Malus' law

Malus' law states that an ideal polarizer transmits linearly polarized light with intensity proportional to the squared cosine of the angle between their polarization axes.

Polarization: The orientation-dependent behavior of a transverse wave, especially the direction of its electric field. Malus' law describes how an analyzer changes the intensity of polarized light.
Optical intensity: The power of an electromagnetic wave carried per unit area perpendicular to its propagation. The law predicts transmitted intensity relative to the incident intensity.
Polarimetry: The measurement of the polarization properties of light, including its rotation and ellipticity. Malus' law relates analyzer readings to the orientation of linearly polarized light.
Étienne-Louis Malus: A French engineer and physicist who discovered polarization by reflection and formulated Malus' law. His experiments established the intensity relation named after him.
Linear polarization: A state of polarization in which a wave’s electric field oscillates along one fixed direction. The incident light in the law has a definite polarization axis.
Electric field: A vector field that exerts forces on electric charges and forms part of an electromagnetic wave. The analyzer transmits the component of this field aligned with its axis.
Optical rotation: The rotation of a light wave’s polarization plane as it passes through an optically active material. An analyzer can quantify the rotation by measuring intensity as its axis turns.
Polarization by reflection: The production of polarized light when unpolarized light reflects from a surface. Malus encountered polarization while studying reflected light.
Optical axis: A direction in an optical system associated with a defined orientation or symmetry of light propagation or transmission. The analyzer’s transmission axis sets the angle used in Malus' law.
Projection (linear algebra): The component of a vector retained along a specified direction or subspace. The analyzer projects the incident field onto its transmission axis.

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