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This equation, Bragg's law, describes the condition on θ for constructive interference. [12] A map of the intensities of the scattered waves as a function of their angle is called a diffraction pattern. Strong intensities known as Bragg peaks are obtained in the diffraction pattern when the scattering angles satisfy Bragg condition.
When the incident light beam is at Bragg angle, a diffraction pattern emerges where an order of diffracted beam occurs at each angle θ that satisfies: [3] = Here, m = ..., −2, −1, 0, +1, +2, ... is the order of diffraction, λ is the wavelength of light in vacuum, and Λ is the wavelength of the sound. [4]
Diffraction from a large three-dimensional periodic structure such as many thousands of atoms in a crystal is called Bragg diffraction. It is similar to what occurs when waves are scattered from a diffraction grating. Bragg diffraction is a consequence of interference between waves reflecting from many different crystal planes.
Sound waves produce a refractive index grating in the material, and it is this grating that is "seen" by the light wave. [1] These variations in the refractive index, due to the pressure fluctuations, may be detected optically by refraction, diffraction, and interference effects; [ 2 ] reflection may also be used.
The dynamical theory of diffraction considers the wave field in the periodic potential of the crystal and takes into account all multiple scattering effects. Unlike the kinematic theory of diffraction which describes the approximate position of Bragg or Laue diffraction peaks in reciprocal space , dynamical theory corrects for refraction, shape ...
This ensures that if the Laue equations are satisfied, then the incoming and outgoing (diffracted) wave have the same phase at each point of the crystal lattice, so the oscillations of atoms of the crystal, that follows the incoming wave, can at the same time generate the outgoing wave at the same phase of the incoming wave.
Portrait of William Lawrence Bragg taken when he was around 40 years old. Sir William Lawrence Bragg (31 March 1890 – 1 July 1971), known as Lawrence Bragg, was an Australian-born British physicist and X-ray crystallographer, discoverer (1912) of Bragg's law of X-ray diffraction, which is basic for the determination of crystal structure.
Diffraction from a periodic grating, regardless of electromagnetic or matter wave, can be roughly divided into two regimes: the Bragg regime and Raman-Nath regime. In the Bragg regime, essentially only one diffraction peak is produced. In the Raman-Nath regime, multiple diffraction peaks can be observed. [4]