neljännesaaltopaneelista

A neljännesaaltopaneeli, or quarter-wave plate in English, is an optical device that modifies the polarization state of light. It consists of a birefringent material, such as a crystal or a specially prepared polymer, with a thickness equal to one-quarter of the wavelength of the light being used. Birefringence means the material has different refractive indices for light polarized along two perpendicular axes, known as the fast and slow axes.

When linearly polarized light enters a quarter-wave plate, it can be considered as a superposition of two components, each polarized parallel to the fast and slow axes. Due to the differing refractive indices, these two components travel at different speeds through the material. This speed difference causes a phase shift between them. If the light is incident at a 45-degree angle to the fast and slow axes, the phase shift after traversing the plate will be exactly 90 degrees or pi/2 radians.

This 90-degree phase shift transforms the linearly polarized light into circularly polarized light. Conversely, circularly polarized light can be converted into linearly polarized light by a quarter-wave plate. Other polarization states can also be manipulated, for example, transforming linearly polarized light into elliptically polarized light if it is not incident at 45 degrees. Quarter-wave plates are essential components in various optical instruments and technologies, including polarimeters, liquid crystal displays (LCDs), and in the manipulation of laser beams.