to 10-8 seconds,
that is to s ay that the waves emitted have a length between 30 cm and 3 cm. In other words,
each atomic oscillator emits a very fine monochromatic wave for a short time, then another
without phase relation to the previous one: the source is temporarily incoherent.
6- Each atomic oscillator works independently of its neighbors. There is generally no
permanent phase relationship between the radiations they emit. It is said that the source is
spatially inconsistent.
7- The wavelengths of the neighbouring oscillations are generally independent, in this case all
radiations are present in the continuous spectrum and the light is called white.
8- The radiation polarizations emitted by the various oscillators are independent and randomly
distributed. The source is not polarized