Moving the View Angle slider rotates the rectangular medium orientation to give different perspective views of the phenomenon. The optical properties of the insulating surface determine the exact amount of reflected light that is polarized. Mirrors are not good polarizers, although a wide spectrum of transparent materials act as very good polarizers, but only if the incident light angle is oriented within certain limits.
An important property of reflected polarized light is that the degree of polarization is dependent upon the incident angle of the light, with the increasing amounts of polarization being observed for decreasing incident angles. When considering the incidence of non-polarized light on a flat insulating surface, there is a unique angle at which the reflected light waves are all polarized into a single plane.
This angle is commonly referred to as Brewster's angle , and can be easily calculated utilizing the following equation for a beam of light traveling through air:. By examining the equation, it becomes obvious that the refractive index of an unknown specimen can be determined by the Brewster angle. This feature is particularly useful in the case of opaque materials that have high absorption coefficients for transmitted light, rendering the usual Snell's Law formula inapplicable. Determining the amount of polarization through reflection techniques also eases the search for the polarizing axis on a sheet of polarizing film that is not marked.
The principle behind Brewster's angle is illustrated in Figure 1 for a single ray of light reflecting from the flat surface of a transparent medium having a higher refractive index than air. The incident ray is drawn with only two electric vector vibration planes, but is intended to represent light having vibrations in all planes perpendicular to the direction of propagation.
For a qualitative understanding of the vanishing reflectivity, one can consider the oscillating electric polarization in the second medium, which is perpendicular to the direction of the vanishing reflected beam. It is well known that dipoles do not emit radiation exactly in the direction of their oscillation. However, that picture is not providing a real explanation; for example, it is not clear why the direction of electric polarization in the second medium should be relevant, although the reflected beam would propagate in the first medium.
Optical elements in laser resonators or other optical setups are often oriented such that a laser beam propagating through them is at Brewster's angle. That way, reflection losses are avoided for p-polarized light without requiring any anti-reflection coatings. The advantage is not only that such coatings are not required, but also that the realistically achieved effective reflectivities are typically lower with that technique.
However, various disadvantages can result from that approach — for example, astigmatism of focused beams, which may require additional components or design details in order to avoid detrimental effects. Examples for optical elements which are often used at Brewster's angle are laser crystals , birefringent tuners , prism pairs for wavelength tuning or dispersion compensation , and Brewster windows in gas lasers.
In case of prisms , this technique can of course work at the input and output face only if the angle between the two surfaces is correctly chosen. For example, for a prism made of fused silica SiO 2 and the wavelength of nm, where the refractive index is 1. In principle, one can obtain a strong and adjustable attenuation of a polarized laser beam by reflecting it e.
The problem of that technique, however, is that the reflectivity for s-polarized light is then much higher; even if the incoming beam is quite well polarized, a small s-polarized component of it could play a dominant role in the reflected beam.
As explained in the article on depolarization loss , some s-polarized components can easily be generated under certain circumstances.
Disturbing optical reflections from water surfaces can be substantially attenuated with polarizing glasses, transmitting only vertically polarized light. Although the angle of incidence of sunlight may often deviate substantially from Brewster's angle, the reflectivity for p-polarized is generally much lower than for s-polarized light.
Answer from the author :. Only for p polarization, we can have the situation that for a suitable angle of incidence the E-field direction in the medium is perpendicular to the direction into which the reflected light would go.
Under those condition, no light can go there. For s polarization, that could not happen. A Brewster angle is the angle at which an incident beam of unpolarized light gets reflected after the complete polarization is known as the Brewster angle or polarizing angle.
Because of this, the polarizing angle gets linearly polarized by having its electric field vectors parallel to the plane of the reflecting surface and perpendicular to the plane of incidence.
At other angles, the reflected lights get partially polarized. With the help of the Brewster law, the magnitude of Brewster's angle deviation depends upon the refractive indices of the involved optical channel and can be calculated. So, what is the Brewster angle? Where n1 is the refractive index of the medium through which light propagates and n2 is the refractive index of the medium through which light reflects. The above equation is useful for determining the refractive index of an unknown specimen such as opaque material with a high absorption coefficient for light transmission.
From the above arrangement, to obtain the disappearing reflection losses at the Brewster plate, the angle of incidence and Brewster's angle must be coincident, and light must be polarized, i. The light reflected from the surface at Brewster's angle produces shining effects. In modern lasers , Brewster's angle is an important concept to create linearly polarized light by reflections at the mirror surface of the laser cavity.
0コメント