twopolarizer

Two-polarizer (also called a two-polarizer system) is a pair of linear polarizers placed in series along the same optical axis. The arrangement is used to analyze the polarization state of light and to prepare a beam with a controlled polarization by varying the relative orientation of the two polarization axes.

Principle: For ideal polarizers and monochromatic light that is already linearly polarized along the first polarizer, the transmitted intensity after the second polarizer, whose transmission axis makes an angle θ with the first, follows Malus's law: I_out = I_in cos^2 θ. If the input is unpolarized, the first polarizer yields I_in/2, and the second transmits I_out = (I_in/2) cos^2 θ.

Non-idealities: Real polarizers have finite extinction ratios and wavelength dependence, so the simple cos^2 θ law is an approximation. The full behavior can be described with Jones calculus for fully polarized light or Mueller calculus for partially polarized light.

Applications: The two-polarizer setup is widely used in experiments to measure polarization, determine the degree of polarization, calibrate detectors, and in polarization optics teaching. It can also serve as a simple polarization analyzer in imaging and spectroscopy.

See also: Malus's law, polarization, polarizer, Jones calculus, Mueller calculus.