6 - Interferometers and Polarisation Flashcards
What is a Fabry-Perot Interferometer?
In optics, a Fabry–Pérot interferometer or etalon is an optical cavity made from two parallel reflecting surfaces. Optical waves can pass through the optical cavity only when they are in resonance with it. It is named after Charles Fabry and Alfred Perot, who developed the instrument in 1899.
It creates an oscillating circular wavefront on the screen. They’re called interference fringes.
Why does the Fabry-Perot Interferometer use half-silvered plates over uncoated glass plates?
Glass plates would refract and transmit the vas majority of the light rays.
Whereas half-silvered plates refract part of the ray while splitting the rest and reflecting it into another mirror.
The other side of the half-silvered plate transmits incoming rays straight through.
How do you calculate the contrast ratio, F?
F = (4 * |R^2) / (1 - |R)^2
How do you calculate the resolution R?
R = lambda / (Delta * lambda) = ((m * pi)/2) * (F)^0.5
How do you calculate order number m?
m * lambda = 2 * t * cos(theta)
OR
R = lambda / (Delta * lambda) = ((m * pi)/2) * (F)^0.5
What is Finesse, |F?
Finesse is the ratio of separation of adjacent maxima to the resolution - higher Finesse due to higher reflectivity leads to higher better resolution.
Calculated by:
|F = (pi / 2) * (F)^0.5
When is 2 * n * t * cos(theta) used?
It is used when the two ‘sources’ are caused by the thickness of a layer. I.e. bubbles.
It is when maxima occur
How do you calculate reflectance?
|R = ((reflected amplitude) / (incident amplitude))^2
= (reflected intensity) / (incident intensity)
What is a waveplate?
A waveplate or retarder is an optical device that alters the polarization state of a light wave travelling through it.
What is circularly polarised light?
Natural light is generally unpolarized, all planes of propagation being equally probable. If the light is composed of two plane waves of equal amplitude but differing in phase by 90°, then the light is said to be circularly polarized.
What is elliptically polarised light?
If two plane waves of differing amplitude are related in phase by 90°, or if the relative phase is other than 90° then the light is said to be elliptically polarized.
What is a quarter wave plate?
A quarter-wave plate consists of a carefully adjusted thickness of a birefringent material such that the light associated with the larger index of refraction is retarded by 90° in phase (a quarter wavelength) with respect to that associated with the smaller index.
The material is cut so that the optic axis is parallel to the front and back plates of the plate. Any linearly polarized light which strikes the plate will be divided into two components with different indices of refraction.
One of the useful applications of this device is to convert linearly polarized light to circularly polarized light and vice versa. This is done by adjusting the plane of the incident light so that it makes a 45° angle with the optic axis.
What is a half wave plate?
A half-wave plate on the other hand similarly consists of a carefully adjusted thickness of a birefringent material. However, half-wave plates adjust the light such that it is associated with the larger index of refraction is retarded by 180° in phase (a half wavelength) with respect to that associated with the smaller index.
The material is cut so that the optic axis is parallel to the front and back plates of the plate. Any linearly polarized light which strikes the plate will be divided into two components with different indices of refraction.
What is linearly polarised light?
A plane electromagnetic wave is said to be linearly polarized. The transverse electric field wave is accompanied by a magnetic field wave. It oscillates on one axis.
