Brewster angle determination
Aim: 1.To measure the Brewster angle and hence
to find the refractive index of the transparent material.
Apparatus: Bread Board, Laser diode, polarizer, rotator,
sheet of transparent material (microscope glass slide), photo detector, Detector output
A beam of light incident on a dielectric transparent material can be resolved into parallel (p)
and orthogonal (s) components. Brewster discovered that at a particular angle of incidence ?B
(called Brewster angle); reflection coefficient of P-component goes to zero. In this condition
the reflected and transmitted beams are orthogonal to each other.
By Snell’s law, tan ?B=n
n- refractive index of the material. Procedure:
1.Mount diode laser to the laser mount. 2.Switch on the laser and place the polarizer
rotator in front of it so as to make the E-field parallel to the bread board.
3.Mount the glass slide on the rotational stage.
4.Orient the microscope slide to reflect the laser beam back into the laser output aperture.
5.Rotate the glass slide slowly and note the intensity of the reflected beam from the glass
slide. (By a photo detector.) 6.The intensity of the light is minimum (almost
zero) at Brewster angle ?B .Knowing ?B refractive index is calculated from the formulae, n=
tan tan ?B. Applications
Polarized sunglasses use the principle of Brewster’s angle to reduce glare from the
sun. Photographers use the same principle to remove
reflections from water so that they can photograph objects beneath the surface.