Kvartbølgeplater

Kvartbølgeplater, also known as quarter-wave plates, are optical components used to manipulate the polarization state of light. They are made from birefringent materials, meaning they have different refractive indices for light polarized along different axes. This property causes light polarized along one axis, the fast axis, to travel faster than light polarized along the other axis, the slow axis.

A kvartbølgeplate is specifically designed so that the difference in optical path length between the fast and slow axes is equal to one-quarter of the wavelength of the incident light. When linearly polarized light enters a kvartbølgeplate at an angle of 45 degrees to its optical axes, the light is resolved into two components polarized along the fast and slow axes. Due to the quarter-wave retardation, these two components emerge with a phase difference of 90 degrees. This phase difference transforms the linearly polarized light into circularly polarized light. Conversely, if circularly polarized light is incident on a kvartbølgeplate, it will be converted into linearly polarized light.

By rotating the input polarization or the kvartbølgeplate itself, various polarization transformations can be achieved, including converting linearly polarized light into elliptically polarized light. Kvartbølgeplater are commonly used in optical instruments such as polarimeters, ellipsometers, and in systems requiring precise control of light polarization, like some types of lasers and optical modulators. They are typically manufactured from materials like quartz, mica, or birefringent polymers.