May 6 2014
A dispersive prism is a type of optical prism that divides the incident light into different colors of the electromagnetic spectrum. The colors thus produced will have different velocities, as their refraction index changes with wavelength.
An Amici prism is a kind of dispersive prism commonly used in direct-vision spectrometers. Named after the astronomer Giovanni Amici, an Amici prism is also known as a right angle prism, as it produces inverted images and bends the line of vision through a 90° angle.
This prism is designed so that the transmitted light is dispersed by a dihedral edge between the roof surfaces of the prism.
Working Principle of Amici Prisms
A typical Amici prism consists of two triangular prisms, made of a medium-dispersion crown glass and high-dispersion flint glass, respectively.
Both the prisms are in contact with each other. Light rays of particular wavelength incident on the first prism are refracted at the first air-glass interface, and again at the interface between the triangular prisms. Following refraction, the light rays exit the second prism.
The materials and prism angles are selected so that the refracted light leaves the prism in a direction parallel to the incident beam. Other light rays incident on the prism are deflected, based on the glass dispersion properties of the materials. Thus, the optical spectrum of the incident light can be obtained by viewing the light source via the prism.
Double Amici Prisms
A double Amici prism is a three-prism arrangement produced by joining two Amici prisms back-to-back. It is designed such that a zero deflection angle is produced, following the occurrence of refraction of incident light at its internal surface. This refraction occurs at a wavelength-dependent beam offset.
The doubling of original Amici prisms allows the refraction of a center wavelength of light back to the line of incident beam, thereby improving the dispersion properties of light. Thus, the light exiting the prism will not deviate from the line of incident light, and it does not undergo transverse displacement.
Applications of Amici Prisms
Amici prisms are well-suited for spotting scopes, or any optical device that produce inverted images. Double Amici prisms, on the other hand, can be employed in low-resolution spectrometers.
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